SSA 2011
April 13–15
Memphis, Tennessee

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Do I smell? I smell home cooking.
It’s only the river, it’s only the river.

William B. Joyner
Memorial Lectures

The William B. Joyner Memorial Lectures were established by SSA in cooperation with the Earthquake Engineering Research Institute (EERI) to honor Bill Joyner's distinguished career at USGS and his abiding commitment to the exchange of information at the interface of earthquake science and earthquake engineering, so to keep society safer from earthquakes. Joyner Lecturers are chosen on the basis of their work at this interface, whether they are contributions from earthquake science to earthquake engineering or from earthquake engineering to earthquake science.

This year's lecturer, Thomas Hanks of USGS Menlo Park, will speak Thursday at 6:15 PM in the Heritage Rooms on Extreme Ground Motions
(see abstract below).

Abstract
Extreme Ground Motions are the extremely large amplitudes of earthquake ground motions that arise at extremely low probabilities of exceedance (hazard levels). They were born in the extension of the 1998 probabilistic seismic hazard analysis (PSHA) for Yucca Mountain (Stepp et al., 2001) to a hazard level of 1E-8/yr (1E-4 for a 10,000-year repository lifetime). This gave rise to peak ground accelerations (PGA) 11g and peak ground velocities (PGV) 13 m/sec, ground-motion values that caused considerable consternation in many sectors of earthquake-science and earthquake-engineering circles. In 2005, the U.S. Department of Energy launched a five-year research program (ExGM) to investigate the origin, nature, and plausibility of extreme ground motions. This presentation will be a very brief summary of what we have learned in the course of ExGM, in which several dozen scientists and engineers participated. The three basic themes of ExGM research are physical limits to ground motion in bedrock, unexceeded ground motions, and frequency of occurrence of various ground-motion measures (such as PGA and PGV) or things that control them (such as earthquake stress drops or faulting displacements). Physical limits define ground motions that cannot occur, ever. Unexceeded ground motions are ground motions that have not yet occurred, as presented by fragile geologic structures of known lifetime, but may occur at any time. Fragile geologic structures are the only way to validate (or invalidate) PSHA calculations over long periods of time. Frequency-of-occurrence research focused on various distribution functions, which control the aleatory uncertainty in PSHA that is especially important at low hazard levels. The specific application of the methods, models, and data we developed in the course of ExGM is to seismic hazards for Yucca Mountain; we find that the 1998 mean seismic hazard curve significantly overstates the seismic hazard we infer from the findings of ExGM research. The methods and models developed in the course of ExGM are quite general, however, and may be applied to critical facilities anywhere in the world; they will be especially valuable at the low hazard levels that ExGM confronted.
Earthquake Debates: Is Testing and Evaluating Earthquake Forecast Models a Worthwhile Effort?
Conveners: Danijel Schorlemmer, USC / SCEC, David D. Jackson, UCLA, and Warner Marzocchi, Istituto Nazionale di Geofisica e Vulcanologia (Italy), and Matthew C. Gerstenberger, GNS Science (New Zealand)
Seismic hazard assessment is an inherently difficulty problem because not all physical, geological, and statistical aspects of earthquake generation, nucleation, and occurrence are well understood. Hazard assessment employs many concepts that, even after decades or research, remain contentious. Invited speakers with strong positions will present their case on these issues:
  • Should earthquake early warning be implemented and the public be educated for its use? Is early warning ready for prime time or is its premature use creating new unsolved problems and even increasing the danger?
  • Is testing and evaluating earthquake forecast models a worthwhile effort? Will the information gain of such efforts be large enough in the next years to decades that new constraints could be put on seismic hazard assessment? Is forecast testing a good way to evaluate hypotheses of earthquake behavior, or does it force earthquake information into unnatural formats?
Earthquake Debates: Should Earthquake Early Warning be Implemented?
Conveners: Danijel Schorlemmer, USC / SCEC, David D. Jackson, UCLA, and Warner Marzocchi, Istituto Nazionale di Geofisica e Vulcanologia (Italy), and Matthew C. Gerstenberger, GNS Science (New Zealand)
Seismic hazard assessment is an inherently difficulty problem because not all physical, geological, and statistical aspects of earthquake generation, nucleation, and occurrence are well understood. Hazard assessment employs many concepts that, even after decades or research, remain contentious. Invited speakers with strong positions will present their case on these issues:
  • Should earthquake early warning be implemented and the public be educated for its use? Is early warning ready for prime time or is its premature use creating new unsolved problems and even increasing the danger?
  • Is testing and evaluating earthquake forecast models a worthwhile effort? Will the information gain of such efforts be large enough in the next years to decades that new constraints could be put on seismic hazard assessment? Is forecast testing a good way to evaluate hypotheses of earthquake behavior, or does it force earthquake information into unnatural formats?

Town Hall Meeting

“Before there was a Memphis: the New Madrid Earthquakes of 1811-1812” is the topic of a public meeting to understand the early history (1782-1810) of southwest Tennessee and large sequences of earthquakes that have occurrred several times in the Central U.S. over the past 1500 years. An overview will also be provided on upcoming New Madrid Bicentennial events in the Memphis area.

Speakers will include the incoming SSA President; Memphis Mayor A. C. Wharton; Jimmy Ogle, Memphis History Lecturer; Kent Moran, Historian at The Center for Earthquake Research in Information; Buddy Schweig, USGS; and Chuck Langston, CERI Director.

The meeting will be held 7:00-8:30 Wednesday evening, April 13, 2011 in the Cannon Center. The event will be open to the public for the purpose of informing the general population and public officials about earthquake-related issues.

Session:   Talking Hazards: A Dialogue on the Future of USGS Natural Hazards Science
USGS seeks input for planning investments in its natural hazards mission area.
This 90 minute session extends through the break. People are invited to come and participate for as much or little time as their schedule permits.
Archeoseismology: Learning about Ancient Earthquakes from the Archeological Record
Conveners: Tina M. Niemi, University of Missouri-Kansas City, Klaus -G. Hinzen, University of Cologne, and Martitia P. Tuttle, M. Tuttle & Associates
This session is organized jointly by SSA and the European Seismological Commission (ESC).
Evidence of large earthquakes before the advent of modern seismometers is derived from historical, geological, and archaeological records. In this session, we explore the field of archaeoseismology the study of the evidence of ancient earthquakes at archaeological sites. Archaeological records have the potential of yielding valuable data relevant to the timing of ancient earthquakes as well as to intensity of ground shaking and parameters of fault rupture. Many archaeological sites contain abundant material useful for precise dating and regional correlation of earthquake effects that are necessary for estimating the timing, locations, magnitudes, and recurrence of large earthquakes. Because many of them have been occupied over a long period of time, archeological sites may have experienced multiple cycles of seismic activity and contain records of long-term behavior of faults. In addition, earthquake-related ground failure may disturb the archeological record. The challenge for archaeoseismic research is to decipher the evidence of ancient earthquakes within this archaeological-geological context. This session explores the records of earthquakes at archaeological sites and methods for quantifying seismic hazard parameters from archaeoseismic data. Papers from around the globe, including Asia, Europe, the Middle East and Mediterranean, as well as the Americas will be presented. This session sponsored by International Geoscience Programme IGCP 567 "Earthquake Archaeology."
Assessment of Seismic Hazard from Paleoliquefaction Studies
Conveners: Russell A. Green, Virginia Tech and Scott M. Olson, University of Illinois at Urbana-Champaign
The use of paleoseismic studies for the seismic hazard in regions of low-to-moderate seismicity has increasingly become formalized. The focus of this session will be on the new developments and/or applications of paleoseismic studies for assessing the seismic hazard. Particular emphasis of this session is the interdisciplinary collaborations among geologists, geotechnical engineers, and seismologists on paleoliquefaction studies.
Broadband Ground-Motion Time Series Generation
Conveners: Leonardo Ramirez-Guzman, USGS - Denver, CO, Morgan Moschetti, USGS - Golden, CO, and Yuehua Zeng, USGS - Golden, CO, and Robert Graves, USGS - Pasadena
In recent years, significant progress has been achieved in both observation and theoretical modeling of earthquake strong-ground motions. Unfortunately, the database of recorded near-fault ground motions from large to great earthquakes is still very limited, especially in regions where these types of earthquakes are most likely to occur. Recent advances in physics-based deterministic and stochastic ground motion modeling approaches have made it possible to simulate realistic broadband time series, which can be used to augment the sparse recorded data, as well as for engineering design applications. The aim of this session is to examine the status of different techniques used to generate broadband synthetic seismograms, and to document their limitations and usefulness. This session will cover many aspects of broadband strong ground motion simulation, including kinematic and dynamic earthquake rupture characterization, deterministic ground motion simulation, and high frequency synthesis techniques. Papers will also be presented on criteria to quantify the goodness-of-fit between observed and synthetic seismic data, examples of applications to earthquake engineering problems and computational platforms that address end-to-end time series generation.
Combining Geodetic and Seismic Measurements
Conveners: David Mencin, Kathleen Hodgkinson, UNAVCO, and Charles A. Langston, University of Memphis
Combining geodetic and seismic measurements provides the potential to expand the spectrum of signals that can be observed at a site, enhance our understanding of the earthquake process and develop in-situ calibration methods for borehole instruments. The combination of tilt and seismic measurements in Japan, strainmeter recordings of Episodic Tremor and Slip strain pulses in Cascadia and the measurement of slow earthquakes in central California are examples of the types of signals borehole instruments have captured well. Combining borehole geodetic, seismic and GPS measurements would enhance our understanding of how strain transients develop. With higher sample rates, improved sensitivities and the increasing number of integrated geodetic and seismic networks around the world, the task of combining the different data sets to obtain new insight on the temporal and spatial evolution of high to ultra low frequency signals becomes a pressing challenge. In this session, we will present papers on combining GPS, seismic and borehole geodetic measurements for the purposes of data processing, down hole instrument calibration and modeling of geophysical signals. The session also covers several aspects of dealing with integrated networks including installation operation, and, tasks associated with handling the large volumes of data generated by these networks.
Creative Wavefield Recording and Analysis
Conveners: Horst Rademacher, Guralp Systems Ltd and Justin Rubinstein, US Geological Survey
This session is comprised of a series of talks and posters related to seismic instrumentation, large scale seismic networks, methods for calibrating seismic arrays, and geodetic methods for analyzing seismic wavefields.
Earth Structure Observations and Theory
Conveners: Vladislav Martynov, Univ of CA San Diego and Rachel Murphy, Univ of Wisconsin - Madison
Earth structure observational studies, theoretical elastic and anelastic effects on wave propagation, and ground motion studies related to site classification.
Earthquake Triggering and Induced Seismicity
Conveners: Stephanie Prejean, USGS Alaska Volcano Observatory and Sean R. Ford, Lawrence Livermore National Laboratory
Observational studies are presented that give clues to how and when earthquakes are triggered by natural and unnatural stress changes due to volcanic eruption, fluid injection, or through wave propagation of large-amplitude seismic waves.
Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Conveners: Mark Leonard, Australian Geological Survey and Stephane Mazzotti, Geological Survey of Canada
Recent geological and numerical modeling studies suggest that faulting and seismicity in continental intraplate regions may follow complex episodic patterns, with spatial migration along large geological structures and sporadic periods of activity followed by long periods of quiescence. The implications of such potential behavior on seismic hazard assessment are poorly understood, but could result in significant modifications to current hazard models. This session covers various aspects of the complexity of continental intraplate faulting through geological, seismic, geodetic, crustal rheology, and numerical modeling studies. Some presentations will compare and combine multi-disciplinary data while others explore the impact of complex and episodic seismicity on seismic hazard assessment.
Geometry Effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Conveners: Dominic Assimaki, Georgia Tech, Alan Yong, USGS - Menlo Park, and Adrian Rodriguez-Marek, Virginia Tech
Increasingly, seismic hazard assessment and microzonation studies are relying on wave motion stimulations to estimate the distribution of expected ground motions. Observations from large earthquakes have shown that — among other factors — the presence of irregular geomorphic and geologic structures can significantly aggravate the catastrophic consequences of seismic motion as a result of preferential focusing, scattering and/or trapping of seismic energy. Examples of such 'geometry' driven effects include significant spatial variability of seismic intensity over small distances, increase of duration in expected shaking, and the altering of frequency content including amplification. In practice, however, typical, seismic code provisions and microzonation studies do not account for these effects despite the documented evidence of their role in elevating seismic risk. the purpose of this session is to facilitate the dissemination of recent advances in the understanding, monitoring, modeling and simulation of geometry-related effects in ground motion, and to focus attention on the implications of these effects in seismological research and engineering design. In particular, specific topics include, but are not limited to, numerical-modeling methods that account for topographic effects, basin wedge effects, near-surface waveguides or reflectors, and observations of ray focusing and defocusing and their correlation with structural damage intensity and spatial distribution, as well as procedures to account for geometry effects to be employed in seismic hazard assessment and mitigation procedures.
Geotechnical Lessons Learned from Recent Earthquakes: Haiti, Chile, Baja CA, New Zealand
Conveners: Dominic Assimaki, Georgia Tech and Susan Hough, Cal Tech / USGS - Pasadena
Papers in this session focus on observations, simulations and back-analyses of geoengineering case-studies from recent significant earthquakes, including the 12 January 2010 Mw7 Haiti Earthquake, the 27 February 2010 Mw8.8 Chile Earthquake, the 4 April 2010 Mw7.2 Sierra El Mayor Earthquake in Baja California, and the 03 September 2010 Mw7.0 South Island of New Zealand Earthquake. Multiple geotechnical engineering phenomena were documented during the post-event reconnaissance of these events, including liquefaction and lateral spreading, site effects, topographic effects, landslides, and failures of foundations and retaining structures. The focus of this session is the dissemination of case-studies involving, for example, analyses of macroseismic observations, geotechnical investigations, mainshock and aftershock recordings, and remote sensing imagery; as well as numerical simulations and simplified analytical models, that can be used by the engineering and seismological communities to evaluate the effectiveness of established predictive models and design procedures, and accordingly improve existing hazard prediction and mitigation strategies for future events.
Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Conveners: Vladimir Graizer, US Nuclear Regulatory Commission and Chris Cramer, University of Memphis
Various ground motion attenuation models, often called ground motion prediction equations (GMPE), have been developed in recent years for different tectonic environments. Because of their importance for engineering applications, dozens of papers on this area were recently published in engineering and seismology journals and conference proceedings. Approaches to ground motion attenuation modeling vary significantly between developers including differences in the approximation of the attenuation function (functional form), the selection of geophysical input parameters (fault parameters, travel path, Vs, basin depth, etc.), and the modeling of the standard error for prediction. Presentations from a wide group of earthquake engineering professionals (model developers and users) will discuss the bases of approaches to ground motion attenuation model developments including:
  • Approximation functions (functional forms),
  • Set of model input parameters characterizing fault, path and site (we encourage participants to make a list or table of input parameters used in the model),
  • Modeling standard error including regions where observational data is limited
  • Testing and verification criteria.
This discussion is timely because of a number of accomplished and ongoing studies, such as next generation attenuation projects: NGA-West, NGA-West-2, and NGA-East involving researchers and data from around the world.
Ground Motion Scaling and Selection
Conveners: Shahram Pezeshk, University of Memphis
This session will cover issues related to "Ground Motion Scaling and Selection." Design acceleration response spectrum is generally used by engineers for linear structural analysis of typical regular structures. The design spectrum for a given site is typically obtained from a uniform hazard spectrum (UHS). Whilst the starting point for seismic design may be a UHS produced by probabilistic seismic hazard analysis (PSHA), many researchers and practitioners are now arguing that the UHS itself is not an appropriate basis for design. It is preferable to disaggregate the hazard and then construct a scenario response spectrum, or even a conditional mean spectrum. Time history analysis may be required when nonlinear performance of a structure needs to be addressed. Instances that require time history analysis include very tall or long structures, complex buildings with extreme mass and/or geometric irregularities, structures with base isolation or supplementary damping devices, structures designed for high ductility demand, and particularly critical structures for which any damage has potentially far-reaching consequences in terms of safety. One way to obtain the needed time histories is to generate artificial ground motions to match the target design spectrum. Alternative approach would be to select a suite of real ground motions from analogous past seismic events recorded in similar site conditions. However, there is not much chance of finding real ground motions that their response spectra coincide with a desired response spectrum. This session will discuss recently developed procedures for ground motion scaling and selection.
Guide to Sustainable Seismographic Networks
Conveners: Stephen D. Malone, University of Washington and John R. Filson, USGS National Center
The purpose of this session is to lay the foundation for a written guide to sustained seismic network operations. Sustaining the operations of a seismic network is a complex and challenging task. This challenge can be cast into four major elements: (1) establishing a base (or bases) of support, (2) network installation, operations and maintenance, (3) routine data processing, and (4) information and data dissemination. The last element should feed back into the first, so that the supporting groups see the value in network and its products. This session explores the practical issues in building a sustainable seismic network and presents case studies of sustainable networks operations and experiences in various countries and situations. The true test of any network often comes during an earthquake or volcanic emergency. On the compressed time scale of a volcanic crisis or earthquake disaster recovery, it can be difficult to find a reliable and yet disinterested source of information. If a network fails to meet expectations in a crisis long-term support could be endangered. The challenges of network operations in various emergency and post emergency situations will be emphasized. The session also presents examples of advanced technologies and procedures that may be applied in future network operations.The oral presentations will end with a discussion period on the contents of a guide to sustainable networks during which the views, opinions, and experiences of the speakers and audience will be most welcome.
Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Conveners: Kishor Jaiswal, Emily So, USGS - Golden, CO, and Doug Bausch, FEMA, and Helen Crowley, Global Earthquake Model
An earthquake loss estimation model, developed with the vulnerability of the affected building stock at its center depends on good, reliable data for its success. Since the advent of HAZUS, there have been considerable efforts within the US and abroad to improve on ways of capturing, classifying, and analyzing building stock inventory and their vulnerabilities. In addition, researchers around the world have also explored social vulnerabilities, depicted in part by the consequences of building collapses on its occupants. Disasters in the past have clearly highlighted the need to improve on data quality for effective catastrophe risk management. The aim of this session is to collate and draw on some notable recent efforts in this research area, in particular from FEMA in its updates for HAZUS, the USGS PAGERs initiative, EERIs World Housing Encyclopedia framework and the Global Earthquake Model (GEM), among others. This session will be used to highlight new approaches to improving inventory and vulnerability of physical and social data for use in earthquake loss modeling.
Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Conveners: Michael R. Brudzinski, Miami University of Ohio and Heather DeShon, University of Memphis
Subduction zones are a primary feature of the dynamic Earth that produce the largest earthquakes in the historic record as well as earthquakes ranging from simple to complex, extending to over 600 km depth. Despite the hazard implications, the processes that control seismogenesis have remained enigmatic. The growth of observational networks and computational capabilities over the past decade provide new opportunities to investigate subduction zone earthquakes and transitions in lithospheric and seismogenic behavior in greater detail. This session includes presentations that integrate observations of slip processes with geodynamic modeling and spatial variations in earth structure of subduction zones and other margins. A range of source process studies on recent great earthquakes, intermediate and deep earthquakes, and the new family of slow earthquakes and tremor will provide valuable contributions.
Joyner Lecture
Conveners: SSA, SSA
The William B. Joyner Memorial Lectures were established by the Seismological Society of America (SSA) in cooperation with the Earthquake Engineering Research Institute (EERI) to honor Bill Joyner's distinguished career at the U.S. Geological Survey and his abiding commitment to the exchange of information at the interface of earthquake science and earthquake engineering, so to keep society safer from earthquakes. Joyner Lecturers are chosen on the basis of their work at this interface, whether they are contributions from earthquake science to earthquake engineering or from earthquake engineering to earthquake science. More info on the Joyner Lectures is available here.
Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Conveners: M. Beatrice Magnani, University of Memphis and Martitia P. Tuttle, M. Tuttle & Associates
Occurrences of large earthquakes in continental plate interiors is poorly understood and not accounted for in the current plate tectonic theory. Understanding the long-term behavior of faults is key to constraining models of seismogenesis and assessing earthquake hazards in intraplate regions. This session focuses on recent advances in deciphering and modeling the geological and geophysical records of fault behavior in intraplate settings and their implications for seismogenesis and earthquake hazard assessment. Papers will be presented in the fields of geomorphology, neotectonics, paleoseismology, geodesy, and high resolution imaging for regions including Australia, Europe, China, India, Mongolia, Canada, and the United States.
Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Conveners: Chris Cramer, University of Memphis and Robert Williams, USGS - Denver, CO
Microzonation and urban seismic hazard mapping efforts have been in the forefront of interfacing geoscience and engineering with public and private policy and decision making. In the U.S. urban hazard mapping projects have been ongoing for a decade in Memphis, TN, Seattle, WA, Oakland, CA, St. Louis, MO-IL, Evansville, IN, and most recently in the Salt Lake City, UT region and Reno, NV metropolitan area. In Canada, Europe, and around the world, as well as the U.S., microzonation projects have been conducted for decades. Many approaches and varying levels of detail have been employed in microzonation and urban hazard mapping. Different efforts worldwide can benefit from reviewing what has been successful, in terms of scientific approach, response by the local community to the hazard assessments, post assessment community land use changes, and discussing what are the future needs and directions in this field. Criteria for prioritizing future areas for detailed earthquake shaking and liquefaction hazard studies are also needed to help funding agencies make cost-effective decisions. This session will cover many aspects of microzonation and urban hazard mapping with an emphasis on current efforts and future directions.
Multivariate Approaches to Earths Seismic Structure
Conveners: Monica Maceira, Los Alamos National Laboratory, Haijing Zhang, MIT, and Charlotte Rowe, Los Alamos National Laboratory
A recent trend in the Earth's structure modeling arena at various scales is the multivariate inversion of traditionally distinct data sets for improved seismic structure modeling. Combinations of data sets used in these multivariate inversions have included: resistivity and magnetotelluric data; receiver functions and surface wave dispersion observations; teleseismic or local travel times and gravity data; and surface wave velocity and gravity observations among others. Although multiple geophysical observations have been successfully inverted jointly, many questions about means and methods still remain unanswered. This session includes presentations on simultaneous and sequential multivariate inversion methods for improved seismic structure modeling. Some will highlight novel combinations of data sets, relationships between the independent observations and the relative weighting of disparate data sets for successful inversion. Also included are results from reservoir scale to global scale and new means to address computational efficiency and robustness of the inversion.
New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Conveners: Eugene Schweig and Robert Williams, USGS - Denver, CO
December 16, 2011, will mark the 200th anniversary of the beginning of the New Madrid earthquake sequence, a stunning cluster of three or four M7-8 earthquakes that occurred over a 54 day time span in the sparsely populated Louisiana Territory, about 240 km south of St. Louis. Ground shaking from these mainshocks was felt over the entire eastern United States and awakened people in the middle of the night up to 1400 km from the epicenters. The aftershock sequence was also impressive, with estimates of several M5-M6 earthquakes and hundreds of M3-M4s lasting for months after the mainshocks. Research over the past three decades has shown that this sequence is not an isolated event and that the New Madrid region has produced sequences of major earthquakes in 1450 A.D. and 900 A.D. These prehistoric earthquakes caused severe and widespread ground failures much like those caused by the 1811-1812 earthquake sequence. Studies have also shown that large Holocene earthquakes have occurred within the Mississippi embayment, but outside the current main microseismicity trends. To many researchers in the region, the New Madrid seismic zone poses a tremendous seismic hazard to the entire central U.S.;a repeat of this sequence would expose some 1 million people to Mercalli Intensity VII effects. Some researchers, however, have argued for lower seismic hazard and lower likelihood of repeats of an 1811-1812-type sequence. In a series of invited summary talks, this session showcases our state of knowledge of the New Madrid seismic zone, with a focus on studies of the fault zone including the extensive sand-blow area, crustal structure, personal accounts of the ground shaking, the enigmatic causes of earthquakes in this intraplate setting, and evidence for other faults surrounding the main seismicity trends that appear to have been active during the Quaternary. Contributed papers describe recent research bearing on assessments of the hazard and the risk posed by the fault zone.
Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Conveners: David Rhoades, GNS Science (New Zealand) and Delphine Fitzenz, University of Evora (Portugal)
The work of building integrative (data and physical processes), reproducible, and internally consistent seismic hazard assessment methods seems harrowing. We have gathered people who have already developed parts of the puzzle. Many probabilistic approaches are covered. In particular, the Bayesian methods seem well indicated for the task because data can be explained using generative models (physics-based or not), and, given proper priors, models' plausibility may be compared, leading to model selection or combination. The expert judgment can therefore move "upstream" from the model combination step up to the choice of the priors for example, leading to a much-needed reproducibility of the resulting hazard products. This session will deal with a probabilistic treatment of ingredients of hazard computations. E.g., GPS deformation models, past fault slip rates, fault geometry, seismotectonic zoning, rupture models of past earthquakes, fault and crust rheological models, earthquake simulators, scaling relationships (slip vs length, etc), frequency-magnitude scaling, choice of renewal models using real or synthetic data, computation and choice of ground motion prediction equations …. Contributions on 1)why it is hard to go probabilistic for certain types of work (and why it would be valuable to do so nonetheless), and 2) how to test the derived predictive models, are also included, as they will help identify areas which need more work.
Public Outreach and Seismological Data Centers
Conveners: Maurice Lamontagne, Natural Resources Canada and Chad Trabant, IRIS
This session asks how should seismologists communicate with the public in addition to reviewing interdisciplinary efforts in forecasting earthquakes and adoption of building codes. Two presentations are given on accessing seismological data products for engineering and scientific use.
Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Conveners: Adrien Oth, European Center for Geodynamics and Seismology and Kevin Mayeda, Weston Geophysical Corporation
Over the past two decades, the scaling of the earthquake rupture process and in particular whether radiated energy behaves self-similarily among small and large earthquakes, characteristics that are fundamental for enhancing our understanding of rupture physics, have been a matter of partially vigourous debate. Since the ground-breaking work of Keiiti Aki in the late 1960ties, the static scaling relation between seismic moment and some length scale characterizing the earthquake source (for which corner frequency is commonly used as a proxy) has been widely accepted, at least for earthquakes with magnitudes larger than about 3. On the other hand, the dynamic scaling of apparent stress with moment is still highly controversial throughout the entire magnitude range, from very small (M<0) to very large events (M 8 and above), and potential sources of bias such as bandwidth limitations or attenuation correction have been invoked that significantly complicate the situation. Moreover, the comparison between different studies is hampered by the fact that often different methods of analysis and/or wavefield components (i.e. direct or coda waves) are used and that many datasets employed so far covered only relatively narrow magnitude ranges. However at the same time, the sheer existence of both slow and super-shear earthquakes, for which compelling evidence has been provided, shows that the rupture dynamics, at least for large events, must span a considerable range. The aim of the session is to provide an up-to-date overview of the recent advances on the topic and to identify the challenges and routes to follow for that the seismological community may come closer to solving this issue in the years to come.This session covers earthquake scaling characteristics on all scales, from small mining-induced up to giant subduction zone events, and in particular the relationship between static and dynamic scaling laws and their implications for the earthquake rupture process. We furthermore encourage contributions dealing with the effects of potential sources of bias, comparative studies applying different methods to estimate the relevant earthquake source parameters and their impact on the scaling relationships, as well as studies dealing with the energy budget of earthquakes or events that may represent cases of end-member models of rupture dynamics, such as slow or super-shear earthquakes.
Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Conveners: Chris Cramer, University of Memphis, Richard Lee, Los Alamos National Laboratory, and Mark Petersen, USGS
Seismic hazard evaluations are important to local, regional, and national level policy and decision-making, regulation, and permitting for facility design and construction. Recent renewed interest in nuclear power generation has spurred updates to regional hazard models, particularly in the eastern North America (ENA) with the EPRI/NRC/DOE seismic source characterization and NGA East projects. The USGS national seismic hazard mapping program is planning to update the national model in 2012-13. This special session will focus on papers on recent and in progress updates to regional hazard models worldwide plus policy implications and communicating seismic hazard to the general public. The session will present aspects of recent updates in the seismic source characterization and improvements in methodology. Regional seismic hazard evaluation projects can benefit from sharing seismic hazard evaluation experiences from around the world.
Seismic Imaging: Recent Advancement and Future Directions
Conveners: Youshun Sun, MIT, Michael Begnaud, Los Alamos National Laboratory, and Po Chen, University of Wyoming
Seismic imaging is a powerful tool for geophysicists to probe the Earth's interior. The demand for higher resolution and broader range of applications is rapidly increasing. This session includes presentations on seismic imaging in various scales and application arenas, with special emphasis on recent advances and future directions. Examples include innovations and advances in 3D traveltime tomography, waveform tomography, receiver function mapping, surface wave inversion, and joint inversion of multiple geophysical observations. There will be case study papers using seismic imaging to solve real problems. Discussions on the pitfalls, limitations, and artifacts of common seismic imaging methods and potential remedies are also part of this session.
Seismic Siting for Nuclear Power Plants
Conveners: Yong Li and Laurel Bauer, US Nuclear Regulatory Commission
Due to the increasing global demand for energy, more countries are planning to expand their existing nuclear power plant fleet or include nuclear power as an optional energy source. Seismic siting for nuclear power plants is of great interest to the seismic community because of perceptions related to the potential radionuclide release resulting from strong earthquakes and associated hazards. Adequately characterizing seismic hazard for nuclear power plants is extremely important to ensuring public safety. This session focuses on seismic siting studies for nuclear power plants, including seismic source characterization, seismic wave propagation, and site amplification, and provides an interactive forum for geoscientists from various disciplines to discuss seismic siting issues for nuclear power plants. Topics that will be covered include:
  • Estimation of ground motion and its aleatory variability in stable continental regions.
  • Characterization of seismic sources: estimation of maximum magnitude and recurrence and the treatment of uncertainty.
  • Calculation of site response and its uncertainty.
  • Engineering characterization of ground motion parameters, such as Cumulative Absolute Velocity.
  • Seismic siting studies related to existing nuclear power plants and other critical facilities.
Seismic Sources and Parameters
Conveners: Debi Kilb, Scripps Inst. of Oceanography and Allison Bent, Geological Survey of Canada
A general session of oral and poster presentations pertaining to earthquake source inversion models, earthquake and exotic source seismicity, magnitudes, source mechanisms with theoretical highlights.
Seismotectonics and Hazards of Active Margins in the Circum-Caribbean Sea and Eastern Pacific Ocean
Conveners: Matt Hornbach and Sean Gulick, University of Texas Institute for Geophysics
In the wake of the 2010 Haiti and Chilean earthquakes, significant strides have been made towards understanding the tectonics and associated hazards along strike-slip and convergent margins. Yet fundamental questions remain. The goal of this session is to bring together geological/geophysical results from a diverse set of studies with the hope of developing a more comprehensive understanding of the geology as well as the processes that drive deformation and geohazards across these regions. A broad set of sub-disciplines have contributed to this session (including those working in these regions on neotectonics, geodesy, heat-flow, geomorphology, marine/land-based geology, seismology, paleoseismology and geohazards).
Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Conveners: Oliver Boyd, USGS - Memphis, Eric Calais, Purdue University, and John Langbein, USGS - Menlo Park
Large, potentially devastating, earthquakes occur within the interiors of tectonic plates where geodetically measured surface strain rates are very low (e.g. the 1811-1812 M7-8 New Madrid and 2008 M7.9 Sichuan, China earthquakes). In some cases, the paleoseismic history may suggest a relatively high rate of strain accumulation, which, if at odds with geodetic studies, can obfuscate estimates of seismic hazard. For example, geodetic measurements in the central U.S. may indicate very little overall surface deformation, an observation that may be incompatible with the relatively high frequency of large earthquakes in the New Madrid seismic zone. In this session, a series of presentations will explore surface deformation in analogous intraplate regions, whether or not observations in the New Madrid seismic zone are compatible, how variable strain rates can be over the earthquake cycle, and if a steady build up of strain responsible for repeated large earthquakes can be localized and partially masked from surface observations.
Talking Hazards: A Dialogue on the Future of USGS Natural Hazards Science
Conveners: Lucy Jones and Bob Holmes, US Geological Survey
The U.S. Geological Survey (USGS) seeks input from colleagues in academia and government at the start of the planning process for the next decade of investments in its natural hazards mission area. The USGS recently announced that it is realigning its senior leadership structure with the themes in its science strategy, one of which is hazards. As part of the realignment, teams of scientists are developing implementation plans for each strategic theme, and this listening session will inform the hazards team.
The March 2011 Tohoku, Japan and February 2011 Christchurch, New Zealand Earthquakes
Conveners: Thorne Lay, UCSC, Victor Tsai, USGS, and Gavin Hayes, USGS, and Justin Rubinstein, USGS
The Great Tohoku-Oki Earthquake of March 11, 2011 (Mw 9.0) was the largest earthquake ever recorded in Japan and one of the largest earthquakes to occur in the last century. The potential implications of this event for our understanding of great earthquakes, tsunamis, ground shaking and the many different responses to the ensuing destruction are unprecedented, partly due to the abundance of high quality data available. The Christchurch (Lyttelton) Earthquake of February 21, 2011 (Mw 6.3) also provided a wealth of information, especially regarding the impact of high intensity ground motion in an urban environment. We invite contributions that address scientific aspects of either of these two earthquakes. Potential topics include but are not limited to earthquake source modeling, tsunami observations, geodetic constraints, strong motion, tectonic setting, building response, implications for seismic hazards, and global earthquake triggering.
The Seismo-Acoustic Wavefield
Conveners: Stephen Arrowsmith, Rod Whitaker, Los Alamos National Laboratory, and Brian Stump, Southern Methodist University
Acoustic sensors are being added to all the Transportable Array seismic sites in USArray. This new dataset presents a game-changing opportunity to study the seismo-acoustic wavefield in unprecedented detail. Coupled with this development, new local and regional scale seismo-acoustic deployments have recently been deployed to study the seismo-acoustic wavefield from different sources including volcanoes, explosions, and earthquakes. Based on these recent developments, this special session will focus on all aspects of seismo-acoustics including source physics, propagation studies, and unique data sets and analyses techniques.
Verification Science
Conveners: Eric Matzel, Lawrence Livermore National Laboratory and Ross Heyburn, AWE Blacknest
Cutting edge techniques in event location and source discrimination related to nuclear verification.
Session:Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Presenter   Apostol, Andrei
Schedule   Thu 2:15 PM / Oral
Room   Ballroom C
Crustal Faults and Their Relationship To the Intermediate-Depth Seismic Activity in Vrancea, Romania
IONESCU, C., National Institute for Earth Physics, Bucharest, Romania, viorel@infp.ro; MOLDOVAN, I. A., National Institute for Earth Physics, Bucharest, Romania, iren@infp.ro; MOLDOVAN, A., AZEL Designing Group Ltd, Bucharest, Romania, iren@infp.ro; APOSTOL, A., Center for Bioseismology, Elmhurst, NY, apostoland@yahoo.com
The Vrancea seismically active region of Romania, situated far-from active plate boundaries, is characterized by small-large intermediate-depth earthquakes and small-moderate normal ones. The intermediate-depth earthquakes can be destructive when larger than magnitude 7.A bio-location method was used trying to map crustal faults and to indicate stress variations before and after intermediate-depth earthquakes. The bio-location indications can be explained by the magnetotelluric birefringence and resistivity anisotropy variations around crustal faults.Bio-location data obtained across two perpendicular crustal faults at Plostina, Vrancea, Romania, indicate a possible stress transfer from faults situated at intermediate-depth to faults situated in the Earth's crust, before and after intermediate-depth earthquakes larger than magnitude 3.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Beavers, James
Schedule   Fri 1:30 PM / Oral
Room   Ballroom D
History of Seismic Hazard EVALUATIONS at the Department of Energy Enrichment Plant, Paducah, Kentucky
BEAVERS, J. E., James E Beavers Consultants, Knoxvville, TN, jbeavers@jebconsultants.com
Seismic hazard at the Department of Energy Uranium Enrichment Plant, i.e., Paducah Gaseous Diffusion Plant (PGDP) has been a concern since the PGDP was first built in the early 1950s in support of the Cold War. Although, in those days, seismic hazard issues were raised during the construction of the PGDP as evident by historical letters and memorandum, there is no evidence that the PGDP was originally built to any seismic design criteria. It was not until the early 1970s, following the adoption of the 1969 United States Coast and Geodetic Survey sismic hazard map into the 1970 edition of the Uniform Building Code, that seismic hazard became a concern at the PGDP.This paper discusses that PGDP seismic hazard history starting with the seismic hazard issues addressed in the 1950s, the studies conducted from the 1970s through the 1990s, those conducted in the early part of the 21st Century, and those being conducted at the end of the first decade of the 21st Century. Now, based on the 1996 thru 2009 USGS seismic hazard evaluations and the recent independent studies the profession should has the hazard better defined.
Session:Ground Motion Scaling and Selection
Presenter   Jayaram, Nirmal
Schedule   Fri 11:15 AM / Oral
Room   Room 204/205
A Computationally Efficient Ground Motion Selection Algorithm for Matching a Target Response Spectrum Mean and Variance
JAYARAM, N., Risk Management Solutions, Inc., Newark, CA, nirmal.jayaram@rms.com; LIN, T., Stanford University, Stanford, CA, tinglin@stanford.edu; BAKER, J. W., Stanford University, Stanford, CA, bakerjw@stanford.edu
Dynamic structural analysis often requires the selection of input ground motions with a target mean response spectrum. The variance of the target response spectrum is usually ignored or accounted for in an ad hoc manner, which can bias the structural response estimates. This study proposes a computationally efficient and theoretically consistent algorithm to select ground motions that match the target response spectrum mean and variance. The selection algorithm probabilistically generates multiple response spectra from a target distribution, and then selects recorded ground motions whose response spectra individually match the simulated response spectra. A greedy optimization technique further improves the match between the target and the sample means and variances. It is shown empirically that this selection algorithm selects ground motions whose response spectra have the target mean and variance. The proposed algorithm is used to select ground motions for the analysis of sample structures in order to assess the impact of considering ground-motion variance on the structural response estimates. It is seen that considering the response spectrum variance does not significantly affect the resulting median response, but slightly increases the mean response and considerably increases the dispersion of the response. The implications for performance-based earthquake engineering are discussed.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Tibi, Rigobert
Schedule   Fri AM / Poster
Room   Ballroom B
An Alternative and Efficient Cluster-Link Approach for Declustering of Earthquake Catalogs
TIBI, R., Paul C. Rizzo Associates, Inc., Pittsburgh, PA, Rigobert.Tibi@rizzoassoc.com; BLANCO, J. B., Paul C. Rizzo Associates, Inc., Pittsburgh, PA, Jose.Blanco@rizzoassoc.com; FATEHI, A., Paul C. Rizzo Associates, Inc., Pittsburgh, PA, Ali.Fatehi@rizzoassoc.com
Poisson model is widely used to describe the temporal occurrence of earthquakes in probabilistic seismic hazard analysis (PSHA) studies for various reasons. The most important of these being that Poisson model is simple, yet adequate enough to describe a complex phenomenon. Studies of earthquake distribution show that sequences of earthquakes are Poissonian only after foreshocks and aftershocks have been removed from the listing. Hence, the identification and removal of foreshocks and aftershocks from earthquake catalog, a process referred to as declustering, are a prerequisite for any PSHA study based on a Poissonian model for earthquake occurrence. Two main approaches and their variants are widely used in the seismic hazard assessment community for catalog declustering: (1) the standard space-time windowing technique, such as Gardner and Knopoff (1974) method, and (2) the cluster-link scheme, such as Reasenberg (1985) algorithm or Davis and Frohlich (1991) method. Each of these methods possesses some advantages as well as shortcomings. We propose a cluster-link declustering approach that is adapted from Reasenberg’s (1985) technique, in which the interaction time window based on Poisson’s probability is replaced by a simple, but more efficient magnitude-dependent time criterion. Application of the proposed scheme to earthquake catalogs of Slovenia and the Middle East suggests that, depending on the character of the original catalog in terms of event sizes, the proposed approach identifies up to13% more dependent events, more efficiently depletes or removes clusters of earthquakes, and, as consequence, dramatically improves the fit to the expected Poisson model, with respect to Reasenberg’s (1985) method.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Babaie Mahani, Alireza
Schedule   Thu AM / Poster
Room   Ballroom B
Regional Variations In Ground-Motion Amplitudes Across North America
BABAIE MAHANI, A., University of Western Ontario, London, ON, Canada, ababaiem@uwo.ca; ATKINSON, G. M., University of Western Ontario, London, ON, Canada, gatkins6@uwo.ca
Ground motion response spectra data for moderate magnitude events have been studied to characterize differences in source and attenuation properties for different regions across North America. Understanding such differences is important for the development of ground-motion prediction equations and models, and for seismic hazard analyses. Seismograms were downloaded from regional networks in Eastern Canada, Western Canada, the central U.S. and the Pacific Northwest. Site condition estimation for each station in the database is based on available Vs30 at different stations, geological information, and estimates based on the Wald and Allen (2007) method, which uses topographic slope as a proxy to calculate Vs30. Processing of the waveforms and extraction of the ground motion amplitudes in terms of Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV) and Pseudo Spectral Acceleration (5% damped PSA) for frequencies from 0.2 to 20 Hz was performed using software from the engineering seismology toolbox (www.seismotoolbox.ca) for the waveforms from Canadian stations and the Seismic Analysis Code (SAC) for waveforms from the U.S. stations. The geometric means of ground motion amplitudes in different magnitude-distance bins for PGA, PGV and PSA at frequencies 0.2, 1, 3 and 10 Hz were compared across regions. Ground motion amplitudes from the East (New Madrid and Eastern Canada) are larger than ground motion amplitudes from events in Western Canada and the Pacific Northwest for distances larger than 100 km for all frequencies. Ground motion amplitudes from the Pacific Northwest and Western Canada are consistent for similar site conditions. The next stage of this study will compare these ground-motion amplitudes to those from network data in California.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Foster, Kevin
Schedule   Wed PM / Poster
Room   Ballroom B
Specific Barrier Model Calibration to the NGA (Next Generation of ground-motion Attenuation relations) Dataset
FOSTER, K. M., Virginia Polytechnic Institute & State University, Blacksburg, VA, kmfoster@vt.edu; HALLDÓRSSON, B., Earthquake Engineering Research Centre, University of Iceland, Selfoss, Iceland, skykkur@hi.is; GREEN, R. A., Virginia Polytechnic Institute & State University, Blacksburg, VA, rugreen@vt.edu; CHAPMAN, M. C., Virginia Polytechnic Institute & State University, Blacksburg, VA, mcc@vt.edu
The specific barrier model (SBM), proposed by Papageorgiou & Aki (1983), was used as the source term in a stochastic seismological model by Halldórsson (2004) to calibrate the model to datasets drawn from three tectonic regimes. This research applies the same calibration method to the new NGA dataset (Power et al., 2008). The performance of the seismological model of Halldórsson (2004) in generating ground motion prediction data for the recordings in the NGA dataset is evaluated. The resulting residuals are compared to those from the original calibration.A high-frequency diminution filter parameter ( ) of 0.06 resulted in the best fit of the model to the data (Halldórsson used =0.05). ∆ L=160 bars was consistent with the previous research. The seismological model performed well with the same parameters as Halldórsson's in describing a subset of NGA data associated with extensional tectonic regimes (Spudich et al., 1997).A method related by Norman Abrahamson to John Douglas (personal communication) was applied to gain insight into possible tradeoffs between and the SBM's local stress drop (∆ L) parameter. The method produces normalized response spectral plots which are sensitive to changes in but insensitive to changes in ∆ L. The results provided verification of a value of 0.06, while also highlighting that there is little tradeoff between and ∆ L in residual behavior over the frequency range examined (0.5 to 10 Hz).The seismological model underpredicts interplate data significantly at long distances (>~100 km). Several published path models for the western US were reevaluated in an effort to eliminate this discrepancy, but the path model used by Halldórsson (2004), a modification of Chin & Aki's (1991) model, was still the best-performing path term. I conclude that no published path model evaluated in this study is adequate for describing attenuation in the NGA dataset beyond 100 km.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Bezerra, Francisco
Schedule   Thu 9:00 AM / Oral
Room   Ballroom C
Influence of the Upper-Crustal Fabric on Intraplate Seismicity - The Samambaia Fault in Northeastern Brazil
BEZERRA, F. H., University of Rio Grande do Norte, Natal, RN, Brazil, bezerrafh@geologia.ufrn.br; LEGRAND, J. M., University of Rio Grande do Norte, Natal, RN, Brazil, legrand@geologia.ufrn.br; NOGUEIRA, F. C., University of Campina Grande, Campina Grande/PB/Brazil, frcezar@dem.ufcg.edu.br; FERREIRA, J. M., University of Rio Grande do Norte, Natal/RN/Brazil, joaquim@geofisica.ufrn.br; DO NASCIMENTO, A. F., University of Rio Grande do Norte, Natal/RN/Brazil, aderson@geofisica.ufrn.br
In the South American intraplate, the geometry of seismogenic faults has rarely been described due to the lack of either surface rupture or poor epicentral/hypocentral data. Here, we investigated the seismicity of the Samambaia fault, the best documented area of earthquake activity in the intraplate of South America. The period of seismicity examined occurred from 1986 to 1994 in the eastern part of the Potiguar Basin, northeastern Brazil, when more than 50,000 events were recorded. We analyzed the 3-D distribution of hypocenters and correlated them with the preexisting tectonic fabric. Our data indicate that the Samambaia fault is at least 27 km long and mainly consists of three, left-bend, en echelon segments that are spaced at 1.0 and 1.5 km apart. The segments strike at 031o – 035o, dip 70o toward NW, and exhibit focal depths between 1 and 9 km. The segments also branch off at both ends of the fault, which suggest splay terminations. The focal mechanisms indicate a dominantly strike-slip dextral movement, which induced the formation of compressional jogs where the segments seem to coalesce. This seismogenic fault reactivates the Precambrian fabric, extends upward and outcrops as a swarm of silica-rich veins and faults composed of hydraulic breccias. These veins and faults cut across Neogene and Quaternary sedimentary deposits. The fault is misoriented for reactivation under the present-day EW-trending regional compression. Field data, however, suggest that the fault may represent a channel rooted in the upper crust, where fluid ascent and where high-fluid pressure contributed to fault-weakening. We conclude that the present-day seismicity is an expression of the long-term Samambaia fault, which persisted through continuous seismic cycles.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Walsh, Lisa
Schedule   Thu PM / Poster
Room   Ballroom B
Seismicity and active fault zones in the national capital region
WALSH, L. S., The University of Maryland, College Park, MD, lsschlei@umd.edu; MONTESI, L. G. J., The University of Maryland, College Park, MD, montesi@umd.edu; MARTIN, A. J., The University of Maryland, College Park, MD, martinaj@umd.edu
On July 16th, 2010, a Mw 3.4 earthquake struck near Germantown, MD, rocking our nation’s capital. Although earthquakes in the DC metropolitan region are rare, they occur on occasion. At least 90 earthquakes have been recorded in the Mid-Atlantic region over the last 20 years. In 1828, President John Quincy Adams recorded in his diary an earthquake he experienced at the White House. Yet DC is located in a gap in the seismic hazard map developed by the USGS. The Germantown earthquake motivates us to revisit the seismic potential of faults in the vicinity of Washington DC. Ancient fault zones from Paleozoic contraction and Mesozoic extension as well as Cenozoic fault systems pervade the Piedmont metasedimentary rocks of Washington, DC, and the surrounding area. Notably the DC Fault Zone, a series of en echelon thrust faults extending from the National Zoological Park to the East Wing of the White House, shows post-Miocene offset. The larger faults in the DC Fault Zone are oriented N17°W, 60°SW and some smaller faults strike N28°E. The Germantown earthquake occurred 40 km northwest of the mapped trace of the DC Fault Zone and may have ruptured on an extension of this fault system, a new unmapped fault zone, or reactivated preexisting Paleozoic and Mesozoic fault systems. Faults in the vicinity of the earthquake epicenter generally strike N25°E to N40°E. We evaluate to what extent slip during the Germantown earthquake (oblique reverse focal mechanism, with fault plane solutions of N15°E, 57°NW or N35°W, 45°NE) may have increased stress on nearby faults by calculating regional Coulomb stress change. The stress change is small due to the minor amount of slip caused by the earthquake. However, the Coulomb stress maps indicate that the transfer of stress initiated by the Germantown earthquake may have increased the risk of future seismicity in the heart of our nation’s capital.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Van Arsdale, Roy
Schedule   Thu 11:15 AM / Oral
Room   Ballroom C
Living on the Edge - Memphis
VAN ARSDALE, R. B., University of Memphis, Memphis, TN, rvanrsdl@memphis.edu; STEVENS, K., Fugro Atlantic, Norfolk, VA, kstevens2@fugro.com; COX, R. T., University of Memphis, Memphis, TN, randycox@memphis.edu; DEEN, T., Encana Oil & Gas Inc., Dallas, TX, Tom.Deen@encana.com; VELASCO, M. S., TTI Exploration, Pleasanton, CA, solvelasco@yahoo.com; WOOLERY, E., University of Kentucky, Lexington, KY, woolery@uky.edu; HARRIS, J., Millsaps College, Jackson, MS, harrijb@millsaps.edu
Memphis is located immediately east of the southeastern bounding faults of the Reelfoot rift. Thus, major normal faults pass within 10 km of Memphis. Tertiary inversion of the old normal faults is common in this region. Ninety km north of Memphis one of these Cambrian rift margin faults has 3 km of Paleozoic normal displacement, 25-30 m of Tertiary reverse displacement, and 8-15 m of late Quaternary right-lateral transpressional slip revealed in a trench. Quaternary faulting along the eastern Reelfoot rift margin has also been documented 10 km northwest of Memphis at a second trench location in Shelby forest. Subsurface studies have been conducted east of the rift margin in Memphis and Shelby County. East-west seismic reflection lines in eastern Memphis (central Shelby County) reveal a down-to-the-east normal fault in the deep Tertiary section, but reverse faulting in the shallow Tertiary section. An anticline exposed in the bank of the Wolf River has an axial trend that strikes into the anticline identified in the reflection profile. Dating of the river bank sediments reveals that the folding occurred between A.D. 390 and 450. Bore-hole logs within Shelby County were used to make subsurface structure contour maps. These maps are interpreted to reveal five faults that displace the top of the Eocene Memphis Sand and two of these faults displace the top of the Pliocene Upland Complex. Memphis lives on the edge of the Reelfoot rift. This rift margin has documented Quaternary faulting. Faults have also been mapped east of the Reelfoot rift under Memphis and Shelby County, but only in the Tertiary section. Whether these latter faults reach the ground surface or extend into the Precambrian and pose an earthquake threat remains to be determined. It is our opinion, however, that the faults that underlie Memphis and Shelby County are outboard faults of the Reelfoot rift that merit additional study.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Kijko, Andrzej
Schedule   Fri 1:30 PM / Oral
Room   Ballroom E
Flaw in the EPRI Procedure for the Maximum Earthquake Magnitude Estimation and its Correction
KIJKO, A., University of Pretoria, South Africa, andrzej.kijko@up.ac.za
It has been proved that the EPRI, Bayesian procedure for the estimation of the regional, maximum possible earthquake magnitude Mmax, (Cornell, 1994; EPRI NP-4726), provides a value for Mmax that is biased and systematically underestimated. The value of underestimation can be as big as 0.5 unit of magnitude. The bias is caused by the fact that one of the components of the posterior likelihood function is the sample likelihood function, for which, the range of observations (earthquake magnitudes) depends on the unknown parameter Mmax. This dependence violates the condition of optimal properties of the maximum likelihood estimators. The resulting likelihood function therefore reaches its maximum at the maximum observed magnitude, not at the required maximum possible magnitude Mmax. A possible correction to the current EPRI procedure is also presented. ReferencesCornell, C.A. (1994). Statistical analysis of maximum magnitudes in the earthquakes of stable continental regions, Vol. 1, Ed. J. Schneider, pp. 5-1-5-27, EPRI, Palo Alto, Calif., 1994. NP-4726. Seismic hazard methodology for the Central and Eastern United States. “The Earthquakes of Stable continental Regions. Vol. 1. Assessment of large Earthquake Potential.”
Session:Earth Structure Observations and Theory
Presenter   Goda, Katsuichiro
Schedule   Thu 11:00 AM / Oral
Room   Ballroom E
Variability of spatial correlation of peak ground motions and response spectra
GODA, K., University of Bristol, Bristol, Avon, United Kingdom, katsu.goda@bristol.ac.uk
Correlated seismic effects cause acute concentration and accumulation of seismic losses, potentially resulting in a catastrophic event. Therefore, spatial correlation models of peak ground motions and response spectra are key components for extending current probabilistic seismic hazard and risk analyses for a single location into those for multiple locations. The applications of the correlation models are broad, including seismic loss estimation of spatially-distributed buildings and infrastructure, insurance portfolio analysis of residential properties, and ShakeMap interpolation. The author has developed such correlation models using ground motion data from the PEER-NGA database, K-NET and KiK-net databases, and SK-net database (Goda and Hong, 2008; Goda and Atkinson, 2009, 2010; all are published in BSSA). One of the critical problems that have not yet been addressed is variability of the spatial correlation for different seismic events (i.e. inter-event variability of spatial correlation). Statistical analyses that were conducted by the author previously indicate that the overall spatial correlation model is accompanied by significant variability. This study will address this issue. For this, the mentioned ground motion databases are combined to form a consolidated database (note: the combined dataset has relatively rich data coverage at short separation distance range, where most of the existing studies lack dense data points). Results will highlight the extent and source of the spatial correlation variability, which needs to be incorporated in seismic hazard and risk calculations, and will provide useful guidance as to which aspects one should probe into to improve the assessment.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Kim, Kwang-Hee
Schedule   Wed AM / Poster
Room   Ballroom B
Crustal-scale seismogenic structure of the major collision boundary in the southeastern Taiwan
KIM, K. H., Korea Ocean Research and Development Institute, Ansan, Gyeonggi-do, Republic of Korea, kwanghee@kordi.re.kr; CHEN, K. C., Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ; CHIU, J. M., Center for Earthquake Research and Information, Memphis, TN, ; YEN, H. Y., National Central University, Jhongli, Taiwan, ; KANG, S. Y., Korea Ocean Research and Development Institute, Ansan, Gyeonggi-do, Republic of Korea, ; SUK, B. C., Korea Ocean Research and Development Institute, Ansan, Gyeonggi-do, Republic of Korea,
Longitudinal Valley (LV) is the surface representation of the plate collision and characterized by its narrow and long topographic features. Due to the oblique convergence of the Philippine Sea plate with respect to the Eurasian plate, it is widely considered the collision is in its initial stage in the southern LV and Coastal Range (CR). We explored the lateral variations of the subsurface structure due to the initiation of active collision using 3-D Vp and Vs models and relocated seismicity. High-resolution 3-D Vp and Vs models are determined using data collected by an island wide seismic network and a high-density temporary seismic network. We observe very complex structures with large lateral and vertical variations of seismic property in the study area. Velocity perturbations at shallow depths are largely corresponding to the variations in the surface geology. Velocity anomaly beneath the LV and the CR is characterized by a strong negative anomaly, which may represent the unconsolidated thick sediments observed at the surface. The overall distributions of velocity perturbations at mid-crustal depths (~16 km) are quite different from those observed in the slice views at the shallower depth. A narrow and long linear positive velocity anomaly is noticeable beneath the LV and its southern extension. In the east of the high velocity zone, another linear feature with low velocity perturbation is observable and sub-parallel to the previously mentioned high velocity anomaly. At deeper depths (>22 km) the low velocity perturbation beneath the Central Mountain Range is still the dominant feature. A high-velocity trend running northeast-southwest beneath the CR is present. Apparently it is continued from the high velocity anomaly observed in the mid-crustal depth slice. In general features in the mid-crustal depth extend to the deeper depths.
Session:Earth Structure Observations and Theory
Presenter   Kang, Su Young
Schedule   Thu PM / Poster
Room   Ballroom B
Relationship between DEM Resolutions and Site Classification in Korea
KANG, S. Y., Korea Ocean Research and Development Institute, Ansan, Gyeonggi-do, Korea, sukang@kordi.re.kr; KIM, K. H., Korea Ocean Research and Development Institute, Ansan, Gyeonggi-do, Korea, kwanghee@kordi.re.kr
Slope data derived from DEM can be an important indicator for site classification. It can be various due to the use of different resolutions of DEMs. We studied that resolutions may effect to the results of the site classification. We used 1, 3, 6, 9, ~ 27, 30 arc-sec DEM resolutions to illustrate deviations in the site classifications. 1 arc-sec DEM is from ASTER GDEM made by METI and NASA. Other maps are resampled from 1 arc-sec DEM for this study. DTED Level 0 is made by NIMA and USGS. We limited the study area into the south-eastern Korea to save the analyzing time occurring due to the size of the data. As the results, the largest difference within the site classification categories considering each resolution is site C (very dense soil and soft rock). If we reclassify the sites with Vs30 range by the slope criteria, less than 180 m/sec area has the largest difference. In the high resolution map, the areas with the stiffest and the modest gradient have been bigger than those shown on the low resolution map. But, other areas in the low resolution map are bigger than in the high resolution map. In the low resolution, it is resulted overestimated or underestimated because differences of slopes are averaged in the same grid. On the other hand, those areas in the high resolution are illustrated well. Also, site classification by slope has been agreed with borehole site classification result from 52% to 78%. The rate of concordance between Tg sites and the result from the high resolution is higher than from the low resolutions. Thus, the usage of higher resolution of DEM is better to characterize the rugged areas in Korea to improve the site classification results. Finally, the site classification considering higher resolution of DEM will provide useful information for the further study of regional hazard estimation, risk management, and other seismological and geotechnical applications as well as land use planning in developing areas.
Session:Archeoseismology: Learning about Ancient Earthquakes from the Archeological Record
Presenter   Schreiber, Stephan
Schedule   Fri 9:15 AM / Oral
Room   Ballroom D
Archeoseismological Investigations in the Historic Center of Cologne, Germany
SCHREIBER, S., University of Cologne, Seismological Station Bensberg, Bergisch Gladbach, Germany, stephan.schreiber@uni-koeln.de; HINZEN, K. G., University of Cologne, Seismological Station Bensberg, Bergisch Gladbach, Germany,
Since the first scientific studies of earthquake effects obvious in archeological findings some 100 years ago, the mode of operation has changed from a single- to a multidisciplinary approach. In addition to the cooperation of different disciplines the application of quantitative methods had a positive impact on solving archeoseismological problems.During the construction of an underground museum in the city center of Cologne (Germany), the Archeological Zone Cologne (AZC), parts of the Roman and medieval city are being excavated. The remains exhibit structural damages over an area of 150 x 200 m. Parts of these damages on the praetorium, the main building of the AZC, have been described before and the possibility of a secondary seismogenic origin was proposed. The current excavations allow additional investigations. The recently excavated remains together with sections excavated in 1954 were mapped with a 3D-laserscanner. The data were collected in over 200 individual scans and merged to models of the discrete buildings. These models are used to identify, classify and quantify the damages. The deformations of a Roman well and a medieval cesspit were investigated in detail by measuring the orientation of the moved building blocks. The models of the praetorium and of adjacent buildings were used to measure the distribution of tilt throughout the AZC. These investigations result in a complex damage pattern of the area. In a second step the underground of the AZC was investigated under geological and geotechnical aspects. Data from fieldwork and core pilings of the area were combined with information from borings and archeological excavations of the whole city area into a surface model of the Roman city. This model was used to create cross sections for a finite element model of the subsurface to test the behavior under static and dynamic loading.The presented approach allows the investigation of damages on archeological remains on the basis of quantified damage data.
Session:Assessment of Seismic Hazard from Paleoliquefaction Studies
Presenter   Bezerra, Francisco
Schedule   Fri 11:00 AM / Oral
Room   Ballroom D
Evidence of earthquake-induced soft-sediment deformation in late Quaternary alluvial gravels in the Potiguar Basin, Brazil
BEZERRA, F. H., University of Rio G Norte, Natal, RN, Brazil, bezerrafh@geologia.ufrn.br; MOURA-LIMA, E. N., University of Rio G Norte, Natal, RN, Brazil, elissandramoura@yahoo.com; DO NASCIMENTO, A. F., University of Rio G Norte, Natal, RN, Brazil, aderson@geofisica.ufrn.br; FERREIRA, J. M., University of Rio G Norte, Natal, RN, Brazil, joaquim@geofisica.ufrn.br
We present evidence of soft-sediment deformation in the Quaternary record of northeastern Brazil, South American intraplate. The region has experienced earthquake swarms that can last 10 years, and events that can reach 5.2 mb. We studied the Quaternary record of the Potiguar Basin, a Cretaceous to Cenozoic trough generated during the South Atlantic opening. The basin is located in a semi-arid area, where the Quaternary sediments are transported by seasonal floods and the valleys are characterized by river gradients lower than 1% and by ephemeral streams. Sediments are usually oxidized owing to the dry conditions, and therefore contain little or no organic matter outside the estuaries and deltas. The most common type of Quaternary alluvial deposits are gravelly and sandy braided sediments, some of which represent abandoned channels, whose grain sizes range from bolder to clay, with sand and pebbles being the most common. We carried out direct outcrop investigation or ground penetrating radar (GPR) surveys in more than 100 sites. Our study indicates that soft-sediment deformation structures occur in several alluvial-channel deposits. The shaking of sediments caused the collapse and realignment of pebbles, and generated pockets and dome-like load structures in a subaqueous alluvial channel system. Pockets and dome-like load structures formed as the water-sand mixture migrated upwards, causing a sudden downward accommodation of pebbles. We interpret these structures as the result of seismically-induced shaking of sediments in a reverse density gradient system. Optically Stimulated Luminescence (OSL), and Infrared Stimulated Luminescence (IRSL) methods following Multiple Aliquot Regeneration (MAR) and Single-Aliquot Regenerative-dose (SAR) protocols indicate that deformation occurred at least six times from ~400 ka to ~9 ka. These structures are similar to modern examples of seismically-induced soft-sediment deformation in gravels.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Stephenson, Randell
Schedule   Thu 3:30 PM / Oral
Room   Ballroom C
Intraplate Stresses and Strains
STEPHENSON, R. A., University of Aberdeen, Aberdeen, Scotland, United Kingdom, r.stephenson@abdn.ac.uk; NIELSEN, S. B., Aarhus University, Aarhus, Denmark, sbn@geo.au.dk
Significant intraplate deformations, including major faulting as well as folding as well as profound vertical motions on a sub-regional scale, are ubiquitous in the geological record – for example, as “inverted” sedimentary basins. This kind of intraplate deformation is directly related to “far-field” tectonic forces produced at plate boundaries. However, in many intraplate settings, the stress field can be dominated by contributions from surface topography and lateral density variations within the lithosphere. This results in lateral variations of lithospheric potential energy, the gradient of which is a source of stress. Intraplate stresses thus derived can induce elastic deformations but are generally not sufficient to cause significant plastic deformation such as thrusting or folding, as observed in inverted basins. Sub-regional (say at the scale of the New Madrid seismic zone) vertical motions can be purely elastic, however, and can result in important geological events clearly observed in the stratigraphic record. The magnitude and therefore significance of these depends on the presence of pre-existing stress states associated with specific legacy structural heterogeneities within the intraplate lithosphere. Geologically rapid plate boundary reorganisations can lead to geologically rapid changes to the intraplate stress field and, hence, to geologically sudden uplift or subsidence of sub-regional scale structures. Folding and faulting, in contrast, represent plastic responses to stress – deformation is non-recoverable – and probably only can be achieved when legacy thermo-structural heterogeneities within the intraplate lithosphere are such that the stress field is favourably perturbed vis-à-vis some pre-existing rheological variability. Subtle lateral variations in mechanical and/or thermal structure can result in rheological effects profound enough to lead to significant strain localisation and plastic deformation such as faulting.
Session:Archeoseismology: Learning about Ancient Earthquakes from the Archeological Record
Presenter   Hinzen, Klaus-G.
Schedule   Fri 9:30 AM / Oral
Room   Ballroom D
Earthquake versus Rockfall, Testing two Damaging Scenarios for a Roman Mausoleum
HINZEN, K. G., Cologne University, Bergisch Gladbach, Germany, hinzen@uni-koeln.de; KEHMEIER, H., Cologne University, Bergisch Gladbach, Germany, ; SCHREIBER, K. S., Cologne University, Bergisch Gladbach, Germany,
A Roman mausoleum located in the ancient city of Pınara, southwest Turkey, shows clear signs of damages due to dynamic action. The heavy damages include fallen blocks from the top of the building and wall deformations of several decimeters; however, most parts of the building are still standing. This setting is better than totally demolished structures for an archaeoseismic analysis. Considering the seismotectonic potential of the area, earthquake ground motions are a possible cause of the damages. However, the building is located at the foot of an 80 m high cliff with a significant rock fall hazard, confirmed by numerous boulders found in the range between cliff and the structure. We present a 3D discrete element model of the mausoleum based on a 3D laser scan. The model consists of 180 rigid blocks with a total mass of 180 tons. The range of impact velocities of blocks of different size and form and the actual slope of the cliff have been incorporated into 2D model calculations. The deformations caused by simulated impacts are compared to the actual displacements of blocks quantified from the laser scan. In addition, analytic ground motions signals are used to study the principal reaction of the building. A second damage scenario with earthquake strong ground motion records simulates realistic 3D earthquake loadings.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Atkinson, Gail
Schedule   Wed 8:30 AM / Oral
Room   Room 204/205
Attenuation Issues for the Development of Ground-Motion Prediction Equations in Eastern North America
ATKINSON, G. M., University of Western Ontario, London, ON, Canada,
A key issue in the development of ground-motion prediction equations (GMPEs) for central and eastern North America (ENA) concerns the attenuation of earthquake ground motions. There are significant uncertainties concerning how the attenuation rate may change with distance, considering contributions of direct-wave phases, Moho bounce effects, and Lg propagation at regional distances – and how best to characterize these effects for GMPEs. The attenuation rate near the source is particularly uncertain, due to the paucity of near-source ground-motion data. Furthermore, the attenuation may vary regionally or with focal depth. This study uses the current ENA database to overview these issues in an empirical context, comparing ground-motion data to a variety of published functional forms and attenuation rate functions. I conclude that the average attenuation shape, over many events, may be fit by a linear, bilinear or trilinear shape model. The attenuation curve for an individual event may differ significantly from the ensemble average. There are trade-offs between geometric and anelastic attenuation, and these impact conclusions regarding attenuation shape and source parameters. Statistically, there is strong evidence that the best-fit attenuation model in ENA is trilinear, at least at low frequencies, with the transition zone due to Moho bounce effects exerting a significant influence on the shape of the attenuation curve in the distance range from 70 to 140 km. There is also strong evidence for attenuation steeper than 1/R at near distances (R<70 km). Nevertheless, a simple 1/R geometric spreading model at all distances and frequencies (with an associated Q~2000) does as well as any model in providing (on average) low bias at near-source distances, while being pegged by the amplitude levels observed at regional distances. A 1/R model thus makes a simple and attractive choice for GMPE development.
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Pasyanos, Michael
Schedule   Thu 9:45 AM / Oral
Room   Ballroom E
Developing an Updated Global Crust and Upper Mantle Model using Multiple Data Constraints
PASYANOS, M. E., Lawrence Livermore National Laboratory, Livermore, CA, pasyanos1@llnl.gov; MASTERS, T. G., IGPP, University of California, San Diego, CA, tmasters@ucsd.edu; LASKE, G., IGPP, University of California, San Diego, CA, glaske@ucsd.edu; MA, Z., IGPP, University of California, San Diego, CA, z1ma@ucsd.edu
Models such as CRUST2.0 (Bassin et al., 2000) have proven very useful to many seismic studies. We are in the process of developing an updated, higher resolution model called LITHO1.0 that extends deeper to include the lithospheric lid. The model is evolving away from the crustal types strongly used in CRUST5.1 (Mooney et al., 1998) to a more data-driven model. This is accomplished by performing a targeted grid search with multiple data inputs. We seek to find the most plausible model which is able to fit multiple constraints, including updated sediment and crustal thickness models, upper mantle velocities derived from travel times, and surface wave dispersion. The latter comes from a new, very large, global Rayleigh wave group velocity dataset built using a new, efficient measurement technique that employs cluster analysis (Ma et al., 2011). We will discuss datasets and methodology, and show preliminary results for an isotropic model for a limited region. A global model, which will incorporate anisotropy, will be developed when the global Love wave dataset is available.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Harrison, Richard
Schedule   Thu 10:45 AM / Oral
Room   Ballroom C
Deformation in the Thebes Gap Area Revisited: Old Lessons on Long-term Tectonism in the Midcontinent, United States
HARRISON, R. W., USGS, Reston, VA, rharriso@usgs.gov
Thebes Gap (TG) is the closest locality to the New Madrid seismic zone (NMSZ) where rocks of Paleozoic thru Cenozoic age crop out and strain can be observed directly in the field. TG overlies NE-trending Commerce geophysical lineament, which has roots in the Proterozoic basement and is parallel to NMSZ. Thus, the strain history at TG can be used as a proxy for NMSZ. Far-field dextral strike-slip on vertical NE-striking faults of Ordovician (Taconic) age is the oldest strain at TG. During the Late Paleozoic Ouachita orogeny, these faults were reactivated under N-S stress as left-lateral faults, conjugate to the NW-trending Pascola arch. Dextral faulting during Late Paleozoic Allegheny orogeny occurred, with as much as 300 m of slip on one structure. Far-field deformation related to the Laramide orogeny also is documented. At least four episodes of faulting have occurred at TG in the Late Quaternary. Dextral strike-slip faulting occurred post-Sangamon Geosol, pre- Roxana Silt (~55to 40 ka), and post-Roxana, pre-Peoria Loess (~28-25 ka). 14C ages on fault-wedge colluvium indicate faulting occurred at ~ 5,606 ± 169 and 1,179 ± 107 yrs BP on some structures. The 28-25 ka episode is anomalous in that it indicates NW-SE to NNE-SSW compression, at right angles to other Neogene stresses and present-day regional stress field of ENE-WSW compression. The TG strain history suggests that vertical, deep-seated faults in the midcontinent U.S. are subject to reactivation under far-field stresses derived from plate-margin collisional events. In the absence of such events, the Quaternary strain history suggests additional drivers. Possibilities include glacial loading and unloading stress mechanisms, suggested from the timing of resolved deformation, or intraplate stresses related to North American plate motion that are reactivating major basement structures periphery to the stable craton.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Van Arsdale, Roy
Schedule   Wed 11:15 AM / Oral
Room   Ballroom C
Geologic History of the New Madrid Seismic Zone Region
VAN ARSDALE, R. B., University of Memphis, Memphis, TN, rvanrsdl@memphis.edu
The basement structure of the New Madrid seismic zone (NMSZ) region is dominated by the NE trending Reelfoot rift normal faults. This early Cambrian rift was superimposed on NW trending Proterozoic faults resulting in a basement of fault bounded blocks. Rift fill culminated with a thickened section of the regionally extensive Ordovician Knox carbonates. The rift was lifted to form a NE trending arch during the middle Cretaceous as a consequence of the North American plate passing over the Bermuda hotspot. Erosion of the arch, and subsidence of the region upon crustal cooling, resulted in formation of the Mississippi Embayment in late Cretaceous and early Tertiary. One of the major structures of the NMSZ is the NW trending Reelfoot reverse fault. The Reelfoot fault and its associated rift parallel faults are linked and thus have a common history. Quaternary NMSZ fault movement is interpreted to be due to an alteration of the local stress field by entrenchment of the Mississippi River. Quaternary faulting has resulted in liquefaction, landslides, and landscape changes. However, tectonic landforms and Quaternary faulting extend beyond the footprint of the NMSZ seismicity to include additional faults of the Reelfoot rift in the Benton Hills of MO, the southeastern Reelfoot rift margin of TN, and faults south of the NMSZ in southeastern AR. The NMSZ may represent a relatively short lived and local fault activation that moves through time among the Reelfoot rift faults.
Session:Assessment of Seismic Hazard from Paleoliquefaction Studies
Presenter   Holzer, Thomas
Schedule   Fri 10:30 AM / Oral
Room   Ballroom D
Regional Peak Ground Acceleration During the 1811-12 New Madrid Earthquakes Inferred from Paleoliquefaction in Quaternary Sediments
HOLZER, T. L., U.S. Geological Survey, Menlo Park, CA, tholzer@usgs.gov; NOCE, T. E., U.S. Geological Survey, Menlo Park, CA, tnoce@usgs.gov; BENNETT, M. J., U.S. Geological Survey, Menlo Park, CA, mjbennett@usgs.gov
Both the regional pattern and magnitudes of peak ground accelerations (PGA) caused by the 1811-1812 New Madrid earthquakes were inferred from surficial paleoliquefaction features in Quaternary sediments in the Mississippi embayment of Arkansas and Missouri. PGA was inferred within the 11,000 km2 area that is partially covered by surface manifestations of liquefaction. Surface manifestations include sand blows and sand-filled lateral spreading and ground cracks. PGA estimates were derived from liquefaction probability curves, which relate the percentage of land affected by liquefaction to a magnitude-scaled PGA (Holzer and others, 2011, Environmental and Engineering Geoscience). Probabilities were based on complementary cumulative frequency distributions of the liquefaction potential index (LPI), which were computed with 258 cone penetration test soundings that were conducted in the surficial geologic units mapped by Saucier (1994, U.S. Army Corps of Engineers) and that exhibit paleoliquefaction features. The magnitude-scaled PGA was computed by dividing PGA by the liquefaction magnitude scaling factor (MSF). Both a moment magnitude and water table depth are required for the analysis. We considered uncertainty in MSF and the potential impact of sand aging because approximately 64 % of the mapped liquefaction area in the embayment is underlain by Late Pleistocene valley train (braid belt) deposits. We infer that the maximum PGA ranged from 0.20 to 0.46 g, depending on the assumed magnitude, MSF, water table depth, and effect of sand aging. The low values of PGA are consistent with ground motions predicted with published ground motion prediction equations for rock when these motions are corrected for local site effects. The local-site correction, which was based on the measured average shear-wave velocity (VS30= 220 ± 15 m/s) in the liquefaction area, indicates PGA’s were significantly deamplified in the embayment in 1811-1812.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Hamburger, Michael
Schedule   Thu 4:30 PM / Oral
Room   Ballroom C
Seismicity and Active Crustal Deformation in the New Madrid and Wabash Valley Seismic zones: Where’s the Missing Link?
HAMBURGER, M. W., Indiana University, Bloomington, IN, hamburg@indiana.edu; GALGANA, G. A., Lunar and Planetary Institute, Houston, TX, ggalgana@lpi.usra.edu; JOHNSON, K. A., Indiana University, Bloomington, IN, kajjohns@indiana.edu
We compare geodetic and geophysical data for the Wabash Valley Seismic Zone (WVSZ) of southern Indiana and Illinois and the New Madrid Seismic Zone (NMSZ) of the Mississippi Valley. Both intraplate seismic zones are characterized by high-angle faults that define Precambrian grabens underlying relatively undeformed Phanerozoic rocks. They are separated by an enigmatic tectonic zone characterized by basement uplift, Precambrian strike-slip and normal fault zones, and Mesozoic and Cenozoic magmatism. We examine present-day deformation in the two zones as measured by campaign and continuous GPS networks. The average strains for the entire network show marginally significant strain rates, with NW-SE compressive strain whose orientation is rotated ~45° from the pervasive regional stress direction. We examine models that test the effect of the 1811-1812 New Madrid earthquakes on the near- and far-field strain and seismicity rates in the region through instantaneous elastic deformation in the lithosphere and associated postseismic viscoelastic flow in the asthenosphere. Our results indicate that significant changes in strain and seismicity rates in the WVSZ can persist for several hundred years following the New Madrid earthquakes. The seismicity rate can increase by as much as 7x the background rate in the near-field, but by a much smaller amount in the far-field, with modeled seismicity rates highly dependent on the choice of lower-crust viscosity. We also investigate the possibility that the New Madrid earthquakes could modify seismicity or strain in the WVSZ by producing trigger¬ed slip on a buried fault in the Illinois Basin region. Our initial results demonstrate that elevated seismicity and strain in the WVSZ could result from aseismic slip triggered by viscous relaxation in the lower crust long after the New Madrid earthquakes. Similarly, time-varying strains in both regions could be governed by isostatic adjustment due to Holocene deglaciation of North America.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Holzer, Thomas
Schedule   Thu 9:45 AM / Oral
Room   Room 204/205
Probabilistic Liquefaction Hazard Mapping Efforts in the San Francisco Bay Area, California, and Future Needs
HOLZER, T. L., U.S. Geological Survey, Menlo Park, CA, tholzer@usgs.gov; BENNETT, M. J., U.S. Geological Survey, Menlo Park, CA, mjbennett@usgs.gov; NOCE, T. E., U.S. Geological Survey, Menlo Park, CA,
The M7.8 1906 San Francisco earthquake provided one of the earliest demonstrations of the hazardous consequences of earthquake-induced liquefaction when damage to waterlines contributed to the inability to suppress the postearthquake fire. Despite this experience, susceptible sandy fills continued to be placed into San Francisco Bay until the mid-1960’s. Prompted in 1998 by this history and a Federal/local government partnership, Project Impact, the USGS developed and applied a probabilistic method for liquefaction hazard mapping. The method relies on the liquefaction potential index (LPI) to characterize the spatial variability of geologic deposits. In the Bay area, we have relied on the cone penetration test (CPT) both to determine and calibrate LPI values. The mapping methodology was first applied to the greater Oakland area using a constant ground motion for two scenario earthquakes on the Hayward Fault. With the refinement of GIS software, the performance of post-1906 sandy fills in the East Bay was evaluated for a repeat of the 1906 San Francisco earthquake with consideration of spatially variable ground motion, local site effects, and uncertainty in ground motion predictions. In 2008, maps of the Santa Clara Valley were completed that considered multiple earthquake scenarios as well as the impact of different water table depths. These prototype mapping efforts reveal several needs and priorities for future research: (1) improvement in the ability to recognize and characterize marginally liquefiable soils with the CPT; (2) development of geotechnical aging corrections for Early Holocene and older liquefiable sands; (3) geotechnical characterization of soils in the context of geologic units; (4) integration of standard penetration test data with CPT data to improve assessments of liquefaction potential; (5) accurate regional maps of depths to ground water; and (6) validation of hazard maps with historic observations.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Galgana, Gerald
Schedule   Thu 4:15 PM / Oral
Room   Ballroom C
A Decade of Geodesy and Active Intraplate Tectonics in the Wabash Valley Seismic Zone: Are we there yet?
GALGANA, G. A., Lunar and Planetary Institute, USRA, Houston, TX, galgana@lpi.usra.edu; HAMBURGER, M. W., Dept. of Geological Sciences, Indiana University, Bloomington, IN, hamburg@indiana.edu; JOHNSON, K. M., Dept. of Geological Sciences, Indiana University, Bloomington, IN, kajjohns@indiana.edu
We present observational and geodynamic modeling results based on GPS geodetic campaigns within the Wabash Valley seismic zone, a seismically active intraplate region situated in southern Illinois, western Kentucky and southwestern Indiana. The observed velocity field from a 56-station campaign-based regional GPS network shows systematic motion of network sites with respect to the Stable North American Reference Frame at 1-2 mm/yr in a N-NE direction. We observe a similar ~1-3 mm/yr general northward trend of the velocity field of the dense 35-station campaign network in the Fluorspar district, Shawnee National Forest of southern Illinois, a transitional region between the Wabash and New Madrid seismic zones. We combine the observed campaign velocity fields with subsampled site observations from existing continuous GPS networks within the region using elastic block models. We find that multiple block models can characterize the regional deformation field through: (1) a rigid, four-block system with elastic strain along planar faults (i.e., the Cottage Grove-Rough Creek fault system and the Wabash Valley fault system); or, alternatively (2) a region comprised of several internally deforming blocks; A model describing the area as a single deforming region shows 1.4 ± 0.7 ns/yr NW-SE compression, and 1.6 ± 0.6 ns/yr NE-SW extension. The Shawnee region deforms with 2.4 ± 2.7 ns/yr E-W compression and 3.4 ± 2.3 ns/yr N-S extension. While the strain rate estimates remain close to the resolution of GPS measurements, the systematic north-trending velocities and systematic internal strain suggest several possible tectonic interpretations of the surface deformation: slow strain accumulation associated with glacio-isostatic adjustment, long-term post-seismic deformation triggered by the 1811-1812 New Madrid earthquakes, and motions arising from relatively rigid but “jostling” tectonic blocks associated with intraplate strains.
Session:Earth Structure Observations and Theory
Presenter   Bao, Xueyang
Schedule   Thu PM / Poster
Room   Ballroom B
Crustal Seismic Attenuation Study in Eastern Tibetan Plateau: Reverse Two-station/event Method, Q Azimuthal Anisotropy, and Intrinsic Q Approach
BAO, X., University of Missouri, Columbia, MO, xbqzb@mail.missouri.edu; SANDVOL, E. A., University of Missouri, Columbia, MO, sandvole@missouri.edu; NI, J., New Mexico State University, Las Cruces, NM, jni@nmsu.edu; HEARN, T., New Mexico State University, Las Cruces, NM, thearn@nmsu.edu; CHEN, J., Peking University, Beijing, China, johnyc@pku.edu.cn; SHEN, Y., University of Rhode Island, Narragansett, RI, yshen@gso.uri.edu
The intrinsic Q calculated from Lg is a proxy for crustal Qs and can be used to infer the rheology and tectonics of the Tibetan Plateau crust. The waveform data used in this study are from a wide variety of permanent and temporary networks including CDSN, Namche Barwa, MIT-China, ASCENT, INDEPTH-IV-UK, and NETS. We use a Reverse Two-station/event Method (RTM) to measure interstation QLg, which theoretically eliminates effects from the source, radiation pattern, and site response. We observe a strong correspondence between the lowest QLg and major active strike slip faults within the plateau. The measured RTM QLg has azimuthal anisotropy with a 1/Q~cos2A relationship, which most probably represents the large-scale variations and discontinuity of seismic velocity controlled by deformation patterns within the plateau. The low 1/Q directions parallel the major fault planes and the anisotropic magnitudes are stronger in northern Tibet, which approximately correlates with shear wave splitting and surface wave azimuthal anisotropy measurements. The isotropic 1/Q is used to solve intrinsic Q based on the model of Dainty (1981) and the experiment of Kampfmann and Berckhemer (1985), which further isolates the nearly isotropic small-scale scattering attenuation. We have used these approached to obtain tomographic images of intrinsic Q and its frequency dependence, the scattering Q, and the ratio of intrinsic Q and scattering Q within Eastern Tibetan Plateau. We observe that the intrinsic frequency dependence is approximately 0.25 in the whole region, which is consistent with the result of laboratory experiments. The scattering plays an equal role to the intrinsic attenuation in the Qaidam Basin and the Lhasa Block, south of the BNS. The intrinsic attenuation is dominant in northern Tibet with Q values of less than 200 in the central Qiangtang Terrane, which implies a hot (probably higher than 750°C) and possibly partially molten crust that is consistent with other studies.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Andrews, Dudley Joe
Schedule   Wed 9:00 AM / Oral
Room   Ballroom E
Specifying Initial Stress for Dynamic Heterogeneous Earthquake Source Models
ANDREWS, D. J., U. S. Geological Survey, Menlo Park, CA, jandrews@usgs.gov; BARALL, M., U. S. Geological Survey, Menlo Park, CA, mbinv@invisiblesoft.com
Dynamic rupture calculations, using heterogeneous stress drop that is random and self-similar, with a power-law spatial spectrum, have great promise of producing realistic ground motion predictions. We present procedures to specify initial stress for random events with a target rupture length and target magnitude. The stress function is modified in the depth dimension to account for the brittle-ductile transition at the base of the seismogenic zone. Self-similar fluctuations in stress drop are tied in this work to the long-wavelength stress variation that determines rupture length. Heterogeneous stress is related to friction levels, in order to relate the model to physical concepts. In a variant of the model, there are high stress asperities with low background stress. This procedure has a number of advantages. (1) Rupture stops naturally, not at artificial barriers. (2) The amplitude of short-wavelength fluctuations of stress drop is not arbitrary; the spectrum is fixed to the long-wavelength fluctuation that determines rupture length. (3) Large stress drop can be confined to asperities occupying a small fraction of the total rupture area, producing slip distributions with enhanced peaks.
Session:Verification Science
Presenter   Heyburn, Ross
Schedule   Fri 3:45 PM / Oral
Room   Room 204/205
Making the Most of Body and Surface Wave Observations to Estimate Earthquake Source Depths
HEYBURN, R., AWE Blacknest, Brimpton Common, Reading, Berkshire, U.K., ross@blacknest.gov.uk
In detailed seismological studies of small-to-medium sized (4 < mb < 5.5) earthquakes, observations from different types of seismic data can be analysed to obtain estimates of the source depth. For example, source depths can be estimated by identification of the teleseismic depth phases pP and sP, or by modeling surface wave amplitude spectra. In this study the sensitivity of these methods to the focal mechanism and the recording station locations are examined, and examples are shown where observations from both data types can be combined to help estimate the source depth. Source radiation patterns show that for some source mechanisms, the predicted amplitude of the teleseismic depth phase pP will only be large at a limited range of distances and azimuths, and the Rayleigh wave spectral nulls that tightly constrain the source depth when modeling surface wave amplitude spectra often only occur for a limited range of azimuths. For earthquakes where Rayleigh wave spectral nulls are not observed and the source depth cannot be constrained using the surface wave amplitude spectra alone, the focal mechanism obtained by modeling Rayleigh and Love wave amplitude spectra can be used to predict the locations of stations where pP should have a large amplitude and can be easily picked by an analyst even when direct P may be weak. The increased global coverage of seismometer stations means that there is an increased likelihood that stations exist in the locations where the predicted amplitude of pP is large. As depth phases identified in this way are consistent with the source mechanism, this approach allows increased confidence to be placed in the estimated source depth.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Wang, Zhenming
Schedule   Fri AM / Poster
Room   Ballroom B
A Case Study on Probabilistic Methods in Seismic Hazard Assessment: Probabilistic Seismic Hazard Analysis
WANG, Z., University of Kentucky, Lexington, KY, zmwang@uky.edu
Any geological or geophysical measurement has a certain degree of uncertainty. For example, an earthquake reported to be Mw7.0 by one institution, may be reported to be Mw7.1 by another institution. Thus, probabilistic methods are necessary tools for quantifying geological and geophysical parameters. This is particularly true for seismic hazard assessment. The purpose of a seismic hazard assessment is to quantify ground-motion parameters, including associated uncertainties, at a site of interest from instrumental, historical, and geological observations. Caution must be exercised, however, when applying a probabilistic method for seismic hazard assessment because the assumptions and conditions associated with the chosen method may not be applicable or valid. For example, although probabilistic seismic hazard analysis (PSHA), which was developed from a rigorous probability analysis on distributions of earthquake magnitudes, locations, and ground-motion attenuation relationship, has become the most widely used probabilistic method in seismic hazard assessment, it has been found that some of the assumptions and preconditions inherent to PSHA are not be applicable or valid. These inapplicabilities or invalidities have led to serious problems such as the extreme high and unphysical ground motion estimates from applying PSHA. In addition, efforts must also be spent on how to communicate the results from a seismic hazard assessment.
Session:Ground Motion Scaling and Selection
Presenter   Wang, Zhenming
Schedule   Fri 10:45 AM / Oral
Room   Room 204/205
Ground Motion Time Histories for Seismic Design of Bridge and Highway Structure in Kentucky
WANG, Z., University of Kentucky, Lexington, KY, zmwang@uky.edu
Ground motion time histories become more and more important in engineering seismic design and analysis, particularly for critical facilities such as bridge and highway structure. However, it may be difficult to obtain the time histories from observations in areas with low seismicity, such as the central United States. Thus, synthetic ground motion time histories become necessary alternatives for engineering design and analysis in the central United States. The synthetic ground motion time histories associated with the expected earthquakes (EE), probable earthquakes (PE), and maximum creditable earthquakes (MCE) were developed through a scenario seismic hazard assessment in Kentucky. EE is defined as the earthquakes that could be expected to occur any time in the bridge lifetime of 75 years. PE is defined as the earthquakes that could be expected to occur in the next 250 years. MCE is defined as the maximum event considered likely in a reasonable amount of time. The synthetic time histories were generated by using the composite source model which takes into account the source effects, including directivity and asperity, and path effects. Ground-motion parameters, such as peak ground acceleration and response spectra associated with the three earthquake scenarios were also developed and depicted in three sets of maps, peak ground acceleration and short period (0.2 s) and long period (1.0 s) response accelerations with 5 percent damping. These time histories, along with the maps, provide bases for performance-based seismic design and analysis of bridge and highway structure in Kentucky.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Holzer, Thomas
Schedule   Wed 10:30 AM / Oral
Room   Ballroom C
Implications of Liquefaction Caused by the 1811-12 New Madrid Earthquakes for Estimates of Ground Shaking and Earthquake Magnitudes
HOLZER, T. L., U.S. Geological Survey, Menlo Park, CA, tholzer@usgs.gov; NOCE, T. E., U.S. Geological Survey, Menlo Park, CA, tnoce@usgs.gov; BENNETT, M. J., U.S. Geological Survey, Menlo Park, CA, mjbennett@usgs.gov
Strong shaking during the 1811-1812 New Madrid earthquakes caused approximately 11,000 km2 in the Mississippi embayment of Arkansas and Missouri to be partially covered by sand ejected from underlying liquefied deposits. The liquefaction field presents an opportunity to infer seismological aspects of the earthquakes. We estimated ground shaking over the region by conducting 258 cone penetration test soundings in surficial geologic units and “reverse engineering” our method for probabilistic liquefaction hazard mapping (Holzer and others, 2011, Envir. and Eng. Geoscience). We infer that maximum peak ground acceleration (PGA) ranged from 0.20 to 0.46 g, depending on the assumed earthquake magnitude, liquefaction magnitude scaling factor, water table, and effect of sand aging. The low to moderate values of PGA are consistent with published ground motion prediction equations for rock when these motions are corrected for local site effects. The local-site correction, which was based on the measured average shear-wave velocity (VS30= 220 ± 15 m/s) in the liquefaction area, indicates PGA was significantly deamplified relative to rock in the embayment during the 1811-1812 earthquakes. Proposed moment magnitudes of the 1811-1812 earthquakes were evaluated by considering the intensity of the liquefaction features as a function of distance from the seismic source. Our evaluation suggests that the magnitudes were approximately middle sevens (~7.5), and are inconsistent with smaller magnitudes (<7).Penetration testing of geologic deposits that liquefied in 1811-1812 indicates that the liquefaction hazard in the embayment remains significant. A repeat of the 1811-1812 earthquakes could cause widespread disruption to the many lifelines that pass through the Upper Mississippi Valley. Dewatering of shallow deposits for agriculture, however, may have lowered water tables below 1811-1812 levels and thereby slightly reduced the liquefaction hazard.
Session:Verification Science
Presenter   Patton, Howard J
Schedule   Fri 4:30 PM / Oral
Room   Room 204/205
A Method to Infer Material Properties and mb Bias of the North Korean Test Site Using Yield : Depth-of-Burial Tradeoff Curves and {mb - Ms} Double Differences
PATTON, H. J., Los Alamos National Laboratory, Los Alamos, NMUSA, patton@lanl.gov
Yield versus depth-of-burial (W:h) tradeoff curves for the 2009 North Korea (NK) test show a systematic offset between determinations based on mb and isotropic explosion moment MI. The W:h curves also depend on the choice of cavity radius scaling model. The offset is attributed to combined effects due to mb bias NK and inaccurate values of source medium P wave speed NK and Poisson ratio NK required by theoretical scaling equations for MI. Constraint equations are developed for the tradeoff curves based on two widely-used scaling models. Another constraint equation is derived employing a modified formulation of {mb - Ms} double-differences due to Stevens and Day. Magnitudes for tests conducted on Pahute Mesa serve as calibration data for double-differences. Ranges of accepable parameter values satisfying (1) the constraint equations and (2) plausible bounds on NK and NK for intact granite, the medium in which the NK tests were likely conducted, are fairly narrow. For NK, NK, and NK, they are: ~0.08 - 0.15 mu, ~5400 - 6000 m/s, and ~0.17 - 0.19, respectively, using the scaling model of Heard and Ackerman employed by Mueller and Murphy. For Denny and Johnson scaling, they are ~0.16 - 0.26 mu, ~4900 - 6000 m/s, and ~0.265 - 0.275 . NK and NK are inversely correlated: the higher NK is, the lower the mb bias.
Session:Ground Motion Scaling and Selection
Presenter   Pezeshk, Shahram
Schedule   Fri 11:30 AM / Oral
Room   Room 204/205
Frequency-Domain Spectral-Matching Procedures
SHAHBAZIAN, A., Shannon and Wilson, Inc., Seattle, WAUSA, ; PEZESHK, S., The University of Memphis, Memphis, TNUSA, spezeshk@memphis.edu
The frequency domain spectral matching procedures are not new and have been developed in the last several decades. In these procedures, ground motion records from past events are modified in the frequency domain to be used in engineering analysis applications. In this presentation, we first present the concept of the record adjustment in the frequency domain and then displacement distortion issue caused by these methods is discussed. Spectral matching in the frequency domain with a multiplicative scale function applied to the Fourier spectrum requires a special attention in the matching process to have control on the displacement time history. This study shows that the velocity value at the end of the record is not affected by the Fourier amplitude spectrum scaling but the displacement may linearly increase boundlessly. Two numerical solutions are proposed to solve the displacement drift problem in the frequency domain. Following the proposed frequency domain base-line correction procedure, one does not need to perform base-line correction in the time domain after completing the spectral matching. As a result, acceleration, velocity, and displacement time histories will remain fully compatible and the boundary conditions of the velocity and displacement time histories will be preserved. We show that applying an appropriate window along with the zero-padding technique can lead to a reasonable displacement time history. The proposed procedures can be easily added to the existing or new frequency domain spectral matching algorithms without significantly disrupting the spectral matching process.
Session:Geotechnical Lessons Learned from Recent Earthquakes: Haiti, Chile, Baja CA, New Zealand
Presenter   Jeong, Seokho
Schedule   Fri 9:30 AM / Oral
Room   Room 204/205
Observations and Simulations of Topography Effects during the M7.0 Haiti Earthquake
JEONG, S., Georgia Institute of Technology, Atlanta, GA, lukesh13@gmail.com; ASSIMAKI, D., Georgia Institute of Technology, Atlanta, GA, dominic@gatech.edu; HOUGH, S., US Geological Survey Pasadena, Pasadena, CA, hough@gps.caltech.edu
Seismic hazard assessment and microzonation studies rely increasingly on wave motion simulations for the prediction of surface motion accelerations for given seismic input scenarios. By and large, ground motion simulations do not account for topographical features, making the assumption of a flat Earth surface model. Observations from large earthquakes, however, have shown that the presence of a strong topographic relief can significantly aggravate the catastrophic consequences of strong seismic motion. The effects of topography on site response cannot be predicted by the widely employed flat surface models; nor can they be predicted by any simple proxy-based approach. Wave motion simulation tools are required to identify topographic features that are associated with significant ground motion amplification. . We present a case study of topography effects from the M7.0 Haiti earthquake of 12 January 2010 that caused widespread catastrophic damage in Port au Prince as well as in cities to the west of the capital. We focus in the district of Petionville, south of central Port au Prince, where a large number of structures located along and atop a foothill ridge sustained serious damage or collapse that may not be attributed to their structural vulnerability alone. We employ idealized theoretical models and numerical simulations and show that the amplitude and predominant frequencies of observed amplification factors are consistent with predictions for the diffraction of elastic waves by ridge-type topographic features. Using available site characterization data, we also investigate the role of near-surface stratigraphy on further aggravating the topographic amplification of ground motion at frequencies of engineering concern
Session:Seismic Siting for Nuclear Power Plants
Presenter   Hardebeck, Jeanne
Schedule   Fri AM / Poster
Room   Ballroom B
Objective Determination of the Geometry of the Shoreline and Hosgri Faults, near Point Buchon, California, from Seismicity Relocations
HARDEBECK, J. L., U.S. Geological Survey, Menlo Park, CA, jhardebeck@usgs.gov; ZHANG, H., MIT, Cambridge, MA, ; THURBER, C. H., University of Wisconsin, Madison, WI,
Earthquake locations can illuminate fault structures at seismogenic depth, but their interpretation is often subjective as fault planes are usually interpreted from the earthquake locations by eye. The Optimal Anisotropic Dynamic Clustering (OADC) algorithm [Ouillon et al., JGR 2008] can be used to objectively identify the simplest fault geometry that fits all earthquakes to within the average location uncertainty. The average earthquake location uncertainty is the only parameter, and it is obtained objectively from the location algorithm. There are no parameters that can be tuned.We relocate ~100 earthquakes near Point Buchon using the double-difference program hypoDD [Waldhauser and Ellsworth, BSSA 2000]. Differential arrival times are found from waveform cross-correlation, and all waveforms are inspected for quality. We use the hypoDD SVD solver to obtain reliable location uncertainty estimates. We apply the OADC algorithm, with repeated runs to avoid local minima, and select the solution with the lowest RMS misfit to the earthquake locations.The best-fitting solution consists of just two planes, one corresponding to the Shoreline Fault and one to the Hosgri Fault. These planes are stable over all low-misfit solutions and across catalogs with different hypoDD parameters. The Shoreline plane is near vertical, while the Hosgri plane dips ~70° to the NE. The two planes meet at an angle of ~30°, like the seismicity. There is no objective evidence for any discontinuities or segmentation of the Shoreline Fault at seismogenic depths, as all earthquakes along its known length fall on a single plane to within the location uncertainty. Discontinuities smaller than the location uncertainty of ~1 km may be undetected, but would be too small to be barriers to earthquake rupture [Wesnousky, BSSA 2008]. The Shoreline plane is ~25 km long, and its NW end extends to the mapped trace of the Hosgri Fault, indicating that there is no gap between these faults at seismogenic depths.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Morozov, Igor
Schedule   Wed 3:30 PM / Oral
Room   Room 204/205
Alternate Models of Seismological Attenuation
MOROZOV, I. B., University of Saskatchewan, Saskatoon, SK, Canada, igor.morozov@usask.ca
Despite its unanimous acceptance and broad use in seismology, the concept of in situ medium Q appears to have little support in physics. A manifestation of a problem with this concept can be seen in Q values often increasing with frequency, and particularly being nearly proportional to it. Nevertheless, when approached directly from first physical principles, the attenuation of elastic-wave energy can be described without the use of Q or viscoelastic theory. In a macroscopic framework similar to Biot’s model of porous saturated rock, four general mechanisms of weak energy dissipation can be recognized: 1) dissipation due to internal degrees of freedom with kinetic coupling (such as pore fluids); 2) shear (dynamic) viscosity; 3) bulk viscosity; and 4) elastic scattering. The first three of these mechanisms correspond to the only three scalar invariants which are quadratic in velocity. Neither of these mechanisms is related to the elastic moduli of the medium, which remain “instantaneous” and real-valued. We argue that seismic attenuation can be better viewed as the dissipation of kinetic energy rather than as “imperfect elasticity.” Similarly, neither of the mechanisms 1) – 4) requires or leads to a consistent definition of a “medium Q.” The values of Q only arise as attributes of the resulting wave solutions, such as normal modes of the Earth’s free oscillations, various types of traveling waves, or stress-strain phase shifts in laboratory measurements. Such attributes cannot be considered as physically dependent on the frequency, and therefore the question of frequency dependence of Q also disappears.In view of the attenuation mechanisms above, a number of existing models of Q may need to be reconsidered. We illustrate several such models for surface waves and normal modes. Compared to the existing solutions, the models indicate an increased sensitivity to the near surface and greater ambiguity of inversion for the in situ attenuation parameters.
Session:Guide to Sustainable Seismographic Networks
Presenter   Havskov, Jens
Schedule   Fri 9:30 AM / Oral
Room   Ballroom C
Key to Sustainable Seismic Networks: Manpower and Skills More Important than Equipment
HAVSKOV, J., Department of Earth Science, University of Bergen, Bergen, Norway, jens@geo.uib.no; OTTEMOELLER, L., Department of Earth Science, University of Bergen, Bergen, Norway, lars.ottemoller@geo.uib.no
In many countries, both developing and developed, it is often easier to buy equipment than to obtain funding for sustained long-term operation. In practice, it happens that new systems, with overkill in instrumentation, get bought without the required skills to operate the network and to process the out-coming data, and without sufficient funding for operation. Experience shows that a maximum of half of the money should be spent on equipment. Turn key installations are not a good way to get the staff involved, although it may look like an efficient and fast way to get the network up. Slower progress with more involvement and learning are more desirable with sustainability in mind.The most common problem is to inadequately process the data implying little output from the network. It might be hard to get adequate software and training from companies since it is either too simple or too expensive. Fortunately public domain software, covering the needs of most networks, is available. Training may be best provided by well established scientific institutions that should aim to be objective and it should be done before any equipment arrives. Some companies also offer training using public domain software if asked to do so.It is suggested that in the planned guide, that organizations who have the experience, give courses in processing techniques (like e.g. the GFZ Unesco courses) and/or are willing to provide support (paid or unpaid) should be listed as well as references to well proven public domain software. As part of the planning document, examples of networks with indications of cost of instrumentation and training should be shown for different types and sizes of networks to give officials a realistic idea of costs. A reference can also be given to The New Manual of Seismological Observatory Practice, chapter 8, which deals with planning a seismic network from both a technical and organizational point of view.Examples from different countries will be given.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Kwiatek, Grzegorz
Schedule   Thu 3:30 PM / Oral
Room   Room 204/205
Scaling Relations of Source Parameters in Picoscale (-4.1<MW<-0.8): A Case Study from Mponeng Deep Gold Mine, South Africa
KWIATEK, G., GFZ German Research Centre for Geosciences, Potsdam, Germany, kwiatek@gfz-potsdam.de; PLENKERS, K., KIT Karlsruhe Institute of Technology, Karlsruhe, Germany, ; DRESEN, G., GFZ German Research Centre for Geosciences, Potsdam, Germany, ; JAGUARS research group
One of the major questions in seismology is whether the faulting mechanism of large and small earthquakes, as well as the fractures observed in laboratory experiments involves different physics [Prieto et al., 2004, JGR]. This may be of practical importance for understanding the nucleation and fracture process as well as for earthquake and rockburst hazard estimates. If we know the source parameters of seismic events resulted from analysis of laboratory fracture experiments or analysis of induced seismicity, we can easily extrapolate these values to those expected for larger, natural events.In this study we investigate the source parameters of pico- and nanoseismic events (MW>-4.0) recorded with a high-sensitivity seismic network at Mponeng gold mine, South Africa. Our aim is to link the laboratory experiments on rock samples to seismic events recorded in-situ and provide new insights into the ongoing discussion whether the self-similarity is preserved for extremely small seismic events. The JAGUARS network, composed of 3C accelerometer and 8 acoustic emission (AE) sensors is located at a depth of 3543m and covers the limited volume of approx. 300x300x300m. The AE sensors are effectively calibrated to the accelerometer in the frequency band 500Hz-17kHz. The waveform data of two datasets are analyzed: (1) aftershock sequence of a MW1.9 event that occurred 30m from our network and (2) post-blasting activity located at the exploitation level. Two different approaches are used: an absolute source inversion method and a spectral ratio method. The calculated values of MW ranged from -0.8 down to -4.1 with source sizes from 1.3m to 8cm. We do not observe a dependency of the static stress drop and apparent stress on seismic moment, but definitely a self-similar behavior of earthquake rupture process in the analyzed magnitude range. We find indications for slow rupture velocities and high stress offshoot of analyzed seismicity.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Froment, Bérénice
Schedule   Wed AM / Poster
Room   Ballroom B
Temporal Seismic Wave Speed Changes Associated With the May 12, 2008 Mw7.9 Wenchuan Earthquake
FROMENT, B., ISTerre, Université Joseph Fourier and CNRS, Grenoble, France, fromentb@obs.ujf-grenoble.fr; CHEN, J., Institute of Geology, China Earthquake Administration, Beijing, China, chenjh@ies.ac.cn; CAMPILLO, M., ISTerre, Université Joseph Fourier and CNRS, Grenoble, France, michel.campillo@obs.ujf-grenoble.fr; LIU, Q., Institute of Geology, China Earthquake Administration, Beijing, China, qyliu@ies.ac.cn
We used continuous recordings of ambient seismic noise in Sichuan, China to track the temporal evolution of the seismic wave speed at a regional scale, for 2 years including the great Wenchuan earthquake. The data were recorded by a temporary network of 156 broadband seismographs ran by the China Earthquake Administration, in a 200 km x 200 km region that covers the southern 2/3 of the fault system activated during the Wenchuan event. We computed cross correlation functions of continuous vertical records for all pairs of stations and we investigated temporal velocity changes with respect to a reference correlation. We carried out this analysis in different period bands. We first considered signals in the 1-3-s period band. We found clear evidence of a co-seismic velocity drop (up to 0.08% in the fault region after the Wenchuan earthquake while the velocity fluctuates within 0.02% in the months before the earthquake). We compared the measurements in different sub-arrays to get a spatial distribution of the velocity change. We observed that the co-seismic velocity drop is observable in a wide zone around the fault and that at regional scale, the velocity drop exhibits a better spatial correlation with the volumetric strain change during the Wenchuan earthquake than with the surface geology. In order to investigate deeper processes in the crust, we performed the same analysis on longer-period signals (around 20 s). The analysis in long-period bands requires more data to get satisfactory-quality measurements. We then used the whole correlation tensor deduced from 3-component noise records. We discuss observations obtained from this analysis and possible interpretations concerning deep crust behaviour in response to the Wenchuan earthquake. We also examined the quality and stability of the so-called C3 functions (i.e., Correlations of Coda of noise Correlations) to investigate the contribution of this iterative method on our velocity change measurements.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Shaw, Bruce
Schedule   Thu 4:30 PM / Oral
Room   Room 204/205
Surface Slip Gradients of Large Earthquakes
SHAW, B. E., Lamont Doherty Earth Observatory, Columbia University, Palisades, NY, shaw@ldeo.columbia.edu
For earthquakes which are large enough to break the Earth's surface,slip can be measured directly, providing model-independent informationof spatially varying behavior in earthquakes.Here new techniques are developed and applied to extractrobust measures of surface slip.In particular, I examine how differences in slip scale withdifferences in separation. Examining slip distributions of 7 largeearthquakes in a digital database I find collapse of the curves ontoa common behaviorover kilometer to tens of kilometer lengthscales.Distributions of differences of slip are found to be be reasonably wellfit by normal distributions, with thevariance of the distributions scaling with separation distance.In particular, average slip differences are seen to be increasing linearlyout to lengthscales of the seismogenic crust,but with a nonzero intercept when extrapolated back to zero separationof around 1m offset.The variability of slip extrapolated to zero separation,the mean offset, of around 1m(.96 +- .15 m)is a remarkable feature of the observations, holding forall 7 of the large earthquakes analyzed.Leaving aside the offset, and looking at the increaseas a function of separation, the slope or lateral strain has a valueconsistent with large scale average strains.Thus behavior consistent with constant stress dropis seenat lengthscales smaller than the eventsize, revealing a further invariant of earthquake dynamics.Finally, taking into account the noisy environment by lookingfor coherent structures unlikely to be noise related,I find structures which have moderate values oflateral strains, of order a factor of 10 times mean values,with values appearing to be independent oflengthscale and magnitude.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Oth, Adrien
Schedule   Wed 11:15 AM / Oral
Room   Room 204/205
Insights into the sources of variability of ground motion parameters from regression analysis of KiK-net data in Japan
OTH, A., European Center for Geodynamics and Seismology, Walferdange, Luxembourg, adrien.oth@ecgs.lu; BINDI, D., GFZ German Research Centre for Geosciences, Potsdam, Germany, bindi@gfz-potsdam.de
The inherent variability observed in earthquake strong ground motions constitutes a major challenge in engineering seismology, especially considering the design of critical infrastructure or when performing probabilistic seismic hazard assessment (PSHA), in particular using low exceedance probabilities.Considerable efforts are currently being devoted to the question of how the standard deviation (sigma) obtained during the derivation of ground motion prediction equations (GMPEs) could be reduced. For that purpose, it is necessary to consider the individual components of the variability (i.e. within-event and between-events variability) and gain insights into the factors controlling these. While the within-event residuals should be controlled by site response and potential lateral variations in path characteristics, the between-events variability should be to the largest extent caused by earthquake source effects.We investigate the sources of these components of variability using the extraordinary extensive dataset of accelerometric recordings obtained at the KiK-net network in Japan during the last decade. We perform regressions for GMPEs using both borehole and surface data and derive the within-event and between-events components of variability for spectral accelerations ranging between 0.01 to 2 s. Taking advantage of the results of a previous large-scale generalized spectral inversion of K-NET and KiK-net data, we analyze these variability components and their correlation to parameters such as earthquake stress drop, peak resonance frequency of site response functions or vS30. Our results provide hints on which effects are the most relevant in causing ground motion variability and what strategy could be most promising in order to reduce sigma.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Oth, Adrien
Schedule   Thu 2:30 PM / Oral
Room   Room 204/205
A critical comparison of the source scaling characteristics of individual aftershock sequences in Japan versus nation-wide seismicity
OTH, A., European Center for Geodynamics and Seismology, Walferdange, Luxembourg, adrien.oth@ecgs.lu
The question whether earthquake source parameters scale self-similarly or not is still a matter of partially vigorous debate. One major difficulty in this discussion is related to the most basic step of it, i.e., the reliable determination of earthquake source parameters in the first place. Traditional approaches are often hampered by insufficient knowledge on path and site effects, which the recorded ground motions need to be corrected for in order to derive the source characteristics, and in many cases, the available datasets are too scarce for allowing the reliable resolution of the trade-offs between the different effects. To avoid these problems, Empirical Green’s Functions (EGF) approaches are a commonly used alternative, which however restricts the useable events to approximately co-located large and small earthquakes with similar source mechanisms. As a result, the vast majority of source scaling studies are performed on individual mainshock/aftershock sequences, which provide ideal conditions for the application of the EGF techniques. Significant breaks in self-similarity are most commonly seen in such studies based on individual sequences, and whether these represent a more general behavior, i.e., also apply to small and large events not necessarily belonging to the same sequence, remains an unclear issue.In this study, I use the extensive datasets recorded by the K-NET and KiK-net networks in Japan during recent years, allowing for a nation-wide robust estimation of source, path and site characteristics by means of generalized spectral inversion. The results provide clear indications that over the entirety of Japan, self-similarity seems to hold over the magnitude range 3-8. In order to decipher whether or not this holds also true for individual earthquake sequences, I extract several major sequences from this dataset and investigate how their scaling behavior compares in-between each other and to the entirety of the Japanese archipelago.
Session:Combining Geodetic and Seismic Measurements
Presenter   McIntyre, Jonathan
Schedule   Fri PM / Poster
Room   Ballroom B
Instrumentation and Installation of the Central United States Seismic Observatory (CUSSO)
MCINTYRE, J. L., Kentucky Geological Survey, Lexington, KY, Jonathan.McIntyre@uky.edu; WANG, Z., Kentucky Geological Survey, Lexington, KY, zmwang@uky.edu; WOOLERY, E. W., University of Kentucky - Dept. of Earth & Environmental Sciences, Lexington, KY, woolery@uky.edu; STEINER, G., VLF Designs, Inc., Jackson, MO, vlf@cablerocket.com
A combination of tiltmeters, strong-motion accelerometers, and medium-period (0.06–50 Hz) seismometers are currently installed at varying depths within the 594-m borehole comprising part of the Central U.S. Seismic Observatory (CUSSO) in Fulton County, Kentucky, near the center of the New Madrid Seismic Zone. This borehole penetrated through 586 m of loose to stiff unconsolidated sediments and was terminated 8 m into Ordovician bedrock. Electrical (resistivity, SP, gamma), sonic velocity (P- and S-wave), and borehole deviation surveys were conducted prior to the instrumentation installation. In addition, a detailed lithologic log and other site characterizations were completed at the site. CUSSO also has two other instrumented boreholes (30-m and 244-m) and surface instrumentation. The surface instrumentation consists of a vault containing a medium-period seismometer and a strong-motion accelerometer. The 30-m and 244-m seismic boreholes each contain strong-motion accelerometers.CUSSO is unique in providing the ability to record and analyze earthquake ground motions from within the bedrock, within the unconsolidated sediments, and free-field ground motions at a site with soil/sediment deposits thicker than 100 m. CUSSO also provides a tool for evaluation of current analytical models for deep soil sites. Several analytical models are currently being used to predict the seismic response of deep soil sites; however, these analytical procedures have not been validated for sites deeper than 100 m. CUSSO, in combination with other instrumentation of the Kentucky Seismic and Strong-Motion Network (KSSMN), as well as other networks in the region, will provide a better constraint on seismic hazard and risk assessments in the central United States.This presentation will detail the installation of seismic instrumentation, including the types of instrumentation used as well as some of the challenges encountered.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Mazzotti, Stephane
Schedule   Thu 4:00 PM / Oral
Room   Ballroom C
Comparison of GPS and Seismicity Deformations Rates in Eastern Canada
MAZZOTTI, S., Geological Survey of Canada, Natural Resources Canada, Sidney, BC, Canada, smazzotti@nrcan.gc.ca; HENTON, J., Geodetic Survey Division, Natural Resources Canada, Sidney, BC, Canada, jhenton@nrcan.gc.ca; CRAYMER, M., Geodetic Survey Division, Natural Resources Canada, Ottawa, ON, Canada, mcraymer@nrcan.gc.ca
We present an update of the present-day velocity and strain rate fields in Eastern Canada using a combination of ~100 continuous and campaign GPS stations, with time spans of 5 – 15 years and spatial densities of 20 – 200 km. As shown previously, the primary source of crustal deformation is ongoing postglacial rebound, although second-order deformation rates of < 1 mm/yr may relate to local concentrations of earthquakes. In order to test the resolvability of sub mm/yr deformation signals related to seismicity, we process the GPS data with the most recent IGS products (repro1) and using both Precise Point Positioning and double-difference approaches, which allows us to test the resolution of each approach. We also investigate the precision of velocities and strain rates derived using continuous vs. campaign and short-baseline vs. long-baseline data. We present a preliminary solution for a high-density campaign GPS network deployed along the St. Lawrence Valley and spanning areas of high seismicity (Charlevoix) and low seismicity (Trois Rivieres). A comparison of GPS versus seismicity deformation rates, with a detailed analysis of uncertainties in both datasets, allows us to check if the spatial variations in the seismic activity can be related to similar variations in GPS strain rates - and thus potential strain loading along seismogenic faults of the St. Lawrence Valley.
Session:Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Presenter   Mazzotti, Stephane
Schedule   Thu 2:30 PM / Oral
Room   Ballroom C
Impact of episodic earthquake clusters on seismic hazard assessment in continental intraplate regions
MAZZOTTI, S., Geological Survey of Canada, Natural Resources Canada, Sidney, BC, Canada, smazzotti@nrcan.gc.ca; HALCHUK, S., Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, Canada, Stephen.Halchuk@NRCan-RNCan.gc.ca; ADAMS, J., Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, Canada, John.Adams@NRCan-RNCan.gc.ca
One of the main limitations of probabilistic seismic hazard analysis (PSHA) in continental intraplate regions is the long return period of large, damaging earthquakes (100s – 1000s yr), compared to the short sample of instrumental and historical earthquake data (10s – 100s yr). As a result, earthquake catalogs may not provide a robust representation of the locations and frequencies of future large earthquakes, leading to inaccurate seismic hazard assessments. As suggested in recent studies, this effect may be exacerbated by the possibility that episodic clusters of earthquakes may represent aftershock sequences that last for 100s yr, the mainshocks of which occur along geological structures on time scales of 1000s yr. Cluster migration might thus be actual (due to stress transfer at the ends of a cluster) or apparent (due to random occurrence of the mainshocks), but we can hypothesize that, in time, the clusters accommodate a uniform amount of deformation along the geological structures. We present a statistical analysis of the impact of such potential cluster migrations and aftershock sequences on PSHA using synthetic earthquake catalogs. The magnitude-frequency distributions of background and clustered seismicity are tuned to match the earthquake catalog, seismic moment rate, and deformation rate estimated for eastern Canada’s St. Lawrence Valley system. The simple statistical approach allows us to test the sensitivity of PSHA at various exceedance periods for a range of seismicity cluster sizes, migration rates, and aftershock decay rates. These results may provide a basis for a new set of models in the future Canadian seismic hazard maps.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Cramer, Chris
Schedule   Thu 9:15 AM / Oral
Room   Room 204/205
Memphis, Tennessee, Urban Hazard Mapping: Future Directions
CRAMER, C. H., CERI, University of Memphis, Memphis, TN, ccramer@memphis.edu; VAN ARSDALE, R. B., Dept. Earth Sciences, Univ. of Memphis, Memphis, TN, rvanrsdl@memphis.edu
In 2004, Memphis urban seismic hazard maps were completed for a six-quadrangle area centered on Memphis and southern Shelby County. Both probabilistic and scenario seismic and liquefaction hazard maps were generated for the six quadrangle study area. These urban seismic hazard maps have been well received, particularly the liquefaction hazard maps, and used by consultants and public agencies to address seismic hazard mitigation in the Memphis area. Since then, Stevens (2007) updated and expanded the upper 100 m of the 3D geologic model to all of Shelby Co. and Csontos (2008) has improved the 3D geologic model for the Mississippi embayment sediments, including under Memphis and Shelby Co. Included in the geologic model is improved modeling of sharp geologic changes due to faults and/or erosion of strata. Additionally, the USGS national seismic hazard model has been updated in 2008 (Petersen et al., 2008). The Memphis urban seismic hazard mapping can be expanded to all of Shelby Co (six more quadrangles plus two partial quadrangles) and updated with increased resolution and the 2008 USGS hazard model, including attenuation relations.Likely, guidelines will be needed in the future to selecting possible CEUS urban seismic hazard mapping projects. These guidelines should be based on population and infrastructure at risk, community support, and willingness of professional participation. FEMA 366 on estimated annualized earthquake losses in the US can help prioritize communities at risk of earthquake loss. Community interest can be measured by the presence of support by local government, societies, and business, such as happened in Evansville, IN. Willingness of professional participation can be gauged by the formation of a technical working group to guide and disseminate hazard maps, such as in St. Louis, MO-IL.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Hosseini, S.Mehrdad
Schedule   Wed 4:15 PM / Oral
Room   Ballroom D
Identification and Inversion of Rayleigh Wave Dispersion Using a Multi-Mode Approach
HOSSEINI, M., The University of Memphis, Memphis, TN, shsseini@memphis.edu; PEZESHK, S., The University of Memphis, Memphis, TN, spezeshk@memphis.edu
One of the non-invasive methods to investigate properties of shallow soil profile is the multichannel analysis of surface waves (MASW) method. Using data recorded on a straight series of sensors array, it is possible to determine the shear wave velocity and thickness of soil layers using a harmonic source with ability of multi-frequency excitation. Result of field test, is the phase velocity of Rayleigh waves in frequency domain (dispersion curve). The process of inversion is to determine a soil profile with appropriate number of layers and their corresponding shear-wave velocities, which results in a theoretical dispersion curve that matches the experimental dispersion curve. Due to the nature of inversion problem, there is no unique profile; therefore, different soil profiles are selected and fed into the propagation equation of Rayleigh waves and by comparison of theoretical dispersion curves and the experimental one, the best profile can be selected using the least square method as the final solution of inversion. Considering the complexity and plurality of parameters, in this study genetic algorithm was selected as the engine to produce different soil profiles. Best features of the genetic algorithm are avoiding being trapped in local optimal solutions and also avoiding dealing with gradients. Furthermore, by considering higher modes, the number of soil profiles as possible solutions is reduced. Main effect of such an implementation is more robust solution in comparison with solution determined by inversion of problem using the fundamental mode. To account for poor signal to noise ratio, the refraction Micrometer (ReMi) method was also used to have more solid composite dispersion curve. Results of such composite application of MASW and ReMi method is compared with down-hole test results, and it is observed that with an acceptable range of standard deviation, the results of this investigation addresses the real field condition.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Porritt, Robert
Schedule   Thu 9:30 AM / Oral
Room   Ballroom D
Segmentation of Lithospheric Structure in the Cascadia Subduction Zone
PORRITT, R. W., UC Berkeley, Berkeley, CA, rob@seismo.berkeley.edu; ALLEN, R. M., UC Berkeley, Berkeley, CA, rallen@berkeley.edu; BOYARKO, D. C., Miami University of Ohio, Oxford, OH, ; BRUDZINSKI, M. R., Miami University of Ohio, Oxford, OH, ; O'DRISCOLL, L., Oregon University, Eugene, OR, ; ZHAI, Y., Rice University, Houston, TX, ; LEVANDER, A. R., Rice University, Houston, TX, ; POLLITZ, F. F., USGS, Menlo Park, CA,
Along strike variation has been observed throughout the Cascadia Subduction Zone in multiple studies with complementary data sets. Body-wave tomography shows a broad zone in the center of the slab with a weak high velocity signal in an atypically quiescent seismic zone (Obrebski and Allen, 2009). Characteristics of primitive basalts found in the arc volcanoes change along strike defining four distinct magma sources or plumbing systems (Schmidt et al, 2007). However, the most striking variation is in the recurrence rate of episodic tremor and slip throughout the region (Brudzinski and Allen, 2007). Determining the detailed velocity structure of the lithosphere will help to unravel what role it plays in controlling the along strike variation of these separate observations.This study improves on previous observations by analysis of a shear wave velocity model from ambient seismic noise cross-correlations with two Flexible Array deployments in addition to regional networks and the Transportable Array. Longer period bands than typically observed in ANT are recovered via improved statistical analysis resulting in robust group and phase velocity maps from 7-92 seconds. Thus structure is well resolved from the surface to approximately 100km in depth allowing for simultaneous interpretation of crust and uppermost mantle structure. By analysis of the three dimensional structure of the subduction zone key observations regarding the above segmentation are made. The three zones of distinct tremor recurrence are marked by variable structure in the overriding continental crust and near the plate interface. The along strike variation of the main arc volcanic signature is evident as the southern region is dominated by large low velocity zones where the northern region has more discrete low velocity zones. We attribute this variable structure as the effects of variable accretion in the wake of the Farallon slab as the Gorda and Juan de Fuca plates continue subduction.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Cramer, Chris
Schedule   Wed 9:45 AM / Oral
Room   Ballroom C
Comparison of 1811-1812 New Madrid and 1929 M7.2 Grand Banks Earthquake Intensity Observations: Why the New Madrid Earthquakes Are M7-8 Events
CRAMER, C. H., CERI, University of Memphis, Memphis, TN, ccramer@memphis.edu; BOYD, O. S., U.S. Geological Survey, Memphis, TN, olboyd@usgs.gov
The 1811-1812 New Madrid earthquake intensity observations and assigned magnitudes have been subject to downward revision in the last decade. The most recent intensity revision (2010) lowers intensity assignments for modified Mercalli intensity (MMI) VI and above, resulting in estimated magnitudes as low as M6 for the largest events. As suggested by Evernden (1975), the near-in, higher intensity values are influenced by magnitude, source depth, and focal mechanism, while the further away lower intensity values are influenced mostly by the magnitude of the earthquake. So lowering near-in intensities but not further-away values does not necessarily imply a lowering of assigned magnitude. We check this by fitting intensity observations for each of the four largest New Madrid 1811-1812 earthquakes and for the 1929 Grand Banks earthquake using the form ln(MMI) = A + C*dist + D*ln(dist). Comparing the median curve and its 95% confidence interval for each New Madrid event with that of the 1929 M7.2 Grand Banks earthquake, the December 16, 1811 and the February 7, 1812 mainshocks have significantly higher median intensity curves and therefore likely higher magnitudes than the Grand Banks event. The January 23, 1812 mainshock likely has a similar magnitude and the largest aftershock of the sequence, which occurred on December 16, 1811, likely has a smaller magnitude than the Grand Banks event. This pattern is true for both the new and previous (2000/2002) New Madrid intensity assignments, indicating that lowering near-in intensities without lowering further out intensities has little effect on the magnitude assignment. We also used the Wald and Atkinson (2007) intensity attenuation relation for the central and eastern US and found the magnitude corresponding to the minimum difference in the median fit to the new 1811-1812 New Madrid intensity values. These best-fit magnitudes suggest low to upper M7s for these four New Madrid events.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Moran, Kent
Schedule   Wed 9:30 AM / Oral
Room   Ballroom C
New Uses for Old News: Historic Methodology and the Discovery and Revision of New Madrid Intensity Reports
MORAN, N. K., University of Memphis/CERI, Memphis,TN, nkmoran@memphis.edu
The New Madrid earthquakes of 1811-1812 generated much interest in the contemporary newspapers that existed in the United States and led to the recording of information that can be of value for the assessing of both magnitude and site effects. With the passage of time these accounts had become obscured and forgotten as the newspapers they were recorded in were archived and forgotten. With first the advent of preservation efforts for these newspapers and then the invention of modern methods of accessibility, these accounts can be utilized to develop a more complete record of the earthquakes. Historic research methods in combination with modern technology can help seismologists to gain a deeper understanding of these historic earthquakes. For example catalogs of felt reports for the earthquakes have evolved as more information becomes accessible. Each successive effort has been limited by the sources available to it. More modern search and archival technology has meant that previously unknown accounts can be found and more information can be discovered on existing accounts to check them for accuracy and completeness. The use of historic sources such as newspaper articles, personal journals, and historic reports can help to further define felt areas and the magnitude of the earthquakes. However their use has to be done with an abundance of caution with the emphasis for finding the earliest and most accurate version of an account to ensure data quality. The use of historic sources recorded long after a historic event must be done with caution. A careful review and updating of 1811-1812 earthquake observations with new material discovered since Street and Nuttli (1984) is shedding new light on the intensities and magnitudes of these events. A web-accessible, enhanced collection of original source material for these events is now available at the Center for Earthquake Research and Information at the University of Memphis.
Session:Joyner Lecture
Presenter   Hanks, Thomas
Schedule   Thu 6:15 PM / Oral
Room   Ballroom C
Joyner Lecture: Extreme Ground Motions
HANKS, T. C., USGS, Menlo Park, CA, thanks@usgs.gov
Extreme Ground Motions are the extremely large amplitudes of earthquake ground motions that arise at extremely low probabilities of exceedance (hazard levels). They were born in the extension of the 1998 probabilistic seismic hazard analysis (PSHA) for Yucca Mountain (Stepp et al., 2001) to a hazard level of 1E-8/yr (1E-4 for a 10,000-year repository lifetime). This gave rise to peak ground accelerations (PGA) ≥ 11g and peak ground velocities (PGV) ≥ 13 m/sec, ground-motion values that caused considerable consternation in many sectors of earthquake-science and earthquake-engineering circles. In 2005, the U.S. Department of Energy launched a five-year research program (ExGM) to investigate the origin, nature, and plausibility of extreme ground motions. This presentation will be a very brief summary of what we have learned in the course of ExGM, in which several dozen scientists and engineers participated.The three basic themes of ExGM research are physical limits to ground motion in bedrock, unexceeded ground motions, and frequency of occurrence of various ground-motion measures (such as PGA and PGV) or things that control them (such as earthquake stress drops or faulting displacements). Physical limits define ground motions that cannot occur, ever. Unexceeded ground motions are ground motions that have not yet occurred, as presented by fragile geologic structures of known lifetime, but may occur at any time. Fragile geologic structures are the only way to validate (or invalidate) PSHA calculations over long periods of time. Frequency-of-occurrence research focused on various distribution functions, which control the aleatory uncertainty in PSHA that is especially important at low hazard levels.The specific application of the methods, models, and data we developed in the course of ExGM is to seismic hazards for Yucca Mountain; we find that the 1998 mean seismic hazard curve significantly overstates the seismic hazard we infer from the findings of ExGM research. The methods and models developed in the course of ExGM are quite general, however, and may be applied to critical facilities anywhere in the world; they will be especially valuable at the low hazard levels that ExGM confronted.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   JAISWAL, KISHOR
Schedule   Fri AM / Poster
Room   Ballroom B
Virtual Representation of Earthquake Shaking, Population Exposure and Loss Information
JAISWAL, K. S., U.S. Geological Survey (contracted through- Synergetics Inc.), Golden, CO, KJAISWAL@USGS.GOV; WALD, D. J., U.S. Geological Survey, Golden, CO, ; MATHIAS, S., U.S. Geological Survey, Golden, CO,
The Prompt Assessment of Global Earthquakes for Response (PAGER) system provides an estimate of population affected at different levels of shaking intensity after significant earthquakes worldwide. Such estimates are typically portrayed with 2-D graphical images that show the extent of shaking intensity and the distribution of the affected population. Zooming in and identifying the most-affected regions is not possible using such static maps. Here, the interactive visual capability of Google Earth is combined with the shaking hazard estimates of USGS ShakeMap, and population exposure estimates available through the LandScan database to produce a new PAGER product. Both shaking intensity estimates and population counts are resampled at uniform resolution (i.e., approximately 1-sq km cell size). These files, made available in KMZ format, when viewed in Google Earth portray 3D geo-referenced color-coded bar plots with heights scaled to the grid-level population and colors corresponding to shaking intensity using the ShakeMap color palette. The bar plot allows users to select the level of shaking intensity of interest and then visualize the population that is affected at that shaking level. In addition, this visualization strategy allows the user to select an appropriate transparency level so that all three elements may be seen simultaneously (i.e., population, shaking intensities, and Google Earth’s underlying remotely-sensed imagery showing buildings and infrastructure). Since it is derived from the same source of information that PAGER produces but with the added visual and interactive capability, this product directly compliments the overall PAGER objectives and helps its user-base in the post-earthquake response environment. While it is also possible to portray the spatial distribution of PAGER’s casualty and damage/loss estimates in this way, uncertainties in the loss model demand that such representation only be used for developers exploring model results.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Gomberg, Joan
Schedule   Thu 4:00 PM / Oral
Room   Room 204/205
Earthquake Scaling Inferences from Observations of Coupled Seismic and Aseismic Slip
GOMBERG, J., US Geological Survey, Seattle, WA, gomberg@usgs.gov; PREJEAN, S., US Geological Survey, Anchorage, AK, sprejean@usgs.gov; PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng.seismo@gmail.com; RUPPERT, N., University of Alaska Fairbanks, Fairbanks, AK, natasha@gi.alaska.edu
Recent growth of observations has led to new appreciation of the variety of ways in which faults slip. In particular, measurements of coupled aseismic and seismic slip, including new seismic signals, have provided new windows into the faulting process. Models explaining this variety commonly feature faults with heterogeneous strength and frictional properties that govern rupture evolution. We summarize two studies of coupled seismic and aseismic deformation and their implications for earthquake scaling.One interpretation of moment and duration estimates for numerous slip events classifies sources as either ‘fast’ or ‘slow’, in which moment is proportional to duration cubed or duration, respectively [Ide et al., 2007]. While this interpretation implies a new class of ‘slow’ slip events with distinctly different rupture processes from traditional earthquakes, we suggest alternative interpretations are possible. We compiled a larger suite of moment and duration estimates and suggest it is consistent with observational limitations rather than source differences, and indicates a continuum of slip modes exits between the inferred ‘fast’ and ‘slow’ trends. Our second study focuses on hypotheses that tremor accompany mainshock afterslip and may reveal precursory slip. We tested these using seismic data before and after the M7.9 Denali fault, Alaska earthquake. Although challenged by abundant aftershock signals, we conclude no significant tremor activity occurred. We propose a model that explains this result as well as published analyses of geodetic, geologic, and seismic co- and post-seismic deformation. Our model invokes a distribution of frictional properties akin to those attributed to subduction zones that exhibit aseismic slip and tremor within a transition zone, and a mainshock that ruptures through this zone. This model is consistent with theories that predict only sufficiently large earthquakes may drive rupture outside the frictionally locked zone.
Session:Earth Structure Observations and Theory
Presenter   Skobeltsyn, Gleb
Schedule   Thu 11:30 AM / Oral
Room   Ballroom E
Uppermost Mantle S-wave Velocity Structure of the East Anatolian-Caucasus Region
SKOBELTSYN, G. A., Department of Geological Sciences, University of Missouri, Columbia, MO, gs5ff@mail.missouri.edu; MELLORS, R., Lawrence Livermore National Laboratory, Livermore, CA, mellors1@llnl.gov; GOK, R., Lawrence Livermore National Laboratory, Livermore, CA, gok1@mail.llnl.gov; TURKELLI, N., Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey, turkelli@boun.edu.tr; SANDVOL, E., Department of Geological Sciences, University of Missouri, Columbia, MO, sandvole@missouri.edu
The East Anatolian-Caucasus region is a part of the orogenic belt which formed as the result of the closure of the Neo Tethys Ocean and the corresponding continental collision of Arabian and Eurasian plates. Our study includes the southwestern part of the Caspian basin, the Kura basin, the Lesser and Greater Caucasus mountains, and the East Anatolian plateau. In order to develop a 3D S-wave velocity model of the regional uppermost mantle we collected data which was recorded by 26 permanent broadband stations located in eastern Turkey and Azerbaijan during January of 2006 – July of 2008. In addition, we used the data from the ETSE network (1999-2001). We selected total of 63 teleseismic events with surface wave magnitudes larger than 5.8 and with good signal to noise in the longer periods. We used the method of Yang and Forsyth (2006) to determine the fundamental mode Rayleigh wave phase velocities at 13 periods between 20 and 143 seconds. The phase velocity maps show a broad low velocity zone beneath eastern Anatolia and two relatively high velocity zones located under the eastern part of the Greater Caucasus and the Talesh. Furthermore the regional uppermost mantle appears to be relatively isotropic. We inverted the Rayleigh wave phase velocities using the algorithm of Saito (1988) to obtain the 3D S-wave velocity model (0-250 km). The low velocity zone is observed starting right at the Moho down to 150 km, which suggests asthenospheric material underlying a very thin lithosphere. The high velocity body beneath the eastern Greater Caucasus lies at depths below the Moho down to 180 km, and apparently is either a subducting slab or a thick lithospheric mantle root. The high velocity body beneath the Talesh is observed below 160 km. We believe this high velocity body represents a remnant Neo Tethys slab that broke off after the initiation of continental collision between Arabia and Eurasia.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   McWhirter, Leslie
Schedule   Wed PM / Poster
Room   Ballroom B
New Strategies for Developing Vs30 Maps
MCWHIRTER, L., U.S. Geological Survey and Colorado School of Mines, Golden, CO, lgodfrey@usgs.gov; WALD, D. J., U.S. Geological Survey, Golden, CO, wald@usgs.gov; THOMPSON, E. M., Tufts University, Medford, MA, eric.thompson@tufts.edu
A limiting aspect of existing state-of-the-art strategies for generating estimated Vs30 maps from geologic (e.g., Wills and others) and topographic base maps (e.g., Wald and others) is that, while initially derived from and constrained by observed Vs30 values, both approaches fail to incorporate the original Vs30 measurements back into the map that has been created. Furthermore, while both predictive methods bring unique benefits to the problem, they are rarely used in combination with each other and with the Vs30 measurements. Because many seismic-hazard mapping studies and ground-motion prediction equations fundamentally rely on Vs30 as the site response explanatory variable, these problems require further attention. In this study, we examine alternative strategies to map Vs30 with estimated and observed Vs30 combinations, recognizing that the weighting at any location should be made with consideration of the spatial uncertainties of each of the contributing inputs. We examine kriging-with-a-trend and cokriging methodologies against gridded processing strategies that allow more customization of the interpolation. The latter approach is analogous to ShakeMap’s strategy of allowing a fundamentally predictive map to be both modified locally by ground-shaking data as well as by biasing the overall estimation equations in favor of the data. In the process of developing an optimal strategy for Vs30 map development, we are exploring: 1) the incorporation of measured Vs30 back into the map, 2) the use of higher-resolution (9 rather than 30 arc-second) topography, 3) the employment of on-the-fly slope-based Vs30 correlations to better fit regional trends of Vs30 datasets, and 4) the addition of many Vs30 data not available in earlier studies. Ideal candidates for calibrating this methodology include Taiwan; Salt Lake City, Utah; and California.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Marrone, James
Schedule   Fri AM / Poster
Room   Ballroom B
In Search of a Broadly Applicable Enveloping Design Response Spectrum for Critical Nuclear Facilities
MARRONE, J. E., Bechtel Corporation, San Francisco, CA, jmarrone@bechtel.com; MCLANE, T., Bechtel Power Corporation, Frederick, MD, tjmclane@bechtel.com; MCHOOD, M., Bechtel Power Corporation, Frederick, MD, mxmchood@bechtel.com; LITEHISER, J. J., Bechtel Corporation, San Francisco, CA, jjlitehi@bechtel.com
There is renewed interest in increasing nuclear power plants [NPPs] electricity-generating capacity in the US. Under Federal law (10 CFR 100.23) site-specific earthquake design ground motions must be determined for any new NPP. This has led to the evaluation of site-specific design response spectra at several central and eastern US [CEUS] locations. These site-specific motions – e.g., the Ground Motion Response Spectrum [GMRS], as defined in Reg. Guide 1.208 – form the basis for comparison with the Certified Seismic Design Response Spectra [CSDRS] for which certain structures, systems, and components (SSCs) of the nuclear facility are qualified on a generic basis. To avoid supplemental structural analysis of SSCs, the goal of the applicant for a license to construct and operate the new NPP is to show that site-specific design motions are enveloped by the CSDRS at all spectral frequencies. As addressed in several Final Safety Analysis Reports docketed with the NRC, site-specific motions have not always been enveloped by a given CSDRS, especially for frequencies greater than 10 Hz. In this context we examine readily available regional ground motions to help develop a CSDRS that would envelop most regional site-specific motions. While FSARs consider updated EPRI (1989) seismic models to develop design ground motions at a few sites, the 2008 USGS National Hazard Map [NHM] results, from which rock GMRS may be calculated, are broadly available. Results indicate interesting differences in relative seismic hazard between the Western US and CEUS at the 10,000 and 100,000 year return periods required for NPP design. Comparisons are made between the NHM-based and FSAR-based rock GMRS for several CEUS sites. While the scatter is high, the NHM-based GMRS trend fairly consistently with the FSAR results for high frequencies, but trend higher than the FSAR results for low frequencies.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Guo, Lianghui
Schedule   Thu AM / Poster
Room   Ballroom B
Regional Geophysical Setting of the Reelfoot Rift and New Madrid Seismic Zone
GUO, L., China University of Geosciences (Beijing), Beijing, China, guo_lianghui@163.com; KELLER, G. R., University of Oklahoma, Norman, OK, grkeller@ou.edu
The reactivation of faults associated with the Reelfoot rift has long been considered to be the factor that has localized the seismicity in the New Madrid Seismic Zone. The Reelfoot rift is an intracratonic graben system, which formed in the Early Cambrian as a result of breakup of the Rodinian supercontinent. It strikes northeastward into the continent, and is approximately perpendicular to the rifted margin of the Laurentia that is shaped by the southeast-striking Alabama-Oklahoma transform fault. The northern section of the rift connects at least to some degree with other extensional structures in western Kentucky and southern Illinois. However, the southern end of the rift is obscure, and the relationship between the Reelfoot rift and the rifted margin of Laurentia remains disputed. We analyzed data from the national gravity and magnetic databases for the U. S. for a large area centered on the Reelfoot rift region. We used a variety of new data enhancement techniques to shed some light on regional structural relationships. Complete Bouguer gravity data and total magnetic intensity (TMI) data were assembled and gridded; the TMI data were then reduced to the magnetic pole. Then the data were processed to attenuate the high-frequency noise, and we analyzed the regional and residual anomalies. Specifically, we calculated the tilt derivatives of the data grids. We then calculated the directional horizontal derivatives of the tilt-angle derivatives both along and perpendicular to the strike of the rift. The maps of these derivatives clearly delineate the boundaries of the edges of the Reelfoot rift, the leading edge of the Ouachita thrust belt and the margin of Laurentia. The results of our analysis indicate that the southern end of the rift connects to the edge of the Cambrian continental margin that is marked by gravity and magnetic maxima probably related to mafic intrusions due the final phase of the break-up of Rodinia in the Cambrian.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Michael, Andrew
Schedule   Fri 1:45 PM / Oral
Room   Ballroom E
Testing the Agnew and Jones Foreshock Probability Method with Aftershocks
MICHAEL, A. J., USGS, Menlo Park, CA, michael@usgs.gov
The method of Agnew and Jones (JGR, 1991) estimates the probability that an observed earthquake will be a foreshock to a larger one by artificially separating earthquakes into aftershocks (which are discarded), mainshocks (events to be forecast), foreshocks (which are always followed by mainshocks), and background events (the remaining events). If the rates of events in the latter three classes are known, then their method estimates the probability that a candidate event, which may be either a foreshock or a background event, is a foreshock. In this method, as implemented with a fixed probability of foreshocks before mainshocks, the probability that a candidate event is a foreshock is approximately inversely proportional to the rate of background events. Thus, in areas of high seismicity rate the odds that any particular earthquake will be a foreshock are lower than the odds in regions with lower seismicity rates. If there is no physical difference to support the artificial separation of foreshocks and other earthquakes then this model implies that the ability of earthquakes to trigger other events is inversely proportional to the seismicity rate. I test the validity of this implication by separating the southern California seismicity into clusters, dividing the clusters into three groups based on the seismicity rate estimated with a 10 or 50 km Gaussian smoothing kernel, and then determining the mean abundance of aftershocks for each group using the method of Christophersen and Smith (BSSA, 2008). Depending on the choice of clustering and rate determination parameters, the results show that the triggering potential of earthquakes is either constant with respect to seismicity rate or is slightly greater in areas of higher seismicity rate (although those differences may not be statistically significant). There are no cases that show the pattern predicted by the Agnew and Jones construct and therefore it might not be applicable to real earthquakes.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Stewart, Jonathan
Schedule   Wed 10:30 AM / Oral
Room   Ballroom E
Engineering perspective on validation and calibration of physics-based ground motion simulations
STEWART, J. P., UCLA, Los Angeles, CA, jstewart@seas.ucla.edu; SEYHAN, E., UCLA, Los Angeles, CA, eseyhan@ucla.edu; GRAVES, R. W., USGS, Pasadena, CA, rwgraves@usgs.gov
Broadband ground motion simulation procedures typically utilize physics-based modeling of source and path effects at low frequencies coupled with semi-stochastic procedures at high frequencies. Prior to consideration for engineering application, simulation results should be verified by comparing outcomes (at low frequencies) from independent computational platforms for a common set of source and path conditions. Following verification, there is a need for validation and calibration of simulation results relative to ground motion data or data-driven ground motion prediction equations (GMPEs). The lack of engineering application of broadband simulations in the western U.S. to date reflects, in part, validation and calibration that has not adequately convinced engineers of the reliability of simulation tools. In general, the following procedures have been used for validation/calibration: (1) Waveform comparisons using earthquake data; (2) Ground motion intensity measures (IM) comparisons using earthquake data; (3) Ground motion IM comparisons using GMPEs. These procedures validate simulations in the sense that computed motions (or their IMs) are checked against data or GMPEs. Relative attributes of these techniques will be described. Relatively formal calibration involves adjusting model parameters to achieve specified attributes in simulated motions. An calibration process for high-frequency components of the Graves-Pitarka broadband simulation procedure is described. The result of this calibration exercise is simulated ground motions for southern California earthquakes that are considered suitable for preliminary engineering application.
Session:Verification Science
Presenter   Zhao, Lian-Feng
Schedule   Fri 4:45 PM / Oral
Room   Room 204/205
Regional Seismic Characteristics of Two North Korean Nuclear Tests
ZHAO, L. F., Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, zhaolf@mail.igcas.ac.cn; XIE, X. B., Institute of Geophysics and Planetary Physics, UCSC, Santa Cruz, CA, xxie@ucsc.edu; WANG, W. M., Institute of Tibetan Plateau Research, Chinese Academy Sciences, Beijing, China, wangwm@itpcas.ac.cn; YAO, Z. X., Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, yaozx@mail.igcas.ac.cn
Nine vertical-component regional seismograms from the 25 May 2009 North Korean nuclear explosion are recorded on a regional seismic network located in Northeast China and Korean Peninsula. For these stations, eight of them also recorded the 9 October 2006 North Korean nuclear test. Comparing the waveforms and the spectral features from these two events, the energy for the 25 May 2009 event is found to be approximately 5 times of the earlier one. Additionally, 599 vertical broadband seismograms from a group of regional earthquakes and chemical explosions are recorded by the same network and used to calibrate the network magnitude for Lg and Rg-waves. Then, the Lg and Rg magnitudes are calculated as mb(Lg) = 4.53 and Ms(Rg) = 3.71 for the 25 May 2009 event, and mb(Lg) = 3.93 and Ms(Rg) = 2.94 for the 9 October 2006 event. The regionally averaged Pn-velocity obtained based upon 15 first arrivals from these two events is between 7.95 and 7.99 km/s. This velocity supports that the modified fully coupled magnitude-yield relation is appropriate for the North Korean nuclear test site. The yield of the 25 May 2009 North Korean nuclear test is estimated to be 2.33 kt under the minimum source buried-depth assumption. The P/S-type spectral ratios for Pg/Lg, Pn/Lg, and Pn/Sn are calculated for the nuclear explosions and a group of earthquakes close to the test site. At frequencies above 2 Hz, the network-averaged P/S spectral ratios clearly separate the two explosions from the regional earthquakes.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Frary, Roxanna
Schedule   Wed PM / Poster
Room   Ballroom B
3D Controls on Basin Structure from a Network of High-Resolution Seismic Imaging Profiles in South Reno, Nevada
FRARY, R. N., University of Nevada, Reno, NV, rfrary0615@gmail.com; LOUIE, J. N., University of Nevada, Reno, NV, louie@unr.edu; STEPHENSON, W. J., US Geological Survey, Golden, CO, wstephens@usgs.gov; ODUM, J. K., US Geological Survey, Golden, CO, odum@usgs.gov; LIBERTY, L. M., Boise State University, Boise, ID, lml@cgiss.boisestate.edu; PULLAMMANAPPALLIL, S., Optim, Inc., Reno, NV, satish@optimsoftware.com; PRINA, N., University of Nevada, Reno, NV, nick.prina@gmail.com; CASHMAN, P., University of Nevada, Reno, NV, pcashman@mines.unr.edu; TREXLER, J., University of Nevada, Reno, NV, trexler@unr.edu; KENT, R. L., nees@UTexas, Austin, TX, rkent@mail.utexas.edu
In support of the Western Basin and Range Community Velocity Model and the proposed Reno-Carson City Urban Hazard Maps, the U.S. Geological Survey, University of Nevada, Reno (UNR), and nees@UTexas, Austin, collaborated on a high-resolution seismic imaging study of the Truckee Meadows basin in Reno, Nevada, during June 2009. We acquired a reflection profile in south Reno to contribute to our understanding of the basin structure and faults in the area. We used the nees@UTexas minivib I vibrator source on this 3.84-km east-west profile that followed Manzanita Lane, about 4.5 km south of the Truckee River. This profile crossed several previously-mapped Quaternary faults, including the Virginia Lake fault.Additionally, five weight-drop profiles were collected in March 2010 by UNR and Boise State University. Four of these profiles, about 3.5 km, cross the minivib profile. The analysis of all these lines combined will provide us with three-dimensional constraints on the structure of the southern part of the Reno basin.The 3D analysis will involve building a 3D seismic velocity model using first arrival information from all intersecting lines and using that velocity in subsequent processing. This will help resolve out-of-plane reflections not accounted for in preliminary 2D processing. The preliminary seismic processing was influenced by the noisy urban environment for all of these lines, including automatic gain control and spatial filtering to mitigate ambient noise. Preliminary 3D interpretation of these lines show reflections from steeply-dipping strands of the fault zone. The basin depth from preliminary analysis correlates well with previous gravity surveys and well log data. The significant fault detected below downtown Reno, near the Truckee River, extends south to this area, however it seems to be expressed differently. Additional processing and analysis is in progress to determine more about the structural characteristics and look for other faults in the area.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Ghofrani, Hadi
Schedule   Wed 3:15 PM / Oral
Room   Room 204/205
Fore-Arc Versus Back-Arc Attenuation of Earthquake Ground Motion
GHOFRANI, H., University of Western Onatrio, London, ON, Canada, hghofran@uwo.ca; ATKINSON, G. M., University of Western Onatrio, London, ON, Canada, Gmatkinson@aol.com
Understanding of the attenuation of seismic wave amplitudes with distance is a crucial issue for ground-motion prediction equations and seismic hazard analysis. The interplay of parameters controlling attenuation, such as trade-offs between geometrical spreading and an-elastic attenuation, and complications due to regional crustal structure effects, makes its derivation difficult. In this study, we empirically evaluate the influence of regional geologic structure, in particular the attenuation effects of traveling through a volcanic arc region (fore-arc versus back-arc attenuation). In this study, we characterize the behavior of ground-motion attenuation in fore-arc and back-arc regions in Northern Japan. We performed regression analysis of Fourier amplitude spectra (FAS) of five well-recorded Japanese events that occurred very close to the line formed by the volcanic arc. Based on inspection of the data, we assume a hinged bilinear geometric spreading model with a fixed slope of -1 to 70 km, with slope of -0.5 thereafter. Our results show, with a very high level of confidence, that attenuation is greater in the back-arc direction, especially at higher frequencies. The regional Quality factor is similar for fore-arc and back-arc regions for frequencies up to 1 Hz, above which the Q values increase with frequency more rapidly for fore-arc regions than for back-arc regions. The Q values for fore-arc regions (Q = 240 at 1 Hz, increasing to Q = 3890at 10 Hz) are about a factor of two larger than those for back-arc regions (Q = 197 at 1 Hz, increasing to Q = 1670 at 10 Hz) at high frequencies, implying much stronger attenuation as waves travel through the volcanic crustal structure to the back-arc stations. The separation of fore-arc and back-arc travel paths results in a significant reduction in the standard deviation (“sigma”) of ground motion predictions (by as much as 0.05 log10 units), which has important implications for hazard analyses in subduction regions.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Magnani, M.Beatrice
Schedule   Wed 2:45 PM / Oral
Room   Ballroom C
Spatial and temporal distribution of deformation in the Central U.S. from high-resolution reflection data
MAGNANI, M. B., CERI - University of Memphis, Memphis, TN, mmagnani@memphis.edu
The New Madrid seismic zone, in the Central U.S. is one of the most studied intraplate seismic regions in the world and one of the most controversial. Much of the debate hinges on the puzzling lack of present measurable deformation in the area that was struck repeatedly by large magnitude (M>7) earthquakes in the recent past, and that today exhibits high levels of background seismicity (M>1.5). Characterizing and quantifying the deformation in the U.S. continental interior poses a formidable challenge, as strain builds slowly, faults are buried under a blanket of sediments and don’t exhibit a clear morphological signature. High-resolution seismic reflection imaging has been an invaluable tool in identifying buried faults and estimating their slip rates. From two decades of seismic reflection surveying in the Mississippi Embayment, evidence is emerging that the present seismicity does not reflect the deformation pattern in the long term, as substantial amount of Quaternary deformation is accommodated along a network of faults distributed throughout the Embayment, and not just within the NMSZ. Most of these faults are characterized by a long-lived tectonic history, in some cases dating back to the Late Cretaceous, and are comparable in length and amount of offset in the unconsolidated sediments to the New Madrid seismic zone active faults.After twenty year of research effort, is becoming clear that the spatial and temporal distribution of the long-term deformation encompasses a wider region than previously considered, and that a key role in intracontinental deformation might be played by the interaction between faults, rather than by the activity along one isolated fault. Further concerted investigations aimed at identifying the faults and their parameters (timing of events, slip rates, etc) are needed to unravel the dynamics of this interaction.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Guo, Lei
Schedule   Thu AM / Poster
Room   Ballroom B
The New Madrid Seismic Zone Fault System Imaged by High-Resolution Seismic Reflection Data
GUO, L., CERI, University of Memphis, Memphis, TN, lguo2@memphis.edu; MAGNANI, M. B., CERI, University of Memphis, Memphis, TN, mmagnani@memphis.edu; MCINTOSH, K., Institute for Geophysics, University of Texas at Austin, Austin, TX, kirk@ig.utexas.edu; WALDRON, B., Ground Water Institute, University of Memphis, Memphis, TN, bwaldron@memphis.edu; SAUSTRUP, S., Institute for Geophysics, University of Texas at Austin, Austin, TX, steffen@ig.utexas.edu
In the winter of 1811-1812, the Central U.S., were struck by a series of three or four large magnitude earthquakes. Today this region, the New Madrid Seismic Zone (NMSZ) is one of the most active intraplate regions in the world and the present seismicity illuminates four main faults, extending from west of Memphis, TN, into southern Missouri for more than 200 km.In June 2010 ~300 km of high-resolution seismic marine reflection data were acquired along the Mississippi River from Cape Girardeau, MO to Caruthersville, MO to image the system of faults that ruptured during the 1811-1812 earthquakes and that are still active today. The data were acquired using a 15/15 cm3 mini-GI airgun fired at 13.790 MPa, a 24-channel 75 m-long active streamer, with 3.125 m group and 9 m nominal shot interval. The profile crosses two of the four main NMSZ active faults, including the Reelfoot thrust, which is intersected three times along the river by the seismic survey. At these three crossings the data show that to the southeast the reverse offset of 42 m at the top of the Cretaceous along the Reelfoot thrust is accommodated by a single fault, while farther downriver to the northwest, where the Reelfoot thrust approaches the northern dextral strike-slip fault, the compression is accommodated by a series of small faults, suggesting that the Reelfoot fault splits into a system of splays. Where reflectors are well imaged, the data indicate that displacement along the Reelfoot fault increases with age of the sediments involved, implying a repeated reactivation of the fault through time. To the south, the profile images the Cottonwood Grove dextral strike-slip fault. Here the data show that the sedimentary section is faulted at three locations, suggesting that the single fault identified by the seismicity at middle crustal depths (~5-12km) branches upsection to form a flower structure that accommodates the deformation along the southern arm of the seismicity.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Graizer, Vladimir
Schedule   Wed 10:45 AM / Oral
Room   Room 204/205
MODULAR FILTER-BASED APPROACH TO GROUND MOTION ATTENUATION MODELING
GRAIZER, V., U.S. Nuclear Regulatory Commission, Washington, DC, Vladimir.Graizer@nrc.gov; KALKAN, E., U.S. Geological Survey, Menlo Park, CA, ekalkan@usgs.gov
An attenuation relation is a mathematical representation of ground motion signal transformation, due to numerous physical processes, from the earthquake source to a site. We found that a single-degree-of-freedom transfer function approximation, with a combination of filters, is an accurate (that is, providing expected median prediction) and efficient (that is, providing relatively small standard error of prediction) way to model this complex transformation. We are revisiting the commonly used empirical approach to ground motion attenuation modeling, and comparing it with an alternative modular filter-based approach that can be effectively used for predicting ground motion at near- (<10 km), intermediate- (~10 km to 100 km), and far-field distances (>100 km). In this latter approach, each filter is calibrated separately to represent a certain physical phenomenon affecting seismic radiation from the source. This approach allows for relatively fast change of attenuation rate leading to better representation of regional variation in ground motion prediction. We also present our PGA-based predictive model for 5% damped spectral acceleration (SA) ordinates as a continuous function of spectral period allowing calculation of its ordinates at any period of interest within the model range of 0.01 to 10 s and possibly beyond it. We are showing that the Graizer and Kalkan attenuation relation demonstrates good agreement with recorded data from past earthquakes as well as with the NGA relations. The model is designed to predict ground motion parameters from earthquakes with moment magnitudes of 5 to 8 within a distance range of 0 to 250 km (these limitations stem from the NGA dataset utilized). We have tested Graizer and Kalkan attenuation relationship on a global Atlas dataset developed by the USGS ShakeMap group to extend attenuation relationship to larger distances up to 400 km.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Aagaard, Brad
Schedule   Fri 2:30 PM / Oral
Room   Ballroom E
Constraining the Depth Dependence of Fault Constitutive Parameters
AAGAARD, B. T., U.S. Geological Survey, Menlo Park, CA, baagaard@usgs.gov
I investigate constraints on the depth dependence of fault constitutive parameters in dynamic spontaneous rupture models using a wide variety of geophysical data. Seismological observations constrain the spatial and temporal characteristics of slip in earthquake ruptures. Geodetic observations constrain the spatial characteristics of slip in earthquakes as well as the inter-seismic strain accumulation. Laboratory experiments offer empirical relationships for friction as a function of slip, slip rate, and state variables. Geologic and geophysical observations indicate confining pressure increases with depth, but dynamic sliding occurs on slip surfaces a few millimeters wide at a low stress level, consistent with measurements of minimal heat flow.I use a combination of Burridge-Knopoff slider-block models and finite-element models to bound the depth dependence of stress levels and the corresponding parameters in some widely-used fault constitutive models (e.g., slip-weakening friction and rate- and state-friction). With statically-strong and dynamically-weak faults proposed by Lapusta and Rice (2003) as a starting model, I consider realistic depth variations in fault tractions and physical properties. The slider-block models permit calculating the long-term or steady-state depth variation in relative and absolute stress for a given set of model parameters over the entire seismic cycle. The finite-element models are used to investigate 3D and elastoplastic effects. I demonstrate some modifications that are necessary for the statically-strong and dynamically-weak fault model to remain viable for realistic depth variations in the fault tractions and bulkphysical properties.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Wald, David
Schedule   Fri 4:00 PM / Oral
Room   Ballroom D
The Role of PAGER in Improving Global Hazard, Building, and Loss Inventories
WALD, D. J., U.S. Geological Survey, Golden, CO, wald@usgs.gov; JAISWAL, K., U.S. Geological Survey, Golden, CO, ; SO, E., U.S. Geological Survey, Golden, CO, ; GARCIA, D., U.S. Geological Survey, Golden, CO, ; MARANO, K., U.S. Geological Survey, Golden, CO, ; LIN, K., U.S. Geological Survey, Golden, CO, ; HEARNE, M., U.S. Geological Survey, Golden, CO, ; GREENE, M., Earthquake Engineering Research Institute, Oakland, CA, ; D’AYALA, D., University of Bath, Bath, UK;CROWLEY, H., EUCENTER, Pavia, Italy; GAMBA, P., EUCENTER, Pavia, Italy; PORTER, K., University of Colorado, Boulder, CO
The Prompt Assessment of Global Earthquakes for Response (PAGER) system now plays a primary alerting role for global earthquake disasters as a part of the U.S. Geological Survey’s (USGS) response protocol. Moreover, as an open, global system, the underlying research and database developments that inform PAGER also support the wider user and modeling communities through continuing and collaborative efforts. Loss estimation and risk assessment require assignment or knowledge of a number of interdependent variables relating hazard to exposure and then to losses, yet it is extremely difficult to directly determine causal relations among ground motion levels, building damage, occupancy, and casualties. PAGER has made a number of significant contributions to this end, particularly those related to providing the means for loss calibration through the association of hazard components with building inventories, their vulnerabilities, and the observed losses. Collaboration with Cambridge University on their Earthquake Impact Database (CEQID) now allows a standardized association of ground shaking, via ShakeMap’s Atlas, with earthquake consequences. Likewise, for building exposure and vulnerability, ongoing USGS PAGER collaboration with the Earthquake Engineering Research Institute’s (EERI) World Housing Encyclopedia (WHE) has helped produce a global, country-specific, building inventory. These and several other efforts mutually support PAGER and the developing Global Earthquake Model (GEM). Notably, components of the PAGER system underpin efforts on GEM’s risk analyses through several of GEM’s global risk components: global earthquake consequences, global exposure, and building vulnerability databases. We discuss these components and ongoing efforts to show how these building blocks for global risk analyses have been significantly improved over the past several years, advancing our ability to estimate and understand the main contributions to global earthquake losses.
Session:Geometry effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Presenter   Sánchez-Sesma, Francisco
Schedule   Wed 4:15 PM / Oral
Room   Room 204/205
On the Energy Partition amongst Elastic Waves for Dynamic Surface Loads in a Semi-Infinite Solid
SÁNCHEZ-SESMA, F. J., Instituto de Ingeniería, Universidad Nacional Autónoma de México, Coyoacán, DF, Mexico, sesma@servidor.unam.mx; WEAVER, R. L., Department of Physics, University of Illinois, Urbana, IL, r-weaver@uiuc.edu; KAWASE, H., Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, Japan, kawase@zeisei.dpri.kyoto-u.ac.jp; MATSUSHIMA, S., Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, Japan, matsushima@zeisei.dpri.kyoto-u.ac.jp; LUZON, F., Departamento de Física Aplicada, U de Almería, Cañada de San Urbano s/n, Almería, Spain, fluzon@ual.es; CAMPILLO, M., Université Joseph Fourier, Grenoble, France, Michel.Campillo@obs.ujf-grenoble.fr; PEREZ-GAVILÁN, J. J., Instituto de Ingeniería, Universidad Nacional Autónoma de México, Coyoacán, DF, Mexico, jjpge@pumas.iingen.unam.mx
The energy partition amongst elastic waves for a dynamic normal load on the surface of an elastic half-space with Poisson ratio of 1/4 is a well known result by Miller and Pursey (1955). The partitions for other Poisson ratios and the corresponding partitions for a dynamic tangential load are less well known. The partitions for the normal and tangential loads were computed independently by Weaver (1985) against Poisson ratio (between 0 and 1/2) using diffuse field concepts and within the context of ultrasonic measurements. This partially explains why the results did not reach the seismological and engineering literature.It can be demonstrated that the energies injected into the elastic half-space by concentrated normal and tangential harmonic surface loads are proportional to the imaginary part of the corresponding components of the Green’s tensor when both source and receiver coincide. The character of the radiation of these two cases is quite different; for a normal load about 2/3 of energy leave the loaded point as Rayleigh surface waves, on the other hand, the tangential load induces a similar amount in the form of body shear waves.These partitions are deterministic. Regarded in connection to the Green function retrieval from averaging cross correlations, results have significant implications for the explanation of the energy densities at the surface of a layered half-space. We use Miller and Pursey (1955) and Weaver (1985) results to calibrate a numerical integration scheme in frequency domain. Partitions also allow obtaining a plausible physical explanation to observed effects in terms of elastic wave propagation and average response under stochastic, diffuse excitation.
Session:Seismotectonics and Hazards of Active Margins in the Circum-Caribbean Sea and Eastern Pacific Ocean
Presenter   Zaliapin, Ilya
Schedule   Wed 11:00 AM / Oral
Room   Ballroom D
Correlations Between Clustering and Productivity Properties of Seismicity in California and Heat Flow
ZALIAPIN, I., University of Nevada, Reno, NV, zal@unr.edu; BEN-ZION, Y., University of Southern California, Los Angeles, CA,
Discovering genuine spatio-temporal seismicity patterns that characterize local regions beyond the classical large-scale average patterns remains an extremely challenging problem of statistical seismology. Of particular importance are patterns that can be related to key physical processes associated with specific properties of faults and the lithosphere. This study focuses on seismic productivity vs. regional heat flow. We compare aftershock and foreshock productivity within statistically significant clusters in California (Zaliapin et al., 2008) with heat flow and general rock type (crystalline vs. deep sedimentary basins), which serve as proxies for the effective viscosity of the crust (Ben-Zion and Lyakhovsky, 2006). We find that (i) relatively cold regions with crystalline rock in the seismogenic zone have high aftershock productivity and low foreshock productivity, and vice versa (ii) regions with high heat flow and deep sedimentary basins have increased foreshock activity and reduced aftershock productivity. A detailed spatio-temporal analysis of seismic productivity for California shows that seismic productivity is characterized by high spatial variability, positively correlated with the local heat flow where data is available, and at the same time it is temporally stable. Our findings are consistent with the global earthquake productivity analysis on a much coarser scale. The results of this work can be used to develop refined estimates of seismic shaking hazard and associated with individual fault zones as well as region-specific earthquake forecast approaches.
Session:Seismic Sources and Parameters
Presenter   Bohnhoff, Marco
Schedule   Wed AM / Poster
Room   Ballroom B
Seismicity of the East Anatolian Fault Zone: Insights into structural variation and fault kinematics
BULUT, F., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, bulut@gfz-potsdam.de; BOHNHOFF, M., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, ; EKEN, T., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, ; JANSSEN, C., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany, ; KILIÇ, T., Directorate of Disaster Affairs, Ankara, Turkey, ; DRESEN, G., Deutsches GeoForschungsZentrum GFZ, Potsdam, Germany,
The East Anatolian Fault Zone (EAFZ) represents an inter-plate boundary extending over ~500 km between the Arabian and Anatolian plates. Relative motion of the plates occurs with slip rates of about 9±1 mm/y resulted in destructive earthquakes in Eastern Turkey as documented by historical records. We investigate fault segmentation of the EAFZ as well as interaction of sub-segments by combining data from available regional seismic stations operated by Kandilli Observatory Earthquake Research Institute and the Directorate of Disaster Affairs to achieve the best possible hypocenter locations. We optimized a reference 1-D velocity model using a grid-search approach and re-located hypocenters using the Double-Difference earthquake relocation technique. The refined hypocenter map provides insights into the internal deformation within the fault zone down to a resolution of about 0.5 km. The distribution of hypocenters suggests that the EAFZ is characterized by NE-SW and E-W oriented sub-segments that slightly deviate from its overall trend. The main fault is surrounded by sub-parallel aligned hypocenters possibly representing fault-normal and fault-parallel oriented subsidiary faults. Structural variation along the EAFZ significantly affects faulting mechanisms along the fault zone. Fault mechanisms indicate predominantly left-lateral strike slip which turns into normal/thrust faulting depending on fault orientation and present state of tectonic loading. Spatiotemporal evolution of hypocenters indicates a systematic migration of micro- and moderate-sized earthquakes from main fault into adjacent fault segments within several days documenting progressive interaction between the major branch of the EAFZ and its secondary structures.
Session:The Seismo-Acoustic Wavefield
Presenter   Gibbons, Steven
Schedule   Fri 3:30 PM / Oral
Room   Ballroom C
The Infrasonic Wavefield at Regional Distances from Repeating Seismo-Acoustic Events
GIBBONS, S. J., NORSAR, Kjeller, Norway, steven@norsar.no
The Finnish military detonate expired ammunition in a sequence of between 10 and 60 explosions every year. The ARCES array, at a distance of 178 km, records strong seismic signals from each event. Near identical signals demonstrate that the almost co-located events have a simple source-time function and are similar in yield. They also facilitate event detection using a correlation detector. Coupled infrasonic signals are observed on the seismic sensors for almost every event and non-observation of infrasound is usually attributed to exceptionally high noise levels or unrelated seismic signals.Reprocessing ARCES data throughout the archive has identified approximately 500 such events since 1988. Numerous events display presumed tropospheric arrivals after around 500 seconds. Almost all are associated with longer duration signals at around 600 seconds, presumed stratospheric arrivals, although these "shadow zone" observations are seldom predicted by ray-tracing. A few events are associated with presumed thermospheric arrivals at around 900 seconds with shorter duration, smaller amplitude, higher apparent velocity, and a lower frequency content. The sequences in 2008, 2009, and 2010 were also recorded by a temporary microbarograph mini-array within ARCES with a lower detection threshold than on the seismic sensors. This has indicated a longer duration for the stratospheric signals given that only the largest amplitudes are recorded on the seismometers. The new data also suggests that far more thermospheric arrivals than first assumed.The microbarograph mini-array has detected many low amplitude infrasound signals from numerous different seismo-acoustic sources in the European Arctic. Many of these are associated with several hundreds of events, and it is a focus of ongoing research to map out the active sources and characterize the variability of the associated infrasonic wavefield as a function of time, range, and direction.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Newman, Andrew
Schedule   Thu 8:30 AM / Oral
Room   Ballroom D
The 25 October 2010 Mentawai Tsunami Earthquake, from Real-time Discriminants, Finite-fault Rupture, and Tsunami Excitation
NEWMAN, A. V., Earth & Environmental Sciences, Georgia Institute of Technology, Atlanta, GA, anewman@gatech.edu; HAYES, G., National Earthquake Information Center, US Geological Survey, Golden, CO, ; WEI, Y., Pacific Marine Environment Lab, NOAA, Seattle, WA, ; CONVERS, J. A., Earth & Environmental Sciences, Georgia Institute of Technology, Atlanta, GA,
The moment magnitude 7.8 earthquake that struck offshore the Mentawai islands in western Indonesia on 25 October 2010 created a locally large tsunami that caused more than 400 human causalities. We identify this earthquake as a rare slow-source tsunami earthquake based on: 1) disproportionately large tsunami waves; 2) excessive rupture duration near 125 s; 3) large shallow slip (8+m) determined through finite-fault modeling; and 4) deficiencies in energy-to-moment and energy-to-duration-cubed ratios, the latter determined in near-real time. We detail the real-time energy calculations that identified the slow-nature of this event. Using the rupture velocity determined from finite fault modeling we applied straightforward corrections to slip models and show how reduced crustal rigidities along the shallow trench contributed to increased slip, causing the 5-9 m local tsunami run-up and observed transoceanic wave heights observed 1600 km to the southeast.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Upegui Botero, Fabio M
Schedule   Fri AM / Poster
Room   Ballroom B
The May 16, 2010 Mw. 5.8 Puerto Rico Earthquake: Site Characterization, Local Site Effects, and Joint Time-Frequency Analysis
UPEGUI-BOTERO, F. M., University of Puerto Rico, Mayaguez, PR, fabio.upegui@upr.edu; HUERTA-LOPEZ, C. I., University of Puerto Rico at Mayaguez/CICESE, Ensenada, BC Mexico, carlos.huerta@upr.edu; CARO-CORTES, J. A., University of Puerto Rico, Mayaguez, PR, andres.caro@upr.edu; ROMAN-BATISTA, R. E., University of Puerto Rico, Mayaguez, PR, ruth.roman1@upr.edu; MARTINEZ-CRUZADO, J. A., University of Puerto Rico, Mayaguez, PR, jose.martinez44@upr.edu; SUAREZ-COLCHE, L. E., University of Puerto Rico, Mayaguez, PR, luis.suarez3@upr.edu
On May 16 2010, at 05:16:10 (UTC), the northwest area of the Puerto Rico Island was struck by a moderate-sized earthquake (Mw. 5.8). It was felt in the eastern Dominican Republic, the Virgin Islands and all over the Puerto Rico Island. The earthquake was recorded by 63 accelerographic stations of the Puerto Rico Strong Motion Program (PRSMP) distributed around the island. Only free-field stations seated on soil or rock were used in this study. In the first stage, the accelerograms were analyzed following the well established data processing procedure for acceleration strong motion records through volume I to III, and the Power Spectral Density (PSD’s) was computed. Secondly, a joint time-frequency analysis was carried out using different time-frequency distributions. The aim of the joint time-frequency spectral decomposition is to assess the strength of the signal energy as a function of the variables frequency “f” and time “t”, in order to generate a distribution which appropriately identifies the energy distribution in the time-frequency plane. The following Cohen class distributions were applied: (i) Short Time Fourier Transform (STFT), (ii) Wigner-Ville Distribution (WVD), (iii) Choi-Williams Distribution (CWD), (iv) Reduced Interference Distribution (RID), and (v) Adaptive Optimal Kernel (AOK ). Each of these distributions was applied to the recorded data and a comparison among them was analyzed. Finally, an experimental and numerical modeling of H/V spectral ratio (HVSPR) was performed to characterize the sites in terms of the fundamental vibration frequency, the subsoil geometry and physical properties. The adopted procedure for the site characterization in terms of the subsoil geometry and physical properties was through an iterative forward modeling process until the lowest residual between the experimental and the theoretical HVSPR of the fundamental vibration mode was obtained.
Session:Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Presenter   Leonard, Mark
Schedule   Thu 1:45 PM / Oral
Room   Ballroom C
Spatio-temporal Complexity of Seismicity in Stable Cratonic Core: Seismological, Geological and Geodetic Evidence for Long-term Migratory Behaviour of Seismicity in the SW of Australia
LEONARD, M., Geoscience Australia, Canberra, ACT, Australia, mark.leonard@ga.gov.au; CLARK, D., Geoscience Australia, Canberra, ACT, Australia, dan.clark@ga.gov.au; GRIFFIN, J., Geoscience Australia, Canberra, ACT, Australia, Jonathan.griffin@aifdr.org
An optimal combination of geological, geomorphological and climatic properties makes the SW corner of Australia an excellent natural laboratory for earthquake behaviour studies in SCC. Fault scarps from >M6.4 earthquakes in this region are preserved in the landscape for up to 100ka. Recently, 37 landscape features interpreted to be fault scarps have been identified. These are considered to have been formed by 70+ earthquakes ranging from M5.9 to M7.3, the oldest of which is likely to be older than 100 ka. The seismicity rate estimated from this palaeo-catalogue is an order of magnitude higher than the contemporary seismicity. The topography and widespread exposure of bedrock in this region has facilitated the establishment of a high precision GPS-geodetic network. The results of campaign occupations in 2002 and 2006 suggest that the long term tectonic strain-rate is approximately 7.5 times less than the seismicity recorded over the past 60 years, which itself is 2-5 times the seismicity rate of the 60 years prior to 1950. These results are consistent with emerging models of the behaviour of intra-continental faults. Palaeoseismic data indicates that SCR faults display temporal clustering of surface-rupturing events, with clusters of several events, being separated by quiescent periods of 100-1000 ka, or more. At a larger scale, the distribution, geometry and spacing of scarps is consistent with a model whereby the ductile part of the lithosphere deforms uniformly in response to an contractional strain, and the upper (seismogenic) layer accommodates this large scale flow by localised, transient and recurrent brittle deformation along lines of pre-existing crustal weakness. The net effect being that over the long term the whole Precambrian craton could be considered as a single seismic source zone with a >M5.9 expected every 150 years. We expect that this model might hold for SCC regions across Australia, and likely holds for similar SCC regions of the world.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Grant Ludwig, Lisa
Schedule   Thu 11:30 AM / Oral
Room   Room 204/205
Toward an Understanding of the Gap between Earthquake Science and Local Policy-Makers in Orange County, California
RUNNERSTROM, E. E., School of Social Ecology, University of California, Irvine, Irvine, CA, ; GRANT LUDWIG, L., Program in Public Health, University of California, Irvine, Irvine, CA, lgrant@uci.edu
This study measured the extent to which earthquake science was used for loss mitigation by local-level governments in Orange County, California, as of 2003. A list of earthquake-science research products that are useful for mitigating earthquake losses was compiled using (1) General Plan Guidelines issued by the State of California’s Office of Planning and Research, and (2) the Communication, Education, and Outreach Program of the Southern California Earthquake Center. For local-level planning, the Safety Element chapter of California cities’ General Plans is the overarching document that contains text, graphics, and figures which together compose a set of programs, goals, and policies for mitigating earthquake losses. The study followed a descriptive line of empirical inquiry procedures by administering an enumerative survey upon a cross-section of one-group of archived Safety Element documents whose analyzed content was recorded in a tabular review format. A non-probability, purposive sample of thirty-four participants was selected for this study. Each participant is one of thirty-four cities in Orange County, as of year-end 2003. The content of each participant’s Safety Element was analyzed in two phases. The first phase determined which items of earthquake-science research products were involved. The second phase extracted the programs, goals, and policies from the Safety Elements and then classified them according to emergent categorical schemes, which were enumerated in a descriptive, summary form. These methods should (1) identify the general use of earthquake-science research as a group of products used by city planners in California, (2) enumerate the extent to which specific products are being used, and (3) summarize earthquake-loss-mitigation programs, goals, and policies that are maintained by Safety Elements. Results suggest there is a gap between science and utilization of science for seismic mitigation policy at local government levels.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Clark, Daniel
Schedule   Fri 1:45 PM / Oral
Room   Ballroom D
Mmax variation across the Australian stable continental region (SCR) crust derived from the Quaternary faulting record
CLARK, D. J., Geoscience Australia, Canberra, ACT, Australia, dan.clark@ga.gov.au; MCPHERSON, A. A., Geoscience Australia, Canberra, ACT, Australia, andrew.mcpherson@ga.gov.au; COLLINS, C. D. N., Geoscience Australia, Canberra, ACT, Australia, clive.collins@ga.gov.au
Probabilistic seismic hazard analyses (PSHAs) require an estimate of Mmax, the magnitude (M) of the largest earthquake that is thought possible within a specified area. In seismically active areas such as some plate boundaries, large earthquakes occur frequently enough that Mmax might have been observed directly during historic times. In less active regions like Australia, and most of the Central and Eastern United States and adjacent Canada (CEUSAC), large earthquakes are much less frequent and generally Mmax must be estimated indirectly.By virtue of a fortuitous combination of climatic conditions, geology and geomorphology, Australia boasts arguably the richest Quaternary faulting record of all the world’s SCR crust. Extensive consultation amongst the geological community, and recent advances in digital elevation data coverage, have allowed the compilation of an inventory of over 200 landscape features consistent with fault scarps relating to Quaternary surface rupturing earthquakes across Australia. Variations in the character of these scarps, when considered together with large-scale geological and geophysical variations, justify the division of the continent into six onshore ‘neotectonic domains’. Within each domain Mmax has been calculated from the 75th percentile scarp length by averaging the earthquake magnitudes predicted by several published relations. Results range from M7.0–7.5±0.2. While this approach is inherently conservative, it means extreme values that may relate to multiple event scarps, which cannot be confidently discriminated without field validation, are excluded. Consequently, in several cases our method underestimates Mmax by 0.1-0.2 magnitude units relative to calculations based upon rare palaeoseismic data. Nonetheless, our findings indicate the potential for M>7.0 earthquakes across Australia – and by proxy analogous crust in the CEUSAC and elsewhere – and thus provide a means of significantly reducing uncertainty in PSHAs.
Session:Combining Geodetic and Seismic Measurements
Presenter   Melgar, Diego
Schedule   Fri 8:30 AM / Oral
Room   Ballroom E
Strong Motion Displacement and Velocity Seismograms
MELGAR, D., Scripps Institution of Oceanography, La Jolla, CA, dmelgarm@ucsd.edu; BOCK, Y., Scripps Institution of Oceanography, La Jolla, CA, ; CROWELL, B. W., Scripps Institution of Oceanography, La Jolla, CA, ; JACKSON, M., UNAVCO, Boulder, CO., ; ALLEN, R. M., University of California Berkeley, Berkeley, CA,
Obtaining strong motion displacement and velocity waveforms remains an open problem in seismology. Traditionally they are obtained by integration, polynomial fitting and filtering of acceleration records. The low frequency components (including the static deformation) of these waveforms are not accurately determined. Additionally there is no objective way of determining the correction parameters and they have to be tailored by each researcher to what “works best” for every station-event pair. This hinders the automation of the process, the application to large networks, and real-time processing. We demonstrate a new technique that employs a multi-rate Kalman filter to fuse data from accelerometers and GPS instruments with different sampling rates in order to obtain real-time total (dynamic and static) displacements and velocities. We demonstrate the filter performance in two real world settings: (1) the 2010 Mw 7.2 El Mayor-Cucapah earthquake with 100 Hz strong motion recordings and 1 Hz GPS data, at collocated stations as far as 300 km from the epicenter. (2) the 2003 Mw 8.3 Tokachi-Oki earthquake with collocated 200 and 100 Hz strong motion recordings and 1 Hz GPS data over a wide region. We will discuss the spectral characteristics of the resulting waveforms and show that obtaining them in real time or near real time is feasible. We conclude that this formulation is superior to traditional methodologies by providing total displacement and velocity waveforms at the sampling rate of the accelerometers, and can be used to determine timelier earthquake source parameters. To this end, we have proposed to the NSF EarthScope program that GPS real-time capability should be enhanced in the Western U.S., additional collocations of GPS and accelerometers should be undertaken, and integrated on-the-fly processing of both data streams should be performed at dual analysis centers.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Clark, Daniel
Schedule   Thu 8:45 AM / Oral
Room   Ballroom C
Long term behaviour of Australian stable continental region (SCR) faults and implications for earthquake hazard assessment
CLARK, D. J., Geoscience Australia, Canberra, ACT, Australia, dan.clark@ga.gov.au; MCPHERSON, A. A., Geoscience Australia, Canberra, ACT, Australia, andrew.mcpherson@ga.gov.au; VAN DISSEN, R., GNS Science, Lower Hutt, New Zealand, R.VanDissen@gns.cri.nz
Australia boasts arguably the richest Quaternary faulting record of all the world’s SCR crust. Extensive consultation with the earth science community, and recent advances in digital elevation data coverage, have allowed the compilation of an inventory of over 200 landscape features consistent with fault scarps relating to Quaternary surface rupturing earthquakes. This record, together with a growing database of palaeoseismological measurements, permits analysis of the long term behaviour of SCR faults in different geologic settings. Details of variations in palaeoearthquake magnitude (including maximum magnitude), recurrence characteristics (given appropriate scaling relations and assumptions relating to landscape modification rates) and spatial relationships between scarps in different deforming regions are recoverable. On this basis, six onshore neotectonic domains are defined.A common characteristic across Australia appears to be the temporal clustering of large earthquakes - periods of earthquake activity comprising a finite number of large events are separated by much longer periods of seismic quiescence. This episodic behaviour poses problems for probabilistic seismic hazard assessments (PSHAs) in that it implies that large earthquake recurrence is not random (i.e. Poissonian). The points critical to understanding the hazard posed by SCR faults, and modelling this hazard probabilistically, become: 1) is the fault in question about to enter an active period, in the midst of an active period, or in a quiescent period; 2) how many large events might constitute an active period, and how many ruptures has the fault generated so far in its current active period (should it be in one); and 3) what is the mean recurrence interval in an active period, and what is the variability around this mean? This mean can be incorporated statistically into PSHAs and must be considered when palaeoearthquake catalogues are combined with historic records.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Iwata, Tomotaka
Schedule   Thu AM / Poster
Room   Ballroom B
Validation of Characterized Source Model of Intraslab Earthquakes for Strong Ground Motion Prediction
IWATA, T., DPRI, Kyoto University, Uji, Kyoto, Japan, iwata@egmdpri01.dpri.kyoto-u.ac.jp; ASANO, K., DPRI, Kyoto University, Uji, Kyoto, Japan, k-asano@egmdpri01.dpri.kyoto-u.ac.jp; SEKIGUCHI, H., DPRI, Kyoto University, Uji, Kyoto, Japan, Haruko.Sekiguchi@ky8.ecs.kyoto-u.ac.jp
We proposed a prototype of procedure for strong ground motion prediction of intraslab earthquakes. It is based on the characterized source model of intraslab earthquakes constructed by the slip characterization of heterogeneous source models and the relationships between SMGA and asperity. Iwata and Asano (2010) obtained the empirical relationships of rupture area (S) and total asperity area (Sa) to seismic moment as follows, with assuming power of 2/3 dependency of S and Sa on seismic momentS (km**2) = 6.57 10**(-11) M0**(2/3) (Nm) (1)Sa (km**2) = 1.04 10**(-11) M0**(2/3) (Nm) (2)We also checked the SMGA approximately corresponds to the asperity area for several events. Based on the empirical relationships obtained above, we gave a procedure for constructing source models for intraslab earthquakes for strong motion prediction. [1] Give the seismic moment M0.[2] Obtain total rupture area and total asperity area according to the empirical scaling relationships between S, Sa, and M0 given by Iwata and Asano (2010).[3] Square rupture area and asperity are assumed.[4] Source mechanism is assumed to be same as that of small events in the source region.[5] Plural scenarios including variety of number of asperities and rupture starting points are prepared.We are testing this procedure by simulating strong ground motions for several observed events.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Asano, Kimiyuki
Schedule   Wed PM / Poster
Room   Ballroom B
Validation of Velocity Structure Model for Long-Period Ground Motion Simulation in Southwestern Japan Using Green’s Functions Extracted by Seismic Interferomerty
ASANO, K., Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto, Japan, k-asano@egmdpri01.dpri.kyoto-u.ac.jp; IWAKI, A., Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto, Japan, iwaki@egmdpri01.dpri.kyoto-u.ac.jp; IWATA, T., Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto, Japan, iwata@egmdpri01.dpri.kyoto-u.ac.jp
An M8-class mega-thrust earthquake (Nankai earthquake) is expected to occur along the Nankai subduction zone, southwestern Japan (e.g., Headquarters for Earthquake Research Promotion, 2009). Development of the crustal velocity structure model along the propagation path is an essential part in ground motion prediction for such mega-thrust events. As for southwestern Japan, Iwata et al. (2008) have proposed a three-dimensional crustal velocity structure model including the subducting slab constructed by compiling seismic profiles and other seismic information. Recently, the seismic interferometry technique using continuous ambient noise records has been widely applied to many aspects of seismology (e.g., Campillo and Paul, 2003). It has been also used to test the performance of velocity models (e.g., Ma et al., 2008). We applied the seismic interferometry to the continuous records of 24 F-net broadband seismograph stations operated by NIED, Japan, to retrieve inter-station Green’s functions in the period range between 2 and 10 s, which is a typical period range for long-period ground motion prediction. The continuous data are divided into one-hour-long segments. Cross-correlation for each station-pair within 400 km is computed for each segment after temporal one-bit normalization. All the cross-correlations are stacked over one year to extract coherent signals among the stations. Clear propagating signals, which have the characteristics of Rayleigh wave, are recognized from the observed inter-station Green’s functions.Then, we are testing the crustal velocity model of Iwata et al. (2008) by comparing the observed Green’s functions with the synthetics from the model. The original shear-wave velocity in the uppermost crust of Iwata et al. (2008) model is 2.7 km/s. Our current results suggest that faster shear-wave velocity is necessary to explain the observed travel time and waveform characteristics of Rayleigh wave retrieved by this study.
Session:Geometry effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Presenter   Pilz, Marco
Schedule   Wed 4:30 PM / Oral
Room   Room 204/205
Observed and Simulated Basin-related Effects on Ground Motion in the Santiago de Chile Basin
PILZ, M., Helmholtz center Potsdam - GFZ, Potsdam, Germany, pilz@gfz-potsdam.de; PAROLAI, S., Helmholtz center Potsdam - GFZ, Potsdam, Germany, parolai@gfz-potsdam.de; STUPAZZINI, M., MunichRe, Munich, Germany, MStupazzini@munichre.com; PAOLUCCI, R., Politecnico di Milano, Milano, Italy, paolucci@stru.polimi.it
Simulations of strong ground motion within the Santiago de Chile Metropolitan area were carried out by means of the spectral element technique. The city is located on the top of a low-velocity sedimentary basin with pronounced sediment-bedrock interface and is further surrounded by steep mountains. To this regard, a 3D model including surface topography and basement structure was derived for the basin. The simulation of a regional event, which has also been recorded by a dense network which had been installed in the city of Santiago for recording aftershocks of the 27 February 2010 Maule earthquake, highlights a strong dependence of spectral amplification in the basin on site conditions. Moreover, the comparison between observations and synthetic seismograms indicates that the model is capable to realistically calculate ground motion in terms of amplitude, duration, and frequency. The simulations clearly show focusing and defocusing of waves, significantly influenced by the basin structure, and their correlation with structural damage intensity and spatial distribution. Examination of the dependency of ground motion on the hypocenter location for a hypothetical event occurring along the active San Ramón fault, which is crossing the eastern outskirts of the city, shows that the unfavorable interaction between fault rupture, radiation mechanism, and complex geological conditions in the near-field may give rise to large values of peak ground velocity. By comparing our results with classical scenario next generation attenuation (NGA) models we draw conclusions about the level of seismic risk for Santiago de Chile and about where NGAs fail.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Campillo, Michel
Schedule   Thu 10:45 AM / Oral
Room   Ballroom D
Slow slip, speed change and tremors in the Guerrero gap.
RIVET, D., Isterre, Université Joseph Fourier and CNRS, Grenoble, France, diane.rivet@gmail.com; RADIGUET, M., Isterre, Université Joseph Fourier and CNRS, Grenoble, France, Mathilde.Radiguet@ujf-grenoble.fr; CAMPILLO, M., Isterre, Université Joseph Fourier and CNRS, Grenoble, France, ; SHAPIRO, M., IPGP, Paris, France, nshapiro@ipgp.fr; CRUZ-ATIENZA, V., UNAM, Mexico City, Mexico, cruz@geofisica.unam.mx; COTTE, N., Isterre, Université Joseph Fourier and CNRS, Grenoble, France, Nathalie.Cotte@ujf-grenoble.fr; KOSTOGLODOV, V., UNAM, Mexico City, Mexico, ; G-GAP Team.
The so-called Guerrero gap is a segment of the Mexican subduction zone where no large thrust earthquake (Mw>7) occurred during more than a century. The question of the recurrence of large earthquakes on this segment is a key issue for seismic risk evaluation in the region. Guerrero is a place where large slow slip events have been detected regularly (2002, 2006, 2010) and non-volcanic tremors are observed. The Mexican-French project G-GAP aims at studying the geodetic and seismological signals in the region to enlighten the complex mechanical behavior of this convergent margin. The geometry of this subduction zone is well constrained and we used kinematic inversion of continuous GPS time series to describe the slip evolution during the slow slip events (Radiguet et al., 2010). We performed numerical modeling of the deformation in the crust induced by the 2006 slow slip event. We also observed a temporal change of seismic speed in the deep crust from ambient noise analysis, with a maximum of relative drop (0.2%) concomitant with the maximum of slip rate obtained in the kinematic slip model of the slow slip event. We show the tremor activity during the period of 2005-2007 including the 2006 slow slip event (Kostoglodov et al. 2010) and discuss the tremors locations with respect to deformation at depth.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Chen, Kou-Cheng
Schedule   Fri AM / Poster
Room   Ballroom B
Site Amplification in Northern Taiwan Estimated from an Intermediate Depth Earthquake
CHEN, K. C., Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, chenkc@earth.sinica.edu.tw; WANG, J. H., Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, jhwang@earth.sinica.edu.tw; WU, C. F., Seismological Observation Center, Central Weather Bureau, Taipei, Taiwan, wucf@scman.cwb.gov.tw
On 1 June 2008, an intermediate depth earthquake (depth 92.3 km, ML5.8, Mw5.1) occurred in northern Taiwan. This earthquake was well recorded by the Taiwan Strong Motion Instrumentation Program (TSMIP) accelerograph network. The averaged Fourier amplitude spectrum of the shear wave from two horizontal ground accelerations for the Class-B site is lower than that of Class-C, Class-D, and Class-E sites at frequency less than 9 Hz, while very close to each other at frequency greater than 9 Hz. Preliminary results from spectral ratios of the soft soil sites to the averaged Class-B site show that amplification of ground motion in the Taipei and Ilan basins can enlarge up to 10 times. The contour map of spectral ratio is consistent with that of the peak ground accelerations for this intermediate depth earthquake.
Session:The Seismo-Acoustic Wavefield
Presenter   Evers, Läslo
Schedule   Fri 2:45 PM / Oral
Room   Ballroom C
An Overview of Seismo-acoustic Studies in Northwestern Europe
EVERS, L. G., KNMI, De Bilt, the Netherlands, evers@knmi.nl; FRICKE, J. T., KNMI, De Bilt, the Netherlands, fricke@knmi.nl; SMETS, P., KNMI, De Bilt, the Netherlands, pieter.smets@knmi.nl; VAN GEYT, A., KNMI, De Bilt, the Netherlands, anton.van.geyt@knmi.nl
In recent years, a series of accidental explosions in Europe have been studied. A high-pressure gas pipeline exploded in Belgium in 2004. Both infrasound and seismic signals were observed and analyzed to reveal source characteristics like location, yield and signal duration. One of the most studied seismo-acoustic events occurred in the UK in 2005, where a vapor cloud exploded after the overflow of an oil depot. Infrasound and seismic signals were detected on seismometers in the UK and were used to assess the accuracy of the derived origin time by evaluating the propagation through both the solid earth and atmosphere. In the far field, infrasound signals observed in the Netherlands showed an unusual pattern. It appeared that the acoustic phases were guided by a stratospheric jet of up to 180 m/s, leading to exceptionally fast arrivals which were labeled as forerunners. Such anomalous behavior had earlier been observed in the Russian Federation by Dr. S. Kulichkov and is further studied in collaboration with the NCPA (Olemiss). Not only the polar vortex wind highly influences the propagation, also the temperature can lead to anomalous propagation. Stratospheric refractions of infrasound signals detected in the Netherlands, after a domestic explosion in Belgium in 2010, arrived at a very short range. The classical shadow zone for stratospheric arrival is around 200 km, in this case a shadow zone of 100 km was formed due to a minor Sudden Stratospheric Warming. Although the stratosphere plays a dominant role in long range propagation (> 200 km), tropospheric phases are also studied which appear on both seismic and infrasound stations in the Netherlands due to (local) military practices like supersonic flying and weapon tests.This presentation will give an overview of some of these recent observations and highlight the lessons learned from seismo-acoustic analyses.
Session:Creative Wavefield Recording and Analysis
Presenter   Malek, Jiri
Schedule   Fri 10:30 AM / Oral
Room   Ballroom E
Rotational Seismic Shear Wave Generator for Seismic Surveying
MALEK, J., Institute of Rock Structure and Mechanics ASCR, Czech Republic, malek@irsm.cas.cz; BROKESOVA, J., Charles University, Faculty of Mathematics and Physics, Czech Republic, Johana@karel.troja.mff.cuni.cz; KOLINSKY, P., Institute of Rock Structure and Mechanics ASCR, Czech Republic, kolinsky@irsm.cas.cz
Two prototypes of mechanical Generator of pure transverse S-wave and seismic rotational motions are presented. Generator is anchored with its fixed part in the ground, and the mobile (rotary) part of the Generator, after being activated, is stopped instantaneously by the braking mechanism; this instantaneous stopping transmits energy into the rock massif. The forces equivalent to this source represent the well known center of rotation. An advantage of the Generator is its relatively small dimensions and weight, which makes it easy to move it in the field. The Generator is designed to be used for sequentially repeated experiments, so that essentially the same pulse of rotational seismic waves is generated. The signals from repeated measurements may also be combined in the control unit in order to achieve high sensitivity by suppressing noise via stacking. Non-linear combination of signals can be applied for this purpose. The Generator is intended for use in a measuring set together with mechanical rotational sensor system (Rotaphone). The example of application of the device demonstrates rotational components produced by the generator pulses and their propagation through shallow geological structure beneath the Generator. The results agree with theoretical radiation pattern for center of rotation.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Crone, Anthony J.
Schedule   Fri 3:45 PM / Oral
Room   Ballroom E
Integration of Paleoseismic Data from Multiple Sites to Develop an Objective Earthquake Chronology: Application to the Weber Segment of the Wasatch Fault Zone, Utah
DUROSS, C. B., Utah Geological Survey, Salt Lake City, UT, christopherduross@utah.gov; PERSONIUS, S. F., U.S. Geological Survey, Denver, CO, personius@usgs.gov; CRONE, A. J., U.S. Geological Survey, Denver, CO, crone@usgs.gov; OLIG, S. S., URS Corporation, Oakland, CA, Susan_Olig@URSCorp.com; LUND, W. R., Utah Geological Survey, Cedar City, UT, billlund@utah.gov
We present a method to evaluate and integrate paleoseismic data from multiple sites into a single, objective measure of earthquake timing and recurrence on discrete segments of active faults. We apply this method to the Weber segment of the Wasatch fault zone using data from four fault-trench studies completed in the past three decades. After systematically reevaluating the stratigraphic and chronologic data from each trench site, we constructed time-stratigraphic OxCal models, which yield site probability density functions (PDFs) of the times of individual earthquakes. We next correlated the site PDFs into a segment-wide earthquake chronology, and for each segment-wide earthquake, computed the product of the site PDF probabilities in common time bins. Correlating site PDFs to develop the segment rupture chronology is supported by ~40–60% overlap in site PDFs per earthquake and large displacements per event. The product method incorporates all of the site PDF data, rather than excluding or subjectively weighting the least well constrained data, and because it emphasizes the overlap in the site data, it gives more weight to the narrowest, best-defined PDFs and yields smaller earthquake-timing uncertainties compared to simply computing the mean of the site PDFs. We calculated earthquake recurrence intervals and uncertainties using a Monte Carlo model. Our results indicate that five surface-faulting earthquakes occurred on the Weber segment between ~5.9 and ~0.6 ka, yielding a closed mean recurrence interval of 1.3 ky (four intervals in 5.3 ky), with an estimated 0.6–1.9-ky two-sigma range based on inter-event recurrence. These data clarify the earthquake history of the segment, including the important question of the timing and rupture extent of the most recent earthquake, and have important implications for earthquake-probability analyses, such as the earthquake forecast for the Wasatch Front being developed by the Working Group on Utah Earthquake Probabilities.
Session:Seismic Sources and Parameters
Presenter   Bohnhoff, Marco
Schedule   Wed 4:15 PM / Oral
Room   Ballroom E
Monitoring microseismicity at the Princes Islands segment of the North Anatolian Fault Zone: Recent results from the PIRES network
BOHNHOFF, M., GFZ Potsdam, Potsdam, Germany, bohnhoff@gfz-potsdam.de; EKEN, T., GFZ Potsdam, Potsdam, Germany, wkent@gfz-potsdam.de; BULUT, F., GFZ Potsdam, Potsdam, Germany, bulut@gfz-potsdam.de; CAN, B., Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey, birsenc@boun.edu.tr; AKTAR, M., Kandilli Observatory and Earthquakes Research Institute, Istanbul, Turkey, aktar@boun.edu.tr; DRESEN, G., GFZ Potsdam, Potsdam, Germany, dre@gfz-potsdam.de
The North Anatolian Fault Zone (NAFZ here after) below the Sea of Marmara represents a ‘seismic gap’ where a major earthquake is expected to occur in the near future. This segment of the fault is located between the 1912 Ganos and 1999 Izmit ruptures and is the only NAFZ segment that has not ruptured since 1766. To monitor the microseismic activity at the main fault branch offshore of Istanbul below the Çınarcık Basin (ÇB) a permanent seismic array (PIRES) was installed on the Princes Islands, at a few kilometer distances to the fault. PIRES recordings are combined with data from local permanent stations of the Turkish network (KOERI) and the ARNET seismic network on the Armutlu peninsula in order to get the best available azimuthal control for the target area. As a result we obtain a well-resolved hypocenter catalog of microseismicity allowing us to identify the seismically active structures and their role in local seismotectonic setting. Analysis of data covers the time period 2006-2009 and allowed resolving the existence of two major fault branches beneath the ÇB providing insight into the separation of seismically active from inactive segments along the eastern part of the Marmara seismic gap. Spatiotemporal analysis of microearthquakes based on well-constrained hypocenters is performed to understand the interaction between the sub-segments of the NAFZ along the ÇB. The results show that the seismicity generally tends to cluster slightly off the main fault, probably along splay faults. This probably means that the main fault is locked and the slip is transferred to the secondary structures which might be due to the major NAFZ branch approaching a late stage of the seismic cycle.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Baumann, Cyrill
Schedule   Wed PM / Poster
Room   Ballroom B
Modelling Mw=6.5 Earthquakes Ground Motion in the Valais Area, Switzerland, using Dynamic Rupture Approach.
BAUMANN, C. F. D., Swiss Seismological Service, Zürich, Switzerland, cyrill.baumann@sed.ethz.ch; DALGUER, L. A., Swiss Seismological Service, Zürich, Switzerland, dalguer@tomo.ig.erdw.ethz.ch; BURJANEK, J., Swiss Seismological Service, Zürich, Switzerland, burjanek@sed.ethz.ch; FÄH, D., Swiss Seismological Service, Zürich, Switzerland, donat.faeh@sed.ethz.ch; MICHEL, C., Swiss Seismological Service, Zürich, Switzerland, clotaire.michel@sed.ethz.ch
The Valais area in the Swiss Alps shows the largest seismic hazard in Switzerland. During the past 500 years, the Valais region experienced six earthquakes around magnitudes 6 or larger. Those earthquakes occurred with a periodicity of about 100 years, the most recent one in 1946. The Valais presents rough topography, unstable and steep slopes, deep sediment-filled valleys and wide glacier- and snow-covered areas that potentially increase the seismic risk level due to earthquake-induced phenomena such as strong site- and topographical effects, liquefaction, landslides and snow avalanches. In addition, important critical facilities of Switzerland, such as hydroelectric power plants and chemical plants have been built in the Valais, making the region even more vulnerable to damaging earthquakes. Motivated by this fact, within the framework of the COGEAR project (an interdisciplinary natural hazard project for investigating the hazard induced by earthquakes), we developed a suite of earthquake source physics- based dynamic rupture models consistent with the expected earthquakes in a particular region . Stress distribution prior to earthquakes are assumed to be stochastic with heterogeneous stress consistent, in a statistical sense, with past earthquakes. Evaluation of the current seismic activity and seismotectonics in the area suggests normal fault as potential fault mechanism. Evidences of the existence of a fault are deduced from the spectral signatures of seismic ambient noise recorded during a seismic survey along the expected fault. These seismological observations together with geological evidences and observed instrumental seismicity are used to constraint the fault location, size and mechanism of our model. The ground motion modeled from the simulated earthquakes are adequately treated to assess the level and variability of ground motion for seismic hazard and risk mitigation, particularly to contribute to the evaluation of critical structures.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Graves, Robert
Schedule   Wed 8:30 AM / Oral
Room   Ballroom E
The SCEC Broadband Ground Motion Simulation Platform
SOMERVILLE, P. G., URS Corporation, Los Angeles, CA, paul_somerville@urscorp.com; CALLAGHAN, S., University of Southern California, Los Angeles, CA, scottcal@usc.edu; MAECHLING, P., University of Southern California, Los Angeles, CA, maechlin@usc.edu; GRAVES, R. W., U.S. Geological Survey, Pasadena, CA, rwgraves@usgs.gov; COLLINS, N., URS Corporation, Los Angeles, CA, nancy_collins@urscorp.com; OLSEN, K. B., San Diego State University, San Diego, CA, kbolsen@sciences.sdsu.edu; IMPERATORI, W., Institute of Geophysics, ETH, Zurich, Switzerland, imperatori@tomo.ig.erdw.ethz.ch; JONES, M., UC San Diego, La Jolla, CA, m1jones@ucsd.edu; ARCHULETA, R., UC Santa Barbara, Santa Barbara, CA, ralph@crustal.ucsb.edu; SCHMEDES, J., UC Santa Barbara, Santa Barbara, CA, jasch@umail.ucsb.edu; JORDAN, T.H., University of Southern California, Los Angeles, CA,tjordan@usc.edu
The Southern California Earthquake Center (SCEC) Broadband Ground Motion Simulation Platform is a collaborative software development project involving SCEC researchers, graduate students, and the SCEC Community Modeling Environment. The Platform has been developed by integrating scientific modeling codes into a system capable of computing broadband seismograms using physics-based simulation approaches. The Platform provides the user with the flexibility to select from various alternative approaches for generating the earthquake rupture description, modeling low- and high-frequency wave propagation, and incorporating site effects. Users may calculate broadband seismograms for both historical earthquakes (validation events currently include Northridge, Loma Prieta, and Landers) and user-defined scenario earthquakes. The Platform produces a variety of data products in standardized formats, including broadband seismograms, rupture visualizations, and goodness-of-fit plots. The Platform is open-source software, providing scientists and engineers with visibility into all scientific and supporting codes, and it was implemented using software development best practices that support software accuracy, reliability, and ease of use, including version control, user documentation, acceptance tests, and formal software releases. The Platform has been designed so that a person with no involvement in the development of any of the computer codes is able to perform ground motion simulations without assistance, which is an important step in gaining acceptance of the use of simulated grounds in earthquake engineering research and practice. The PEER NGA-East Project is planning to use the Platform for the validation of simulation methods for the Central and Eastern United States, and the generation of simulations for the construction of ground motion prediction equations for that region.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Dreger, Douglas
Schedule   Wed PM / Poster
Room   Ballroom B
Very Near-Fault Ground Motion Simulation
DREGER, D. S., UC Berkeley, Berkeley, CA, dreger@seismo.berkeley.edu; LARSEN, S., LLNL, Livermore, CA, ; YOO, S. H., UC Berkeley, Berkeley, CA, hoonthhoonth@gmail.com; CHOPRA, A., UC Berkeley, Berkeley, CA, chopra@ce.berkeley.edu
Very near-fault ground motions, distances of less than 100m, are of considerable interest to the Earthquake Engineering community. Bridges and other lifeline structures that either span across faults or are situated on one side, but close by, will be subjected to large dynamic motions and static strain. There are essentially no direct observations in this distance range, saving for the 1966 records of the M6 Parkfield earthquake, and therefore numerical simulation is needed to understand the types of possible motions. While in this near-fault distance range the strain and strain rate will be high leading to likely non-linear processes there is still a need to first document the types of motions possible under elastic assumptions. We will present a new functional form of the seismic moment rate function that is suitable for kinematic simulations of strong ground motion. Finite-difference ground motion simulations assuming elastic, homogeneous structure for hypothetical M6.5 earthquakes with a variety of fault geometry and slip types will be compared. These simulations demonstrate directivity and tectonic rebound, or fling, controlled motions that range from symmetric, anti-symmetric or asymmetric at pairs of stations spanning the modeled fault. For buried faults large static strain (order of 20 cm over 0 to 40 m from a fault with slip of 70 cm) can occur across structures located entirely on one side of a fault. Finally, we will present preliminary results incorporating finite-difference simulations taking into consideration bimaterial structure across the fault, the inclusion of a narrow, low velocity damage zone, and random velocity variations in the surrounding medium to generate a high-frequency scattered wavefield to assess these effects on very-near-fault ground motions.
Session:Geometry effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Presenter   Thompson, Eric
Schedule   Wed 5:30 PM / Oral
Room   Room 204/205
A Classification Scheme for Site Response Complexity
THOMPSON, E. M., Tufts University, Medford, MA, eric.thompson@tufts.edu; BAISE, L. G., Tufts University, Medford, MA, laurie.baise@tufts.edu; TANAKA, Y., Research Center for Urban Safety & Security, Kobe University, Kobe, Japan, ytgeotec@tiger.kobe-u.ac.jp; KAYEN, R., U. S. Geological Survey, Menlo Park, CA, rkayen@usgs.gov
Reliable calibration and validation of constitutive models require many case studies. Ideally, these case studies should sample a realistic range of model input parameters. However, only a few extensively studied downhole arrays are commonly used for calibration and validation of nonlinear models, such as the Large-Scale Seismic Test (LSST) site in Lotung, Taiwan. Thus, there is a critical need to increase the number of sites that are commonly used for nonlinear calibration and validation of dynamic soil constitutive models. Toward this end, we discuss a classification scheme for downhole array sites that can be used to identify those stations that should be used to validate one-dimensional nonlinear constitutive models. For stations where the one-dimensional assumption does not hold, we distinguish between different levels of complexity that must be accounted for in the site response analysis. To validate the classification scheme, we analyze a pair of stations where the proposed taxonomy suggests that the assumption of laterally constant layering is valid at one site and invalid at the other. We test the physical interpretation of this classification by measuring the velocity profile at four locations in the vicinity of each. These data show that the lateral variations of the velocities are substantially larger at the site where the classification scheme suggests that the assumption of laterally constant layers is violated. We also demonstrate that these three-dimensional effects result in significant overestimation of the site response amplifications due to the seismic scattering that results from three-dimensional heterogeneities.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Ebel, John
Schedule   Thu 9:45 AM / Oral
Room   Ballroom C
The Probability of M≥7 Earthquakes in Central and Eastern North America
EBEL, J. E., Weston Observatory/Boston College, Weston, MA, ebel@bc.edu
Several earthquakes of M≥7 have taken place in central and eastern North America during historic time, and they have occurred at a rate greater than that predicted by Gutenberg-Richter recurrence curves for the region. This study tests to see if this enhanced rate of M≥7 earthquakes is a short-term statistical anomaly or whether it is a long-term characteristic of the seismicity of this region. The analysis builds on the paleoseismicity idea that localized clusters of earthquakes in eastern North America delimit aftershock zones of past strong earthquakes. It is assumed that persistent localized clusters of smaller earthquake activity in the central and eastern U.S. (CEUS) are locations where M≥7 earthquakes may have taken place in the past few thousand years. Using the current rates of small earthquakes in each of these clusters, an estimate is made of the time of a possible past M≥7 earthquake at each cluster location. The total number of postulated M≥7 earthquakes in the CEUS during the past 1100 and 2100 years is counted and compared to the number expected from the Gutenberg-Richter recurrence curves computed from the modern seismicity. The results of this analysis indicate that the rate of M≥7 earthquakes in the CEUS over the past couple thousand years has been a factor of 2 to 3 higher than that expected based on the modern seismicity. This suggests that current seismic hazard analyses may underestimate the low probability seismic hazard for the region.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Schmauder, Gretchen
Schedule   Wed PM / Poster
Room   Ballroom B
Evaluating Shallow Shear Wave Velocity Near Quaternary Faults in the Truckee Meadows Basin, Reno, Nevada
SCHMAUDER, G. C., University of Nevada, Reno, Reno, NV, gcschmauder@terracon.com; LOUIE, J. N., University of Nevada, Reno, Reno, NV, louie@seismo.unr.edu; ISLAM, F., University of Nevada, Reno, Reno, NV, fariha_i@hotmail.com; PULLAMMANAPPALLIL, S., Optim, Reno, NV, satish@optimsoftware.com
We evaluate shear wave velocity using the refraction microtremor technique at 20 locations near known and inferred Quaternary faults in the southwestern portion of the Truckee Meadows basin, Nevada. For each refraction microtremor measurement we used a 200-meter-long array of twenty-four 4.5-Hz geophones. We collected the data on a 24-channel Seismic Source DAQlink II 24-bit acquisition system using a 24-second record length with a 2.0-ms sampling interval. Most of the arrays either crossed the fault traces, or aligned parallel with the strikes of the faults. However, we did place several arrays away from the faults to identify local baseline shear-wave velocities. We processed the refraction microtremor data using SeisOpt® ReMi™ version 4.0 (© 2010 Optim) Vspect and Disper modules. Our initial hypothesis was that changes in shear velocity laterally across a fault should be identifiable in the refraction-microtremor results. Faults were located and assessed by R. Frary and others by tying her overlapping P-wave seismic-reflection imaging results (from surveys in 2009 and 2010) to the USGS Qfaults database. Our preliminary results suggest that the data do not support this hypothesis at this location. Lateral and vertical changes in the shear-wave velocities across faults are not observed in the preliminary velocity profiles. The shear-wave velocities, vertically averaged to 30 meters depth (Vs30), range from approximately 300 m/s to approximately 830 m/s, and correlate strongly to local basin stratigraphy. Our results suggest two further hypotheses. The first is that the overlying alluvium is too deep (at 50 to 100 m) and that 200-m-long arrays were not sufficiently sensitive to changes in shear wave velocity below the basin floor of Tertiary volcanics. The second is that the geologic nature of the volcanics and basin sediments (e.g., composition, cementation, etc.) are more important factors and may overshadow the effects that faulting has on shear wave velocity.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Garcia, Daniel
Schedule   Fri AM / Poster
Room   Ballroom B
ShakeMap Atlas 2.0: A Considerable Improvement of the Global Catalog
GARCIA, D., U.S. Geological Survey, Golden, CO, danielgarcia@usgs.gov; MARANO, K. D., U.S. Geological Survey, Golden, CO, kmarano@usgs.gov; HEARNE, M. G., U.S. Geological Survey, Golden, CO, mhearne@usgs.gov; WORDEN, C. B., Synergetics Inc., Fort Collins, CO, cbworden@caltech.edu; LIN, K. W., U.S. Geological Survey, Golden, CO, klin@usgs.gov; WALD, D. J., U.S. Geological Survey, Golden, CO, wald@usgs.gov
The USGS ShakeMap system is a widely used tool for assessing the ground motion during an earthquake in near-real time applications, but also for past events and seismic scenarios. The ShakeMap Atlas (Allen et al., 2008) is a compilation of nearly 5,000 ShakeMaps of global events that comprises the most damaging and potentially damaging earthquakes between 1973 and 2007. The Atlas is an invaluable resource for investigating strong ground-motion near the source, and it is also used for calibrating the USGS Prompt Assessment of Global Earthquakes for Response (PAGER) system.Here we present the second version of the Atlas, which includes as new features the use of: (1) a new version of ShakeMap; (2) an updated source catalog; (3) a refined ground-motion prediction equation (GMPE) selection; and (4) many more intensity and ground-motion data. The new version of ShakeMap (3.5; Worden et al., 2010) treats in a separate way native and converted data when producing each map (MMI, PGA, PGV, and PSA). This is especially important for intensity observations, which are the main data source in the aftermath of most global events. ShakeMap 3.5 also allows for inclusion of intensity prediction equations and makes use of improved mapping techniques and uncertainty estimations. Earthquake global hypocenters have been substituted, when possible, for regional locations and, in some cases, finite source models not included before. The Atlas span has also been extended till 2010. In order to improve the adequacy of the GMPE used by ShakeMap to estimate the ground shaking for a given event where data are not available, we use a new global scheme to discriminate between different types of earthquakes (García et al., 2011). Finally, we have included a large amount of recently available observations from national and regional networks. All these improvements make the new version of the ShakeMap Atlas a greatly improved resource for global hazard analyses and earthquake loss calibration.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Williams, Robert
Schedule   Thu AM / Poster
Room   Ballroom B
Preliminary Results from Seismic Imaging near the Marianna, Arkansas, Sand-Blow Trend
WILLIAMS, R. A., US Geological Survey, Golden, CO, rawilliams@usgs.gov; DADA, O., University of Oklahoma, Norman, OK, Olamide.Dada-1@ou.edu; STEPHENSON, W. J., USGS, Golden, CO, wstephens@usgs.gov; ODUM, J. K., USGS, Golden, CO, odum@usgs.gov; WORLEY, D. M., USGS, Golden, CO, worley@usgs.gov; MCCALLISTER, N. S., USGS, Memphis, TN, nmccallister@usgs.gov
A linear trend of mid-Holocene earthquake-induced sand blows near Marianna, Arkansas, prompted the USGS in June 2010 to look for possible related faults in this area using high-resolution P-wave seismic reflection profiles. The field area is located in east-central Arkansas about 75 km southwest of Memphis, Tennessee, and 80 km south of the southwestern end of the New Madrid seismicity trend. Previous studies of the sand blows indicate that they were produced 5000 to 7000 years ago by large earthquakes of similar magnitude (M7+) to the 1811 and 1812 New Madrid earthquakes. This site adds to a growing list of potentially-active faults discovered in the last 15 years that are within the Mississippi embayment but lie outside the main New Madrid seismicity trend.Two parallel, 5-km-long profiles, with 5- and 10-m geophone and Minivibe source spacing, respectively, were acquired in an east-west direction across the northwest-southeast sand blow trend. Preliminary processing and interpretation of the data reveals several prominent and well known marker reflections imaging the top of the Paleozoic and overlying Cretaceous sections, as well as several coherent reflections within the Tertiary section. In one profile there are two west-up vertical discontinuities in the Paleozoic reflection at about 1100 m depth that are strongly suggestive of steeply dipping reverse faulting. The western-most fault displacement is larger and appears to have recurrent motion with about 40 m of uplift on the Paleozoic reflection and about 20 m of foldeing on Eocene reflections at 400 m depth. The magnitude of these fault and fold displacements are typical of those seen in many reflection profiles that image the Paleozoic and younger section in the Mississippi embayment region. Additional data processing and analysis are needed to clarify whether the apparent faults reach the base of the Quaternary section.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Malagnini, Luca
Schedule   Thu 2:00 PM / Oral
Room   Room 204/205
Breakdown of earthquake self-similarity observed globally at Mw 5.5
MALAGNINI, L., Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, luca.malagnini@ingv.it; NIELSEN, S., Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, ; MAYEDA, K., Weston Geophysical Corporation, Lexington, MA, kmayeda@yahoo.com; MUNAFO', I., Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, irene.munafo@ingv.it; YOO, S. H., University of California Berkeley, Berkeley, CA, ; BOSCHI, E., Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy,
Normal- and shear- stress dynamic conditions acting on fault surfaces at seismogenic depths (7-15 km) can nowadays be reproduced by lab apparatuses. Experiments show that, for both cohesive and non-cohesive rocks, once the slip velocity reaches typical seismic values (~1 m/sec), and the slip goes past a critical distance, the frictional shear stress decreases to a lubricated steady-state value, about 10% of the static fault strength. Our results show that, regardless of fault type and tectonic environment, at 10 km depth the slip generated by an earthquake of Mw 5.5 is enough to completely lubricate the fault. As a consequence, the slip distributions of large crustal earthquakes tend to occur under low dynamic friction, leaving large portions of the energy budgets available for radiation. The opposite is true for small events.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Williams, Robert
Schedule   Thu 8:45 AM / Oral
Room   Room 204/205
The St. Louis Area Earthquake Hazards Mapping Project
WILLIAMS, R. A., USGS, Golden, CO, rawilliams@usgs.gov; CRAMER, C. H., University of Memphis, Memphis, TN, ccramer@memphis.edu; ROGERS, J. D., Missouri University of Science and Technology, Rolla, MO, rogersda@mst.edu; BAUER, R. A., Illinois State Geological Survey, Champaign, IL, bauer@isgs.illinois.edu; CHUNG, J., Missouri University of Science and Technology, Rolla, MO, jc8r4@mst.edu; GAUNT, D. L., Missouri Division of Geology and Land Survey, Rolla, MO, david.gaunt@dnr.mo.gov; HEMPEN, G. L., URS Corporation, St. Louis, MO, hempen69@sbcglobal.net; STECKEL, P. J., Earthquake Insight LLC, Washington, MO, psteckel@charter.net; HOFFMAN, D., Missouri University of Science and Technology, Rolla, MO; WATKINS, C.M., USGS, Rolla, MO; BOYD, O.L., USGS, Memphis, TN; McCALLISTER, N.S., USGS, Memphis, TN
The St. Louis Area Earthquake Hazards Mapping Project is a major urban hazard mapping effort supported by the U.S. Geological Survey (USGS) External Earthquake Hazards Program. The goal of the project is to provide state-of-the-art urban seismic hazard maps for the greater St. Louis area in Missouri and Illinois that can be used in land-use planning, public policy making, and private sector decision making. Urban seismic hazard maps that include the effects of local geology are being prepared. The project includes subsurface geological, geophysical, and geotechnical information to form a three-dimensional soils database. Reference soil profiles were generated from shear-wave velocity (Vs) measurements for the uplands (loess/till) and lowlands (alluvial) portions of the study area. Site amplification ranges (distributions) are then generated by the randomization of the Vs profile, dynamic properties, and appropriate input ground motions and then used to generate probabilistic and scenario ground motion hazard maps. For PGA and 0.2s Sa, the resulting urban hazard maps show increased ground motion hazard in the uplands, which are thinly covered by loess/till, and similar ground motion hazard in the 30-50 m thick alluvium lowlands relative to the 2008 USGS national seismic hazard maps. For 1.0s Sa, the urban seismic hazard maps show a reversed pattern of greater amplification on lowlands soil than upland soils. Liquefaction potential of Quaternary deposits has also been assessed. Holocene alluvial units in river valleys and flood plains are the most susceptible to liquefaction. Because many transportation routes, power and gas transmission lines, population centers, and levee structures exist on the highly susceptible Holocene alluvium, parts of the greater St. Louis area are at significant potential risk from seismically induced liquefaction and related ground deformation.
Session:Assessment of Seismic Hazard from Paleoliquefaction Studies
Presenter   Hylland, Michael
Schedule   Fri PM / Poster
Room   Ballroom B
Paleoseismic Trench Investigation of the West Valley Fault Zone, Salt Lake City, Utah—Preliminary Results
HYLLAND, M. D., Utah Geological Survey, Salt Lake City, UT, mikehylland@utah.gov; DUROSS, C. B., Utah Geological Survey, Salt Lake City, UT, christopherduross@utah.gov; MCDONALD, G. N., Utah Geological Survey, Salt Lake City, UT, gregmcdonald@utah.gov; OLIG, S. S., URS Corporation, Oakland, CA, susan_olig@urscorp.com
The West Valley fault zone (WVFZ), an intrabasin normal-fault system in northern Salt Lake Valley, lies 10 km west of, and is antithetic to, the west-dipping Salt Lake City segment of the Wasatch fault. Both faults have had recurrent Holocene surface-faulting earthquakes, but the seismogenic relation between the two faults is unknown. Few unmodified scarps on undeveloped land and a typically shallow water table have limited previous paleoseismic study of the WVFZ mostly to borehole exploration, and timing and displacement data for individual surface-faulting earthquakes are sparse and poorly constrained. Low groundwater levels associated with Great Salt Lake levels near the historic lowstand allowed us to excavate trenches to a maximum depth of 3 m across a 0.25-m-high eastern scarp and 1-m-high western scarp at the north end of the WVFZ. Our trench across the eastern scarp exposed warping (0.5±0.1 m vert. offset) of late Pleistocene Lake Bonneville strata and overlying subaerial deposits, probably the result of a single late Holocene earthquake. Two parallel trenches across the western scarp exposed structural and stratigraphic evidence for four surface-faulting earthquakes occurring after the 18 ka highstand of Lake Bonneville. Fault-zone deformation includes stratal warping associated with the oldest earthquake (sub-lacustrine) and shear associated with the three subsequent faulting events. Associated deposits of scarp-derived colluvium are preserved only for the two most recent events. Measurements of correlative strata across the fault zone indicate 0.9±0.2 m of vertical offset since ~10(?) ka and 1.9±0.2 m since ~20(?) ka (av. 0.5 m per event). Constraints on earthquake timing will come from C-14 and luminescence dating, as well as ostracode biostratigraphy. The WVFZ surface-faulting chronology will be compared with that of the northern Salt Lake City segment, which was trenched in May 2010, to provide insight into the seismogenic relation of the two faults.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Ellsworth, William
Schedule   Thu 3:45 PM / Oral
Room   Room 204/205
No Sign of a Breakdown in the Magnitude Invariance of Stress Drop at SAFOD
ELLSWORTH, W. L., U. S. Geological Survey, Menlo Park, CA, ellsworth@usgs.gov; IMANISHI, K., Geological Suvrvey of Japan AIST, Tsukuba, Japan, imani@ni.aist.go.jp
Near-source, high-sample-rate recordings of earthquakes in the SAFOD main hole at short hypocentral distances make it possible to study source parameters to smaller magnitude that is possible with data from instruments in shallow boreholes or on the surface. Only a small fraction (<1%) of the fault surface near SAFOD produces earthquakes. The earthquakes that do occur are predominately located within clusters of repeating events, suggesting that are velocity-weakening patches embedded within an otherwise creeping fault. Source parameters for earthquakes within 3 km of a 15-Hz 3-component geophone deployed within the fault zone at depths between 2550 and 2660 m were determined by the Multi-Window Spectral Ratio (MWSR) method (Imanishi and Ellsworth, doi:10.1029/170GM10). Spectral ratios are formed pair wise for events in each cluster. The key step in the method is to stack the ratios calculated in multiple overlapping windows taken along the record starting with the direct waves. For M≥-1, the calculated stress drops range between 0.1 and 100 MPa, spanning the same range as global compilations made at much larger magnitude. This indicates that constant-stress-drop scaling at SAFOD extends at least to M -1. While events with M<-1 are observed, their corner frequencies generally lie above the Nyquist frequency of the data (500 Hz to 2000 Hz, depending on recording time period). The largest stress drops for SAFOD events approach the laboratory-derived frictional strength of crustal rocks, implying a fault surface that locally juxtaposes crustal rocks with typical strengths. We also notice that the stress drops for any given cluster are the same within one order of magnitude, while mean stress drops across all clusters vary by about three orders of magnitude. This spatial variability must reflect different material properties and/or source processes along the fault.
Session:Ground Motion Scaling and Selection
Presenter   Malekmohammadi, Mojtaba
Schedule   Fri 11:00 AM / Oral
Room   Room 204/205
Ground Motion Selection and Scaling to Obtain Suites of Ground Motions Compatible with the Uniform Hazard Spectra for Rock Site Conditions
MALEKMOHAMMADI, M., The University of Memphis, Memphis, TN, mmlkmhmm@memphis.edu; PEZESHK, S., The University of Memphis, Memphis, TN, spezeshk@memphis.edu
Selection of ground motions is a key step in the time history analysis of structures, and yet there are limited procedures and recommendations available in the literature on details of the selection process. In the time-history analysis, we need to select ground motions that match an appropriate uniform hazard response spectrum (UHRS) obtained from a probabilistic seismic hazard analysis (PSHA). In this study, we propose a new step-by-step method to select a set of ground motions from different databases which takes into account a site-specific PSHA and the associated uncertainties. New Madrid hypothetical faults defined by the 2008 USGS were used as the hazard source along with two different ground motion prediction models (Tavakoli and Pezeshk, 2005; Campbell, 2003) in performing PSHA for a sample site in central US. Following a logic tree approach, we first determine a mean and standard deviation (± HC) of the hazard at different spectral accelerations for a return period of 2,475 years. Using this information, we then determine the UHRS as well as the extreme limits of spectral amplitude associated with ± HC. Spectral accelerations associated with ± HC about the mean hazard curve are used as the extreme limits to represent the epistemic uncertainties in a given site. In this study, we made simplifying assumptions of using equal weight for all branches of the logic tree. A Monte Carlo procedure is used to produce 1,000 sets of 7 response spectra. Out of these 1,000 sets of response spectra, we select a set that has the closest mean and falls within ± HC. Then, as seed earthquakes, we select ground motions from the database of recorded ground motions, records produced using a point-source stochastic procedure, and records generated using a stochastic finite fault model. Final results from each category are then compared with each other and appropriate suggestions are given for the selection of the ground motions from each database.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   McDuffie, Stephen
Schedule   Thu 1:30 PM / Oral
Room   Ballroom E
The Central and Eastern United States Seismic Source Characterization (CEUS SSC) Project for Nuclear Facilities
MCDUFFIE, S. M., U.S. Department of Energy (DOE), Richland, WA, stephen.mcduffie@rl.doe.gov; COPPERSMITH, K. J., Coppersmith Consulting, Inc., Walnut Creek, CA, kcoppersmith@earthlink.net; STIREWALT, G. L., U.S. Nuclear Regulatory Commission (NRC), Washington, DC, Gerry.Stirewalt@nrc.gov
The CEUS SSC project will provide a regional seismic source model for the region east of the Rocky Mountains for performing probabilistic seismic hazard analyses at proposed nuclear facility sites. This regional source model is being developed using Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 guidelines under sponsorship of the commercial nuclear industry, the DOE, and the NRC. The SSHAC methodology aims to represent the center, body, and range of technically defensible interpretations and permits the incorporation of existing seismic source models and the development of new assessment methods and models. To apply the methodology, a Technical Integration (TI) Team first identified available hazard-relevant data, source models, and assessment methods based on input from technical resource experts. These facets were evaluated by the TI Team to determine quality and applicability through interactions with their proponents at two workshops, during which a proponent’s views were subjected to technical challenge. Seismic hazard influences were directly addressed in a third workshop to focus on the most relevant issues, and the technical bases for the final weights assigned to different models and parameters were justified and documented.The CEUS SSC project is developing the following materials to support the regional seismic source model: a comprehensive catalog of historical and instrumented seismicity with a uniform moment magnitude assessment for all events; a comprehensive database of currently available data; and data evaluation tables which document the TI Team’s review of salient information. The project is also implementing innovative approaches to spatial smoothing of observed seismicity and modeling of maximum magnitudes, and incorporating available paleoseismic data to characterize size and recurrence of repeated large-magnitude earthquake sources. The final regional seismic source model and report will be available in mid-2011.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Seligson, Hope
Schedule   Fri 3:45 PM / Oral
Room   Ballroom D
Lessons Learned Improving Building Inventory Databases in California Using Assessor’s Data
SELIGSON, H. A., MMI Engineering, Huntington Beach, CA, hseligson@mmiengineering.com
Over the last decade, Assessor’s data for a number of Counties in California have been utilized to build improved inventory databases for HAZUS® (HAZards U.S.), the GIS-based nationally-applicable multi-hazard loss estimation software developed by the Federal Emergency Management Agency (FEMA). Counties that have been the subject of database development projects include San Francisco, Los Angeles, San Luis Obispo, Orange, Riverside, and San Bernardino. A variety of challenges exist relative to the use of California Assessor’s data, including lack of data on non-taxable structures, limited inclusion of mobile home data, non-uniform valuation basis, and the required aggregation of condominium parcel records. With each subsequent database developed, new technology applications are explored, additional lessons are learned and existing development strategies are fine-tuned. This paper provides a summary of recommended approaches and lessons learned over time.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Odum, Jack
Schedule   Wed PM / Poster
Room   Ballroom B
Shallow 3.5 km Long, Shear-wave Velocity Profile in Reno, Nevada Derived from Ambient Noise Analysis of Uncorrelated P-wave Minivib Data
ODUM, J. K., U.S. Geological Survey, Golden, CO, odum@usgs.gov; STEPHENSON, W. J., U.S. Geological Survey, Golden, CO, wstephens@usgs.gov; FRARY, R. N., Univ. of Nevada, Reno, NV, rfrary0615@gmail.com; SCHMAUDER, G. C., Seismological Lab. Univ. of Nevada, Reno, NV, gcschmauder@terracon.com; LOUIE, J. N., Seismological Lab, Univ. of Nevada, Reno, NV, louie@seismo.unr.edu
We characterize S-wave velocities (Vs) to 100 m depth on the southwestern side of the Truckee Meadows basin, Nevada by analyzing ambient noise recorded in uncorrelated minivib (vibroseis) data. These data were originally collected as part of a collaborative (USGS, University of Nevada Reno, and nees@UTexas) high-resolution P-wave seismic reflection imaging investigation for mapping active faults in the Reno area. By processing these data using the refraction microtremor (ReMi) technique, we develop an approximately 3.5 km long two-dimensional Vs structure profile across the faulted southwestern portion of the Truckee Meadows basin. Using the uncorrelated raw field data, we process 20 records from ten adjacent source locations, with 144 channels each to obtain frequency-slowness images for the ReMi analysis. This results in roughly 720 m aperture for analyzing longer wavelengths. After adjusting the one-dimensional S-velocity-depth models obtained from ReMi analysis to the elevation at the mid-points of the array, we interpret three laterally semi-continuous layers across the more basinward length of the profile that merge into two layers on the western (hillside) portion of the profile. Average Vs of the basinward layers are 270, 340 and 550 m/s (to 100m depth). Layer boundaries tend to follow the structural configuration imaged by the P-wave reflection profile and show elevation changes and deformation in areas where faults are interpreted on the seismic-reflection profile. A continuous Vs30 (average Vs to 30 m depth) profile shows higher (350 to 400 m/s) values on the western third of the line and lower values (315 to 350 m/s) in the basinward region. Corroborating ReMi data taken on and off the main transect in March 2010, using N-S and E-W array orientations, are compared with nearby models derived from the analysis of the raw uncorrelated P-wave reflection profile data (see other Manzanita profile posters for details).
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Gammans, Christine
Schedule   Thu PM / Poster
Room   Ballroom B
Is the Relationship Between Modern Seismicity and Strain Fields Well Behaved in the Plate Interior?
GAMMANS, C. N., Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, ; NEWMAN, A. V., Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, anewman@gatech.edu
Our understanding of earthquake behavior and recurrence in plate interiors is limited. This is, in major part, because we cannot often observe the low-level deformation that is loading faults, leading to a lack of well-constrained models that describe earthquake behavior. Regardless, earthquakes remain a threat to populations and structures in such environments making it necessary to estimate earthquake potential with limited information. In this study, we attempt to evaluate whether a general characteristic relationship exists between the frequency-magnitude relationship of ongoing moderate earthquakes and microseismicity and low-level plate interior deformation. We evaluate ongoing activity in the Eastern US where no consistent strain field has yet been detected, and the more seismically active and coherently deforming Chinese interior. We specifically evaluate whether the activity parameter increases regularly with plate interior strain rates. To develop a robust and testable strain field for these regions, kriging is used to interpolate the velocities between residual GPS velocity in each region determined after corrections are made for stable plate motion. The new regularly spaced velocities are used to determine the approximate maximum shear strain for individual regions, which are then compared to observed activity rates to observe correlation and determine the robustness of the relationship. Such a relationship if well resolved has significant implications for evaluating seismic hazards in intraplate environments.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Mulargia, Francesco
Schedule   Wed 4:30 PM / Oral
Room   Ballroom D
Elastic and anelastic seismic passive imaging
MULARGIA, F., Dipartimento di Fisica, Università di Bologna, Bologna, Italy, francesco.mulargia@unibo.it; CASTELLARO, S., Dipartimento di Fisica, Università di Bologna, Bologna, Italy, silvia.castellaro@unibo.it
The physical property at the basis of passive acoustic imaging is that, taken any two points, one of them can be seen as the source of the waves and the other as the recording station (Weaver, J. Acoust. Soc. Am., 71, 1608, 1982; Snieder, Phys. Rev. E, 69, 046610, 2004). This property has been shown to hold also for non-diffuse wavefields under mild constraints that generally apply to the seismic noise wavefield (Mulargia & Castellaro, Phys. Rev. Lett., 100, 218501-1, 2008; J. Acoust. Soc. Am., 127, 1391, 2010). While somehow empirically embedded in the SPAC (and in its epigones ESAC, MSPAC, etc.) and ReMi techniques, of which it appears to constitute the physical root, this property has never been fully exploited. We show that its statistical features allow to combine the information efficiency of the latter techniques with the beam-forming capability of the f-k technique. The practical application to seismic surveying together with the use of the statistical mode as a location estimator appears to allow passive simultaneous measures of 1) the local phase and group velocities, 2) the local Q value as a function of frequency and 3) the azimuth of the instantaneous Huygens noise sources, at the same time conveniently disposing of the need of a) fitting Bessel functions, b) using complex multi-station array layouts c) adopting recording times longer than 1000 seconds.
Session:Seismotectonics and Hazards of Active Margins in the Circum-Caribbean Sea and Eastern Pacific Ocean
Presenter   Doser, Diane
Schedule   Wed 9:45 AM / Oral
Room   Ballroom D
Revisiting the 1979 St. Elias, Alaska, Aftershock Sequence
DOSER, D. I., University of Texas at El Paso, El Paso, TX, doser@utep.edu
The 1979 Mw=7.3 St. Elias, Alaska, earthquake occurred in a portion of southeastern Alaska where the eastern portion of the Yakutat microplate and Pacific plate begin to subduct beneath North America. The most recent studies of the St. Elias aftershock sequence were completed nearly 20 years ago, prior to collection and re-interpretation of seismic reflection and potential field data that better define the complex regional geometry of the subduction zone. Previous studies also concentrated on the first 2 months of the aftershock sequence, although seismicity continued to propagate southward from the initial rupture zone for over 3 years. I have relocated seismicity occurring within the St. Elias region from 1971 to 2005 to examine space-time seismicity patterns, possible static stress triggering, and the sequence’s relation to recent studies of crustal structure. One of the greatest clusters of aftershocks, including two of the Mw>5.5 aftershocks occurring within the first year of the sequence, occurred at the southern end of the mainshock rupture between the two rupture planes of the mainshock where Coulomb failure stress exceeded 6 MPa. Many aftershocks trend north-south across mapped surface faults of the Chugach-St. Elias fault zone (C-SEFZ), suggesting linkages of the faults with depth along a detachment surface that may represent the top of the Yakutat microplate. Deeper (10-20 km) aftershocks of the sequence appear to wrap around the edges of a gravity high that occurs at the intersection of the Pamplona fault zone with the C-SEFZ.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Frankel, Arthur
Schedule   Thu 9:30 AM / Oral
Room   Room 204/205
Urban Seismic Hazard Maps for Seattle, Washington, Based on 3D Ground-Motion Simulations
FRANKEL, A., U.S. Geological Survey, Seattle, WA, afrankel@usgs.gov; STEPHENSON, W., U.S. Geological Survey, Golden, CO, wstephens@usgs.gov; CARVER, D., U.S. Geological Survey, Golden, CO, carver@usgs.gov; ODUM, J., U.S. Geological Survey, Golden, CO, odum@usgs.gov; WILLIAMS, R., U.S. Geological Survey, Golden, CO, rawilliams@usgs.gov; RHEA, S., U.S. Geological Survey, Golden, CO, rhea@usgs.gov
We have constructed probabilistic seismic hazard maps for Seattle for 1 Hz spectral acceleration using over five hundred finite-difference simulations with a 3D velocity model. The maps incorporate the fault recurrence parameters applied in the National Seismic Hazard Maps. The 3D velocity model was validated using recorded and synthetic seismograms for four earthquakes. The hazard maps include the amplification in the Seattle basin from basin surface waves and basin-edge focusing. The maps also incorporate the nonlinear amplification at soft-soil sites (fill and Holocene alluvium), by using estimates of the 30m averaged shear-wave velocity (Vs30) and empirical amplification factors. Finite-fault simulations were done for M6.6-7.0 earthquakes on the Seattle fault zone and M7 earthquakes on the Southern Whidbey Island fault. Simulations for point sources at different locations of the Cascadia subduction zone were used to estimate the amplification expected for great Cascadia earthquakes. Point-source simulations were conducted for shallow and deep earthquakes at various azimuths to determine the basin amplification expected for background earthquakes. The resulting hazard maps show that the highest 1 Hz hazard occurs at soft-soil sites within the Seattle basin, with the next highest hazard at stiff-soil sites in the basin and soft-soil sites outside the basin. For 2% probability of exceedance in 50 years, we find that the 1 Hz probabilistic ground motions for sites in the Seattle basin are about twice those derived from the NEHRP amplification factors based on the average Vs30. This difference is caused by the amplification of basin surface waves and by forward rupture directivity of earthquakes on the Seattle fault.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Castellaro, Silvia
Schedule   Wed 5:15 PM / Oral
Room   Ballroom D
A statistical model of the Earth's low seismic noise and its implication for seismic passive surveys
CASTELLARO, S., Dipartimento di Fisica, Università di Bologna, Bologna, Italy, ; MULARGIA, F., Dipartimento di Fisica, Università di Bologna, Bologna, Italy,
An accurate modeling of the background seismic noise is important to modern seismology in two respects: 1) the identification of the best sites for permanent seismic stations, which see noise as a nuisance; 2) the definition of the excitation function for all passive seismological studies, which use seismic noise as a quasi-diffuse wave source. The presently most popular Earth low noise model (NLNM) was compiled by Peterson in 1993 and is based on the ‘minimum’ noise level recorded at 75 IRIS stations. This model, by taking the envelope of the lowest values, relies on no statistical analysis and, as stated by the same author, cannot be considered reliable at frequencies above 2.5 Hz. Subsequent works slightly extended the frequency range and considered the general features of noise, but still within a similar empirical approach. We have analyzed statistically the low limit of the seismic noise through a Singpurwalla double log probability density function resulting in a Gumbel type I extreme value distribution. Using the MedNet very broadband station data with one year (2008) recordings allows us to define quantitatively the distribution parameters over the 0.005 - 20 Hz frequency range for both the vertical and horizontal components, which in some ranges result noisier than the previous models. We will discuss some implications of this finding for passive seismic surveys.
Session:Combining Geodetic and Seismic Measurements
Presenter   Hodgkinson, Kathleen
Schedule   Fri PM / Poster
Room   Ballroom B
PBO Borehole Strainmeter Response in the Tidal and Seismic Frequency Bands
HODGKINSON, K., UNAVCO, Boulder, CO, ; MENCIN, D., UNAVCO, Boulder, CO, ; BORSA, A., UNAVCO, Boulder, CO, ; GALLAHER, W., UNAVCO, Boulder, CO, ; GOTTLIEB, W., UNAVCO, Boulder, CO, ; HENDERSON, B., UNAVCO, Boulder, CO, ; JOHNSON, W., UNAVCO, Boulder, CO, ; VANBOSKIRK, L., UNAVCO, Boulder, CO, ; JACKSON, M., UNAVCO
The Plate Boundary Observatory (PBO) includes 75 Gladwin Tensor Strainmeters installed at depths of up to 250 m in cased boreholes. PBO boreholes are multi-instrumented installations with strainmeters, seismometers, barometers and rainfall gauges at all sites. Several also include accelerometers, tiltmeters and co-located GPS. PBO strainmeters have repeatedly recorded aseismic creep in Parkfield and strain transients associated with Cascadia episodic tremor and slip events in the Pacific Northwest. While tensor strainmeters installed in the United States before PBO were almost all low frequency instruments with sample intervals greater than five minutes, PBO strainmeters record at 20 samples per second. The performance of tensor strainmeters at higher frequencies where it is hoped the operating range of seismometers and strainmeters overlap, is a relatively unexplored area. PBO strainmeters record horizontal strain changes along four gauges oriented at different azimuths. Typically the strain-calibration matrix used to combine the 4 gauge measurements into areal and shear strain is based on a comparison of the observed and theoretically predicted tidal signal, e.g., Roeloffs, 2010 and Hart et al., 1996. In this presentation we examine the self-consistency of the strainmeters at higher frequencies and compare this with the degree of self-consistency found in the shear strain M2 and O1 tidal bands.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Begnaud, Michael
Schedule   Wed AM / Poster
Room   Ballroom B
Incorporating Anisotropic Variations in the RSTT Model for the Upper Mantle of Eurasia
BEGNAUD, M. L., Los Alamos National Laboratory, Los Alamos, NM, mbegnaud@lanl.gov; MYERS, S. C., Lawrence Livermore National Laboratory, Livermore, CA, myers30@llnl.gov; BALLARD, S., Sandia National Laboratories, Albuquerque, NM, sballar@sandia.gov; PHILLIPS, W. S., Los Alamos National Laboratory, Los Alamos, NM, wsp@lanl.gov; PASYANOS, M. E., Lawrence Livermore National Laboratory, Livermore, CA, pasyanos1@llnl.gov; ROWE, C. A., Los Alamos National Laboratory, Los Alamos, NM, char@lanl.gov; RAMIREZ, A. L., Lawrence Livermore National Laboratory, Livermore, CA, ramirez3@llnl.gov
Various researchers have modeled upper mantle velocity variations using Pn and Sn travel times. Phillips et al. (2007) and Myers et al. (2010) also included solving for 2D Pn gradient to the standard slowness solution. The Regional Seismic Travel Time (RSTT) model (Myers et al., 2010) is a 2D upper mantle velocity model that incorporates the effect of upper mantle gradient on arrival times. In Eurasia, high gradients appear to be associated with stable and convergent zones, low gradients with extensional zones. Recently, Pei et al. (2007) did a Pn and Sn seismic tomography study in China, also solving for velocity and Pn anisotropy.We inverted travel time data in Eurasia to solve for anisotropy in addition to the upper mantle slowness and gradient of the RSTT model. Using the Bondár et al. (2004) ground truth (GT) criteria as well as a priori knowledge, we have identified ~15,000 GT25 or better events available for tomography in the region. This data set includes ~4300 stations resulting in ~600,000 Pn and ~107,000 Sn arrivals. Summary rays are produced in order to reduce ray redundancy, resulting in a final set of ~162,000 Pn and ~49,000 Sn arrivals.Initial results suggest that Sn velocity and anisotropy variations are consistent with Pn variations and tectonic activity. Solving for anisotropy tends to remove some of the high frequency patterns in the velocity, particularly in Tibet. In addition to identifying anisotropy traits, we will also analyze whether incorporating anisotropy reduces overall residuals significantly enough to suggest its addition to seismic location algorithms.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Frankel, Arthur
Schedule   Thu 3:30 PM / Oral
Room   Ballroom E
Seismic Hazard Maps for Haiti
FRANKEL, A., U.S. Geological Survey, Seattle, WA, afrankel@usgs.gov; HARMSEN, S., U.S. Geological Survey, Golden, CO, harmsen@usgs.gov; MUELLER, C., U.S. Geological Survey, Golden, CO, cmueller@usgs.gov; CALAIS, E., Purdue University, West Lafayette, IN, ecalais@purdue.edu; HAASE, J., Purdue University, West Lafayette, IN, jhaase@purdue.edu
We have produced probabilistic seismic hazard maps for Haiti that include the hazard from the major crustal faults, subduction zones, and background earthquakes. These maps are intended to form the scientific basis for building codes for the rebuilding effort following the January 2010 M7.0 earthquake. The hazard from the Enriquillo, Septentrional, and Matheux-Neiba fault zones was estimated using fault slip rates determined from GPS measurements. The rate of M≥6.5 earthquakes derived from the fault recurrence models is consistent with the historic rate of earthquakes inferred to be located on the Enriquillo and Septentrional faults. The hazard from the subduction zones along the northern and southeastern coasts of Hispaniola was calculated from slip rates derived from GPS data and from the relative plate motion. Spatially-smoothed seismicity was used to characterize the hazard from background shallow earthquakes not on the faults considered explicitly and from deep earthquakes. Hazard maps were made for a firm-rock site condition and for a grid of shear-wave velocity averaged over the top 30 m (Vs30) estimated from the topographic slope. The hazard maps for firm-rock sites depict peak ground acceleration and response spectral accelerations at 0.2, 0.5, 1.0 and 2.0 sec periods. The resulting maps show substantial seismic hazard throughout Haiti, with the highest hazard in Haiti along the Enriquillo and Septentrional faults and the western end of the Muertos Trough. The Matheux-Neiba fault exhibits high hazard in the 2% probability of exceedance in 50 year maps, although its inferred slip rate is poorly constrained and likely represents an upper limit. More work needs to be done to improve slip-rate determinations for the major faults, identify and characterize other active faults, and better quantify seismic-wave propagation and site amplification.
Session:Combining Geodetic and Seismic Measurements
Presenter   Langston, Charles
Schedule   Fri PM / Poster
Room   Ballroom B
Estimating Spatial Displacement Gradients Using Seismic Data
GRANT, E., CERI, University of Memphis, Memphis, TN, egrant005@gmail.com; LANGSTON, C. A., CERI, University of Memphis, Memphis, TN, clangstn@memphis.edu
We present a new technique for estimating spatial displacement gradients at arbitrary locations within both regularly- and irregularly-spaced, two-dimensional (2D) seismic arrays. The spatial displacement gradients are estimated through an interpolation technique based on the assumption that seismic waves travel across the array according to plane-wave propagation. This technique considers the seismic displacements recorded at locations within a 2D array in addition to the derived spatial displacement gradients, at those same locations, using spatial gradient analysis (or wave gradiometry) in 2D. The seismic displacement and spatial displacement gradient information are used together to determine the best-fit polynomial that describes the seismic displacements and spatial displacement gradients across an array in the radial propagation direction. Unlike a previous technique, which assumed that the spatial displacement gradient was the result of uniform strain and/or a rigid-body rotation, this technique can be used in a variety of situations. The conditions for using this technique require that plane-wave propagation is maintained, the wavelength of the seismic wave is large enough to avoid spatial aliasing across the array, and approximate values for both the apparent propagation velocity and direction are known (or can be derived). We present several examples using both synthetic and real seismic data collected by the Anza Seismic Network in southern California to compare the techniques. The results indicate that the estimates of the spatial displacement gradients are improved when using this new technique in situations where strain is not uniform across either regularly- or irregularly-spaced 2D seismic arrays.
Session:Combining Geodetic and Seismic Measurements
Presenter   Langston, Charles
Schedule   Fri 8:45 AM / Oral
Room   Ballroom E
Calibrating Gladwin Tensor Strain-Meter (GTSM) Instruments Using Seismic Data
GRANT, E., CERI, University of Memphis, Memphis, TN, egrant005@gmail.com; LANGSTON, C. A., CERI, University of Memphis, Memphis, TN, clangstn@memphis.edu
Teleseismic data collected by the southern California Anza seismic network have been used for calibrating nearby borehole GTSM instruments of the Plate Boundary Observatory (PBO). We find reasonable agreement between the calibration coefficients derived here using seismic data and the coupling coefficients derived in other studies using theoretical calculations of earth tides. This study investigates whether the coupling coefficients necessary to calibrate the borehole instrument have changed since each station has been installed. We find that the coefficients necessary for calibrating data collected over the course of 2 years are remarkably stable. During the course of calibration, we discovered that some stations had misalignment errors approaching 50 degrees. This study provides an overview of the process necessary to compute the calibration coefficients that linearly relate the raw instrument gauge strains, recorded by borehole GTSM instruments, to the reference formation strains derived from seismic data. The calibration method implemented here is based on the method developed in Hart et al. [1996]. We also discuss two general methods – a multi-station seismic approach and a single-station seismic approach – for deriving the coupling coefficients necessary for GTSM calibration, including error analysis. The results of this study suggest that it should be possible to calibrate the remaining GTSM instruments inside the PBO network if a permanent/temporary array of broadband seismic instruments or a single, co-located broadband seismic instrument is available.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Kieling, Katrin
Schedule   Wed 9:15 AM / Oral
Room   Ballroom E
Estimation of Broadband Ground Shaking from Rapidly Accessible Parameters
KIELING, K., GFZ German Research Centre for Geosciences, Potsdam, Germany, katrin.kieling@gfz-potsdam.de; HAINZL, S., GFZ German Research Centre for Geosciences, Potsdam, Germany, sebastian.hainzl@gz-potsdam.de; WANG, R., GFZ German Research Centre for Geosciences, Potsdam, Germany, rongjiang.wang@gfz-potsdam.de
The rapid simulation of strong ground motion associated with large earthquakes is a key technique for seismic emergency management. We provide a simulation procedure which is able to estimate realistic high-frequency ground motion on the basis of source parameters which are accessible in near-real-time such as hypocentre location, energy magnitude Me, fault mechanism, rupture length and in best cases slip models inferred from teleseimic or geodesic data. Based on these data a finite fault model is assumed and a source-time-function (STF) is attributed to each patch of the fault according to the slip on this patch. High frequencies are introduced by scaling the rise-time in such a way that the total energy magnitude is reproduced. Full solutions for the whole frequency rangeare obtained by convolving the STF of each patch with the corresponding Green’s functions which may be calculated prior to the earthquake.The simulation is applied to the 2008 Wenchuan earthquake (Mw=7.9,Me=8.2). We compare our prediction to the strong ground motion measurements such as peak ground acceleration (PGA). A baseline correction of accelerometer measurements enables us to compare modelled peak ground velocity (PGV) to measurements, too.Additionally we introduce stochastic source characteristics by perturbing the slip distribution as well as the rupture velocity. This leads to a better reproduction of the complex characteristics of ground motion at high frequencies and to a quantification of the uncertainties. Results of the simulation including stochastic perturbations are also compared to the Wenchuan earthquake and to values from empirical ground motion prediction equations.
Session:The Seismo-Acoustic Wavefield
Presenter   Walker, Kris
Schedule   Fri 4:45 PM / Oral
Room   Ballroom C
Studies of Infrasonic Sources and Propagation Using USArray
WALKER, K. T., Institute of Geophysics and Planetary Physics, Scripps, UCSD, La Jolla, CA, walker@ucsd.edu; HEDLIN, M. A. H., Institute of Geophysics and Planetary Physics, Scripps, UCSD, , mhedlin@ucsd.edu; DE GROOT-HEDLIN, C. D., Institute of Geophysics and Planetary Physics, Scripps, UCSD, , chedlin@ucsd.edu
The acoustic atmospheric velocity structure is short-lived and varies at spatial scales much smaller than the average distance of 2,200 km between globally infrasonic arrays. Although this station density is adequate for locating 1 kT atmospheric explosions, it is not ideal for other specific tasks including validating new high-resolution atmospheric velocity models, testing propagation effects due to internal gravity waves, and investigating the nature of shadow zones, also called “zones of silence.” Relatively large infrasonic signals can be observed on seismic channels due to coupling at the Earth's surface. Several recent studies have shown that relatively dense seismic networks fill in the gaps between infrasonic arrays, providing a much denser spatial sampling of the infrasonic wavefields and resulting in a clearer picture of infrasonic propagation. Exploiting the acoustic-to-seismic coupled signals recorded by the USArray, we present our analysis of locating infrasonic sources in the western U.S. by reverse time migrating seismic envelope data. Hundreds of events are detected annually, many of which are registered by the entire USArray (>1500 km). We also present our analysis of infrasound created by a series of rocket motor detonations that occurred at the UTTR facility in Utah in 2007 to assess the utility of G2S mesoscale models and methods to synthesize infrasonic propagation. We model the travel times of the branches using a ray-based approach and the complete wavefield using a FDTD algorithm. Although both approaches predict the travel times to within several seconds, only about 40% of signals are predicted using rays largely due to penetration of sound into shadow zones. FDTD predicts some sound penetration into the shadow zone, but the observed shadow zones, as defined by the seismic data, have considerably narrower spatial extent than either method predicts, perhaps due to un-modeled small-scale structure in the atmosphere.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Al-Qadhi, Okba
Schedule   Thu 11:30 AM / Oral
Room   Ballroom C
Geophysical Investigation of Earthquake-Induced Liquefaction Features, East Central Arkansas
AL-QADHI, O. R., University of Arkansas at Little Rock, Little Rock, AR, oralkadi@ualr.edu; MAHDI, H., University of Arkansas at Little Rock, Little Rock, AR, ; AL-SHUKRI, H. J., University of Arkansas at Little Rock, Little Rock, AR, hjalshukri@ualr.edu; TUTTLE, M., M. Tuttle & Associates, Georgetown, ME, mptuttle@earthlink.net
Sand blows and related feeder dikes preserved in the geological record attest to the occurrence of large earthquakes in the past. Such features initially identified on satellite images and confirmed during field investigations have been found in east-central Arkansas, an area not previously known to have experienced major earthquakes. Sand blows and feeder dikes were mapped using ground penetrating radar (GPR) and capacitively coupled resistivity (CCR) techniques. GPR and CCR surveys were co-located along profiles tens of meters in length to independently verify the location of liquefaction features. This implementation allows 3-D imaging of liquefaction features and related ground subsidence and tracking of a northwest-southeast oriented zone of ground failure for 4 km. Both techniques were instrumental in locating feeder dikes of sand blows and visualizing the contact between sand blows and the buried paleosurfaces. The most prominent anomalies in both GPR and resistivity data correlate with the breach of the silt loam layer indicative of sand dikes. In some cases, resistivity was superior to GPR for imaging liquefaction features, especially when the sediment was wet. Due to the deeper penetration of electric current, the resistivity method can reveal deeper information than the GPR technique. In addition, CCR is better at identifying the lateral limits of sand blows than GPR. On the other hand, GPR was able to precisely locate the feeder dikes, which is an essential step for citing trenches for paleoseismic study of the liquefaction features. This study advances the use of geophysical techniques that was pioneered by many investigators through the implementation of 3-D imaging which allows for quantification of severity of ground failure and of the size of the sand blows.
Session:Guide to Sustainable Seismographic Networks
Presenter   Busby, Robert
Schedule   Fri 11:00 AM / Oral
Room   Ballroom C
Developing a Model for Seismographic Network Installation, Training and Reporting: An Example of Cooperative Action in Chile
BUSBY, R. W., Incorporated Research Institutions for Seismology (IRIS), Washington DCUSA, busby@iris.edu; SIMPSON, D. W., Incorporated Research Institutions for Seismology (IRIS), Washington DCUSA, simpson@iris.edu; BARRIENTOS, S., University of Chile, Santiago, Chile, sbarrien@dgf.uchile.cl; EARLE, P. S., USGS National Earthquake Information Center, Golden, CO, pearle@usgs.gov
Augmenting the new Chilean National Seismic Network, IRIS and the University of Chile are collaborating to establish ten "Global Reporting Geophysical Observatories for Chile" (GRGOC). This will create a national backbone of high quality permanent stations (with broadband, strong motion, infrasound, and meteorological sensors) and enhance global coverage in the southern hemisphere. IRIS received support from the National Science Foundation to acquire and install ten stations, based on EarthScope Transportable Array station design. Demonstration and training in the techniques developed during deployment of USArray are expected to greatly facilitate the execution of new station deployment in the remaining 65 stations (broadband, strong motion, GPS sensors) of the new Chilean network, which was planned by the University of Chile prior to the February 27, 2010 Maule earthquake, and is rapidly moving into the implementation phase. Cooperative action between the University of Chile, IRIS and the USGS National Earthquake Information Center (NEIC) will support procedures for establishing data collection, processing, archiving and open data access. NEIC will share its experience in earthquake monitoring, assessment and reporting with the University of Chile and the Chilean Ministry of the Interior’s Office of National Emergency (ONEMI) with the goal of improving the timeliness and effectiveness of earthquake alerts, public notices and general intra- and inter-governmental actions. Additional objectives in the collaboration are professional development in operational and analytical skills and fostering multi-disciplinary research collaboration between academic institutions. IRIS and USGS will use our experience in Chile to inform and document a model for strengthening national networks through international cooperation in training and development. We discuss aspects of this model, how it is being applied in Chile and the prospects for implementation in other countries.
Session:The Seismo-Acoustic Wavefield
Presenter   Kromer, Richard
Schedule   Fri AM / Poster
Room   Ballroom B
Acoustic/Infrasound Sensor Test Capability for the AFTAC Pinedale Seismic Research Facility
KROMER, R. P., RPKromer Professional/Technical Services, Albuquerque, NM, rpkromer@comcast.net
RPKromer PTS is developing specialized test equipment to characterize and calibrate acoustic/infrasound sensors for AFTAC seismo-acoustic application. The test equipment will eventually be deployed at AFTACs Pinedale Seismic Research Facility (PSRF) as part of an upgrade to the site’s capabilities for the production testing of geophysical instrumentation; components, subsystems and systems. Sandia National Laboratories is developing data base and analysis tools for sensor testing. Two testbeds are under parallel development. The first testbed uses an acoustic header-based signal source to simultaneously test the dynamic performance of up to four acoustic/infrasound sensors. State of health information such as sensor temperature, local barometric pressure and piston phase are also recorded.A second testbed uses an isolation chamber to measure up to four acoustic/infrasound sensor static self-noise. Dynamic acoustic signal generation capabilities will also be provided. State of health information such as chamber temperature, chamber internal barometric pressure and piston phase are also recorded. There are plans to control the chamber internal pressure to measure sensor performance at different altitudes.A Geotech Instruments SMART24 data logger calibrator controls a piston-based acoustic signal generator capable of generating sinusoidal, multi-tonal, step and white noise signals over a range of 0.1 to 50 Hz. Calibrated reference sensors will provide traceability to NIST when necessary. The data from the four sensors under test and reference sensors are acquired by the SMART24 digitizer channels.This poster will cover the development of the testbeds, some of the characteristics of the test equipment and the challenges of providing traceability.
Session:Earth Structure Observations and Theory
Presenter   Gassiyev, Aslan
Schedule   Thu 10:30 AM / Oral
Room   Ballroom E
Effective Physical Characteristics of Inhomogeneous and Anisotropic Uppermost Mantle in Pair Correlation Approximation
CHESNOKOV, E. M., University of Houston, Houston, TX, emchesno@mail.uh.edu; GASSIYEV, A., University of Houston, Houston, TX, aslan_116@yahoo.com
Difficulties in exploration and production of hydrocarbons drove more and more attention of scientists to understand and model the physical properties of the Earth crust. Most of those models have been proven to be valid by measurements and direct observations. Deeper parts of Earth, however, have been studied relatively less and no measurements other than surface seismic and laboratory experiments can confirm our observations. In this work, we describe the effective physical characteristics of uppermost mantle (up to 410 km discontinuity). The major phase (~60%) of the uppermost mantle is olivine (Mg, Fe)2 SiO4. It has been observed from surface seismic data that physical (elastic) properties of the uppermost mantle possess anisotropic character. Most popular explanation of anisotropy lies in the statistically ordered structure that is formed as a result of rotation of olivine grains during the flow in the uppermost mantle and also in plastic deformation of olivine by way of intra-granular slippage (Bugayevskiy and Chesnokov, 1986). Areas that create the strong preferred orientation are mostly areas of mantle upwellings (oceanic rifts). The anisotropy due to preferential alignment of crystals during mantle convection has been first pointed by Hess (1964). Polycrystalline media of multi-minerallic composition cannot be described analytically being a many body problem. The approximation technique applied in this work is the pair correlation approximation (PCA). The expressions of effective elastic tensors through their fluctuations are described using mass operator. To derive expressions for mass operators we used Dyson’s approach.Most of the models that have been proposed so far are static. Therefore, the provided correlation approximation accounts for the distribution of olivine minerals as a function of coordinate (space statistics), angles of orientation of crystallographic axes (Euler angles), aspect ratios, pressure, temperature and time.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Munson, Clifford
Schedule   Fri 2:00 PM / Oral
Room   Ballroom D
Evaluation of CAV as a Screening Criterion for Probabilistic Seismic Hazard Analysis
MUNSON, C. G., U.S. Nuclear Regulatory Commission, Washington, DC , cgm1@nrc.gov; AKE, J., U.S. Nuclear Regulatory Commission, Washington, DC, jon.ake@nrc.gov
Recently the strong-motion parameter Cumulative Absolute Velocity (CAV) has been used as a minimum-damage threshold for Probabilistic Seismic Hazard Analyses (PSHA), performed for siting critical facilities such as nuclear power plants. For these PSHA, a CAV value above 0.16g-sec has replaced the simple lower-bound magnitude cutoff of mb > 5 as the criterion to distinguish between damaging earthquake motions and non-damaging earthquake motions for well-engineered structures. Predictive equations for CAV, based on magnitude, peak ground acceleration, and local site conditions have been developed to remove small earthquakes with low damage potential from the PSHA. To evaluate the use of CAV as a screening tool for PSHA, we have examined many of the strong-motion recordings from the Next Generation Attenuation (NGA) data set. For these recordings we compare CAV to other strong motion parameters such as Spectral Intensity (SI) and Arias Intensity (Ia). Traditionally, CAV has been used as one of the shutdown criteria for nuclear power plants. As such, we also compare CAV to the response spectral acceleration and velocity checks also used for shutdown of nuclear power plants. Our preliminary results indicate that strong motions below the CAV<0.16g-sec threshold can have fairly significant spectral intensities; however, the durations of these ground motions are very small. Further evaluation to determine if there are significant ground motions below the CAV threshold is ongoing.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Cotton, Fabrice
Schedule   Wed 9:45 AM / Oral
Room   Room 204/205
Toward new single-station sigma models
RODRIGUEZ-MAREK, A., Virginia Tech, Blacksburg, VA, adrianrm@vt.edu; COTTON, F., Université Joseph Fourier, CNRS, France, fabrice.cotton@obs.ujf-grenoble.fr; ABRAHAMSON, N., Pacific Gas and Electric Company, University of Berkeley, Berkeley, CA, ; AKKAR, S., Middle East Technical University, Turkey, ; AL-ATIK, L., University of California at Berkeley, Berkeley, CA, ; ANDERSON, J., University of Reno, Reno, NV, ; BONILLA, L. F., Laboratoire des Ponts et Chaussées, France, ; BOMMER, J., Imperial College, United Kingdom, ; BUNGUM, H., NORSAR, Norway; DOUGLAS, J., BRGM, France; DROUET, S., Université Joseph Fourier, France; EDWARDS, B., ETHZ, Switzerland; FAEH, D., ETHZ, Switzerland; MONTALVA, G.,University of Concepción, Chili; DAWOOD, H., Virginia Tech, USA; RENAULT, P., Swiss-Nuclear, Switzerland; SCHERBAUM, F., Postdam University, Germany and STRASSER, F., Council for Geoscience, South Africa
Single-station sigma values for more than 600 stations have been computed using the same method for all records and datasets from different tectonic regions (California, Taiwan, Japan, Turkey, Mexico, Switzerland and France). This work has been driven by the need to develop better estimates of standard deviation for non-ergodic probabilistic seismic hazard assessment in Switzerland (PEGASOS Refinement Project), and for new ground motion models being developed for eastern North America (NGA-east) and western North America (NGA-west2). The results show that the average single-station standard deviations are lower than the ergodic values of standard deviation. Moreover, the single-station within-event standard deviations appear to have little variability across different tectonic regions. However, there is significant variability between stations and, in some instances, values of single-station standard deviation are higher than their ergodic counterpart. This variability seems to be (on the first order) controlled by path effects, and it can be modelled by probability distribution functions. Our results also show that the Vs30 dependency is weak, while a reduction of the within-event standard deviation is apparent with increasing distance (and magnitude). We finally amalgamate all within-event residuals from the different tectonic regions in order to propose and test several within-event single-station sigma models (constant, distance-dependent, distance and magnitude-dependent).
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Castellaro, Silvia
Schedule   Thu 11:00 AM / Oral
Room   Room 204/205
Seismic soil classification from a different perspective
CASTELLARO, S., Dipartimento di Fisica, Università di Bologna, Bologna, Italy, ; MULARGIA, F., Dipartimento di Fisica, Università di Bologna, Bologna, Italy,
The simplified seismic soil classification in many countries still basically relies on the Vs30 parameter as a proxy to the amplification factor. The pros and cons of this approach have already been extensively debated in the literature.We present an attempt to classify the subsoils in a seismic perspective which is based on expedite geophysical field procedures (passive/active single station and multichannel surveys, all based on the surface waves analysis) aimed at determining the resonance frequencies and the very shallow Vs profile.We will show how the same effort used to measure Vs30 can be used to overcome many limits of a Vs30-based classification and to get more representative classifications.In particular, this approach 1) implies accepting the concept that the site class is not a "universal" concept but is strictly linked to the type of structure which is planned to be built on that site, 2) implies a shift from the "depth-domain” concept (30 m or 20 m or 10 m suggested by different authors) to the "frequency-domain" concept and 3) does not take into account a somehow "averaged" stiffness but the abrupt stiffness changes, which play a big role in seismic amplification.Last, the role of velocity inversions (i.e. negative Vs gradients) will also be considered from the "frequency-domain" point of view.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Aiken, Chastity
Schedule   Wed AM / Poster
Room   Ballroom B
Dynamic Triggering of Microearthquakes at Three Geothermal Regions in California
AIKEN, C., Georgia Institute of Technology, Atlanta, GA, chastity.aiken@gatech.edu; PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng@gatech.edu; WU, C., Georgia Institute of Technology, Atlanta, GA, chunquanwu@gatech.edu
Recent studies have shown that microearthquakes can be dynamically triggered by the passing of surface waves from regional and teleseismic events. However, the underlying physical mechanisms and the necessary conditions that favor dynamic triggering are still in debate. Here we conduct a systematic search of dynamically triggered microearthquakes around the Long Valley Caldera (LVC), Coso Geothermal Field (CGF), and the Geysers in California. In each region, we select distant mainshocks in 1999-2010 with M>=7.5 over 1000 km away, or M>=5.5 between 100-2500 km. Next, we apply 2-8, 2-16, or 10-30 Hz band-pass-filtered data to the three-component seismograms recorded at each region, and identify triggered events as high-frequency seismic energy during large-amplitude surface waves of and teleseismic events. We calculate the beta statistic values based on events listed in the local earthquake catalogs and hand-picked events from the envelope functions, and verify that the triggering is statistically significant. Based on this simple procedure, we have identified many events that have triggered activity in each of the regions, including the recent 08/03/2009 and 04/04/2010 Baja California earthquakes at regional distances, and the 02/27/2010 Chile earthquake at teleseismic distances. Our next steps are to examine the dynamic triggering thresholds in each region, and to understand the triggering potential in terms of frequency, amplitude, incident angle, and type of surface waves.
Session:Geotechnical Lessons Learned from Recent Earthquakes: Haiti, Chile, Baja CA, New Zealand
Presenter   Hough, Susan
Schedule   Fri 9:15 AM / Oral
Room   Room 204/205
Localized Damage Associated with Topographic Amplification During the 12 January 2010 Haiti Earthquake
HOUGH, S. E., U.S. Geological Survey, Pasadena, CA, hough@usgs.gov; YONG, A., U.S. Geological Survey, Pasadena, CA, yong@usgs.gov; ALTIDOR, J. R., Bureau des Mines et de l'Energie, Port-au-Prince, Haiti, jnroalitdor@yahoo.fr; ANGLADE, D., Bureau des Mines et de l'Energie, Port-au-Prince, Haiti, ; GIVEN, D., U.S. Geological Survey, Pasadena, CA, doug@usgs.gov; MILDOR, S. L., Bureau des Mines et de l'Energie, Port-au-Prince, Haiti,
The staggering extent of damage and loss-of-life in the 12 January 2010 M7.0 Haiti earthquake was primarily caused by poor construction quality and high population density, in particular in the capital city of Port-au-Prince. Port-au-Prince is located in the southwestern corner of the Cul de Sac Valley, a large former deep marine basin extending into the Dominican Republic. Much of the city is underlain by a Mio-Pliocene fan complex characterized by small-scale topographic relief. Analysis of aftershocks recorded by portable strong motion instruments reveals, as expected, amplification of weak ground motions within the valley. The strongest inferred amplifications, however, are at two sites along a steep foothill ridge. The steepness of the topography as well as direct estimates from surface-wave techniques (Cox et al., in review, 2010) indicate that the ridge is characterized by higher shallow impedance than the surrounding region. The observed amplifications, which reach factors of 4-5 for frequencies ranging from a few to 10 Hz, thus cannot be explained by traditional near-surface sediment-induced amplification. The amplitude, predominant frequencies, and variability of response along the foothill ridge are consistent with predicted topographic amplification within a wedge. Deployment of a dense array of instrumentation would be useful to fully characterize topographic effects, but would be difficult due to highly challenging field conditions. However, the damage distribution provides an independent, complex but spatially rich data set. We consider the distribution of damage as determined from optical imagery, and show that a swath of unusually high damage corresponds with the extent of the ridge where high amplifications are observed. The damage distribution suggests a general correlation between severe damage and small-scale topographic relief. We explore approaches to characterize the topographic features that correlate with damage.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Bockholt, Blaine
Schedule   Thu AM / Poster
Room   Ballroom B
The Search for Non-Volcanic Tremor on the Reelfoot Fault, Northern Tennessee
BOCKHOLT, B., CERI, University of Memphis, Memphis, TN, boc06001@byui.edu; THOMPSON, L., CERI, University of Memphis, Memphis, TN, lthmpsn5@memphis.edu; DESHON, H., CERI, University of Memphis, Memphis, TN, hdeshon@memphis.edu; HORTON, S., CERI, University of Memphis, Memphis, TN, shorton@memphis.edu; LANGSTON, C., CERI, University of Memphis, Memphis, TN, clangstn@memphis.edu
An unusual micro tremor swarm was detected during an active source experiment in November 2006 near Mooring, Tennessee, within the New Madrid Seismic Zone. A phased array of 19 broadband seismometers has been deployed in the same area since November 2009 in an attempt to observe further micro tremor swarm activity that may have the characteristics of non-volcanic tremor (NVT) previously observed in the deeper levels of the San Andreas fault zone. The array has a backward “L” shape, 600m to a side, which takes advantage of farm field geometry in the area. We are primarily searching for signals with high phase velocity and western azimuths to corroborate the swarm events observed in 2006. The frequency band for presumed NVT is between 8 and 15 Hz and the array was designed to detect high phase velocity arrivals (3-25 km/s) from sources directly below that might originate on the Reelfoot thrust fault. We detect several sources of local ambient noise, such as well pumping and nearby trains, in addition to many microearthquakes. Although isolated small events of M-1 to M0, similar to those seen in 2006, show up as high phase velocity arrivals implying a source region directly below the array on the Reelfoot fault, we have not yet seen the same intense swarm-like activity that might be interpreted as tremor source. Array data are continuing to be collected and we will report on results for 2010.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Hough, Susan
Schedule   Wed 9:00 AM / Oral
Room   Ballroom C
The 1811-1812 New Madrid Earthquake Sequence
HOUGH, S. E., U.S. Geological Survey, Pasadena, CA, hough@usgs.gov; PAGE, M. T., U.S. Geological Survey, Pasadena, CA, mpage@usgs.gov
Documented macroseismic effects of the 1811-1812 New Madrid earthquake sequence provide the most direct constraint on the magnitudes of the principal events and the severity of shaking they generated. Some accounts that appeared to defy credulity are now understood to be consistent with the rupture scenario pieced together from a marriage of modern science and painstaking consideration of archival accounts. In fact, while one might suspect that early eyewitnesses would have been prone to exaggeration, extant archival accounts are overwhelmingly sober and credible – in a few cases even prescient – when considered with a modern understanding of earthquake ground motions. Quantitative interpretation of macroseismic effects is complicated by two fundamental limitations: 1) the limited number and fragmentary nature of the early accounts, and 2) the lack of instrumentally recorded large central/eastern US (CEUS) events to provide calibration. Near-field intensities are also difficult to determine because the most dramatic accounts can be attributed to secondary shaking effects that are now known to be unreliable indicators of shaking severity. Assigning intensity values from independent assessments by multiple researchers provides a reasonable characterization of macroseismic intensities at regional distances. Using the grid-search method developed by Bakun and Wentworth (1997) with available intensity-attenuation relations for the CEUS, we estimate magnitude values of 6.6-7.2 for the four principal events. The true uncertainties associated with these estimates are high and difficult to characterize. However, the preferred values from this analysis are, in combination with the recurrence rate inferred from paleoliquefaction studies, roughly consistent with the moment release rate predicted from post-glacial rebound, and not inconsistent with the low strain rate revealed by modern GPS data.
Session:Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Presenter   Assumpcao, Marcelo
Schedule   Thu 2:45 PM / Oral
Room   Ballroom C
Seismicity and Neotectonics in the Coastal Ranges of SE Brazil (Serra do Mar): a Case of Activity Migration ?
ASSUMPCAO, M., IAG, University of Sao Paulo, Sao Paulo, SP, Brazil, marcelo@iag.usp.br; RICCOMINI, C., Geosciences Institute, University of Sao Paulo, Sao Paulo, SP, Brazil, riccomin@usp.br
Intraplate seismicity in SE Brazil is presently distributed in two main areas: 1) offshore, roughly along the continental slope, where earthquakes with magnitude 5 occur every 15-20 years, and 2) away from the coast, in a broad zone covering the southern part of the Archean São Francisco craton and adjacent Neoproterozoic Brasília fold belt affected by Late Cretaceous intraplate magmatism (such as the 80-60 Ma Alto Paranaíba Igneous Province), and have a return period of ~100 years for magnitude 5. In the offshore zone, reverse faulting predominates and flexural stresses due to sediment load in the continental shelf are an important contributing factor. In the inland zone, the regional stresses are roughly characterized by E-W compression and N-S extension, probably with a thinned lithosphere concentrating stresses in the upper crust. Between the two seismic zones, the Serra do Mar coastal ranges, with steep topography and up to 2000 m altitude, is presently aseismic but had intense faulting during the Quaternary and even Holocene times. Stresses varied from compressional to extensional during this recent period, as mapped by tens of faults with clear striae. Some of these neotectonic faults are younger than 10,000 years B.P. The large number of neotectonic faults mapped in the Serra do Mar coastal ranges seem inconsistent with the present aseismic nature of this region. We propose that long term migration of seismicity is the cause of the present aseismic nature of the Serra do Mar coastal range.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Fujita, Kazuya
Schedule   Thu PM / Poster
Room   Ballroom B
A Re-examination of the Northern Illinois Earthquake of 1909
HUYSKEN, K. T., Dept. of Geosciences, Indiana University Northwest, Gary, IN, khuysken@iun.edu; FUJITA, K., Dept. of Geological Sciences, Michigan State University, East Lansing, MI,
The epicenter of the 1909 M 5.1 northern Illinois earthquake (the so-called “Aurora earthquake”) has been assigned to various localities located from the Wisconsin border to northern Will County; the later based on high intensity estimates for the western Chicago suburbs. We have re-examined over 400 newspaper reports from seven states and reassigned intensities giving preference to local reports; many wire service reports prove to be exaggerated, unreliable, or later retracted. The felt area is larger than previously reported, extending from the Ohio River to northern Wisconsin and from Lansing, Michigan, to near Des Moines, Iowa. The geometric center of the felt area, falls near LaSalle, Illinois, between the Fox and Illinois Rivers; the highest intensity, VII, is assigned to Morris, Illinois. Damage in many places (especially in Bloomington, Aurora, western Chicago, Kenosha, and Platteville) was not as severe as initially reported or not supported by local newspapers. Conversely, some local reports of extensive damage (e.g., Morris, Illinois) were not reported by syndicated news media. Local intensities are also affected by site effects. The scatter in intensities precludes use of intensity vrs distance relations except to place the event in north-central Illinois. The distribution of felt area and intensities are, however, similar to the mb 4.2 northern Illinois earthquake of June 28, 2004, which also has an instrumental epicenter near LaSalle, suggesting that the 1909 event occurred further south and west than previously proposed and farther from the Chicago metropolitan area.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Love, Jeffrey
Schedule   Wed AM / Poster
Room   Ballroom B
On the reported ionospheric precursor of the 1999 Hector Mine, California earthquake
THOMAS, J. N., Digipen Institute of Technology, Redmond, WA, jnt@uw.edu; LOVE, J. J., USGS Geomagnetism Program, Denver, CO, ; KOMJATHY, A., NASA - Jet Propulsion Laboratory, Pasadena, CA, ; VERKHOGLYADOVA, O. P., NASA - Jet Propulsion Laboratory, Pasadena, CA,
Reliable earthquake prediction is a worthwhile goal that, if ever attained, would reduce the loss of life and property. Unfortunately, it is not at all clear that earthquake prediction is either possible or practical, and the entire subject remains controversial. Still, some claims of success have been published, and among these are reports of perturbations in the ionosphere prior to large earthquakes. One example is the report of Pulinets et al. (Adv. Space Res., 39, 970-977, 2007) of ionospheric anomalies prior to the 16 Oct. 1999 Hector Mine, California earthquake. Using Global Positioning System (GPS) data recorded near the epicenter of the earthquake, they identify anomalous precursory changes in the ionospheric total electron count (TEC). In a check of their results, and to investigate whether solar-terrestrial or atmospheric drivers might have caused the reported ionospheric anomalies, we examine (1) multiple year-long TEC time series, derived from GPS stations both near and far from the earthquake epicenter, and (2) auxiliary data sets (e.g., geomagnetic, solar radio flux, sunspot count). We find that TEC anomalies are observed long before and after the Hector Mine earthquake. Moreover, the TEC anomaly prior to the earthquake starting on about 10 Oct. is coincident with changes in the Dst and Kp geomagnetic indices, solar radio flux, and sunspot count. Therefore, the TEC anomaly reported by Pulinets et al. was likely driven by solar terrestrial interactions and is unrelated to the Hector Mine earthquake.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Petersen, Mark
Schedule   Thu 2:15 PM / Oral
Room   Ballroom E
Key Science Issues in the Central and Eastern United States for the Next Version of the USGS National Seismic Hazard Maps
PETERSON, M. D., USGS, Golden, CO, mpetersen@usgs.gov; MUELLER, C. S., USGS, Golden, CO, cmueller@usgs.gov
The USGS National Seismic Hazard Maps are updated about every six years by incorporating newly vetted science on earthquakes and ground motions. The 2008 hazard maps for the central and eastern United States region (CEUS) were updated by using revised New Madrid and Charleston source models, an updated seismicity catalog and an estimate of magnitude uncertainties, a distribution of maximum magnitudes, and several new ground-motion prediction equations. The new models resulted in significant ground-motion changes at 5 Hz and 1 Hz spectral acceleration with 5% damping compared to the 2002 version of the hazard maps. The 2008 maps have now been incorporated into the 2009 NEHRP Recommended Provisions, the 2010 ASCE-7 Standard, and the 2012 International Building Code. The USGS is now planning the next update of the seismic hazard maps, which will be provided to the code committees in December 2013. Science issues that will be considered for introduction into the CEUS maps include: 1) updated recurrence models for New Madrid sources, including new geodetic models and magnitude estimates; 2) new earthquake sources and techniques considered in the 2010 model developed by the nuclear industry; 3) new NGA-East ground-motion models (currently under development); and 4) updated earthquake catalogs. We will hold a regional workshop in late 2011 or early 2012 to discuss these and other issues that will affect the seismic hazard evaluation in the CEUS.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   So, Emily
Schedule   Fri AM / Poster
Room   Ballroom B
Estimating Shaking-induced Casualties and Building Damage for Global Earthquakes
SO, E. K. M., U.S. Geological Survey, Golden, CO, eso@usgs.gov; SPENCE, R. J. S., Cambridge Architectural Research Ltd., Cambridge, United Kingdom, robin.spence@carltd.com; JAISWAL, K. S., U.S. Geological Survey (contracted through- Synergetics Inc.), Golden, CO, kjaiswal@usgs.gov
Recent earthquakes such as the Port-au-Prince, Haiti earthquake of 12 January 2010 have highlighted the importance of rapid estimation of casualties for humanitarian response. This paper describes the ongoing efforts to estimate global earthquake casualties in the U.S. Geological Survey’s (USGS) Prompt Assessment of Global Earthquakes for Response (PAGER) system. At present, the operational PAGER system uses empirical loss models that are derived purely from past fatality data in a given country or region. PAGER’s semi-empirical and analytical approaches do exist; however, they will require refinements to their building stock inventory and vulnerability functions. In addition, the semi-empirical approach relies on empirical data on building collapses and expert-opinion for deriving vulnerability functions where data are lacking.The loss-estimation method described in this paper allows refinement to the existing semi-empirical approach in which we estimate damage rates for different classes of buildings present in the local building stock, and then relate fatality rates to the damage rates of each building class. This approach makes it possible to account for the effects of the very different types of buildings (by climate, urban or rural location, culture, income level, etc.), and their mix. The analyses use empirical damage and casualty data assembled in the Cambridge Earthquake Impacts Database (CEQID) to explore the relationships of building and fatality distributions to the main explanatory variables of building type, damage level, and earthquake intensity. The resulting fatality rates were tested against the overall casualty data from several historical earthquakes, and a reasonable fit was found. Although there is still much to do to create a fully operational procedure, this approach is under development within PAGER as our continual efforts to improve the accuracy of rapid assessments of damage and human impact immediately following global earthquakes.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Huyck, Charles
Schedule   Fri 4:30 PM / Oral
Room   Ballroom D
GED4GEM: a global exposure database for the Global Earthquake Model initiative
GAMBA, P., University of Pavia, Pavia, Italy, paolo.gamba@unipv.it; JAISWAL, K., United States Geological Survey, Golden, CO, kjaiswal@usgs.gov; CROWLEY, H., Global Earthquake Model, Pavia, Italy, helen.crowley@globalquakemodel.org; HUYCK, C., ImageCat, Inc., Long Beach, CA, ckh@imagecatinc.com
The GED4GEM project aims at the realization of first publicly available Global Exposure Database (GED) that will facilitate global earthquake damage, loss and human casualty estimation within the Global Earthquake Model (GEM) framework (www.globalquakemodel.org/). Through the consortium of leading institutions and by engaging the domain-experts from multiple countries, GED4GEM not only attempts to harmonize the best exposure datasets that are available worldwide but also aims to incorporate the best practices in the creation of exposure datasets at places where such efforts are lacking. This investigation outlines the ongoing developments for creation of GED, and discusses the challenges associated with such processes. To begin such developments, GED first uses the default inventory available through the USGS PAGER system. The PAGER effort represents a significant progress in statistical characterization of structural type by country, the leveraging of existing global datasets, and a proven methods of extrapolating structural parameters from UN housing and demographic data. Significant efforts are necessary beyond PAGER, to estimate the missing attributes of the exposure data, and to develop mapping schemes to accommodate recent or newly found data-sources that provide detailed inventory of building stock and other socio-economic indicators. Accordingly, meaningful and semi-automatic algorithms for the fusion of the information available from different sources in order to obtain geographically multi-scale statistically consistent information will be developed by the GED4GEM consortium. GED uses a database structure that is compliant to the Open Geospatial Consortium recommendations and is consistent with the OpenGEM architecture. Spatial databases with variable resolutions and structures will be linked appropriately, and standards-based tools will also be developed to support access, querying capabilities, and visualization functions.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Tibuleac, Ileana
Schedule   Wed PM / Poster
Room   Ballroom B
Higher resolution seismic velocity model in the Reno Basin
TIBULEAC, I. M., University of Nevada, Reno, NV, imtseismic@yahoo.com; VON SEGGERN, D. H., University of Nevada, Reno, NV, vonseg@seismo.unr.edu; LOUIE, J., University of Nevada, Reno, NV, louie@seismo.unr.edu; SMITH, K., University of Nevada, Reno, NV, smith@seismo.unr.edu
An accurate shallow velocity model in the Reno Basin is crucial for understanding of earthquake ground motions and their variability in the Reno and Carson City region and for realistic quantification of seismic hazard. Geologic evidence in this region indicates the potential for large magnitude (M7-7.5) events occurring on local faults, such as the Mt. Rose and Genoa Faults. However, there is a gap in the high resolution shear velocity models in the Reno Basin from 200 m to 3 km.In this study, we derive a new velocity model with improved resolution in the upper three km from using seismic interferometry. We process continuous ambient seismic noise recorded by permanent as well as temporary (March-July 2008) broadband and short - period instrument deployments in the Reno Basin.We have developed algorithms for extracting ambient noise-derived Green’s Functions, which are used to derive velocity models in the Reno Basin, for inter-station distance from hundreds of meters to 60 km, and for different instrument-types. These algorithms include modifications to account for distance dependent filtering and data processing after conversion into records of the same instrument type, i.e. broadband with 0.1 Hz corner frequency. Hundreds of inter-station paths are analyzed, yielding high resolution in the upper three km, especially in the northern part of the Reno Basin. In this study, we are overcoming the limitations of seismic tomography, which in Reno depends on a non-uniform source area distribution. We use autocorrelations and crosscorrelations to recover the surface waves and body - wave reflections from ambient noise-derived Green’s Functions at each sensor, and between pairs of sensors. The estimated shallow seismic velocity model constraints are integrated with the existing Reno Basin velocity models.
Session:Guide to Sustainable Seismographic Networks
Presenter   Anderson, Kent
Schedule   Fri PM / Poster
Room   Ballroom B
The GSN Data Quality Initiative
ANDERSON, K. R., Incorporated Research Institutions for Seismology, Washington, DC, kent@iris.edu; DAVIS, P., University of California, San Diego, IGPP, La Jolla, CA, pdavis@ucsd.edu; GEE, L., USGS - Albuquerque Seismological Laboratory, Albuquerque, NM, lgee@usgs.gov
The Global Seismographic Network (GSN) is undertaking a renewed effort to assessand assure data quality that builds upon completion of the major installation phase of the GSN and recent funding to recapitalize most of the network’s equipment including data acquisition systems, ancillary equipment and secondary sensors. We highlight here work by the network operators, the USGS’ Albuquerque Seismological Lab and UCSD’s Project IDA, to ensure that both the quality of the waveforms collected is maximized, that the published metadata accurately reflect the instrument response of the data acquisitions systems, and that data users are informed of the status of the GSN data quality.Procedures to evaluate waveform quality blend tools made available through the IRIS DMC’s Quality Analysis Control Kit (http://www.iris.washington.edu/QUACK/), analysis results provided by the Lamont Waveform Quality Center (www.ldeo.columbia.edu/~ekstrom/Projects/WQC.html), and custom software developed by each of the operators to identify and track known hardware failure modes. Each operator’s equipment upgrade schedule is updated periodically to address sensors identified as failing or problematic and for which replacements are available. Particular attention is also paid to monitoring the GPS clock signal to guarantee that the data are timed properly.Devices based on GPS technology unavailable when the GSN began 25 years ago are being integrated into operations to verify sensor orientations. Portable, broadband seismometers whose stable response can be verified in the laboratory are now co-located with GSN sensors during field visits to verify the existing GSN sensors’ sensitivity. Additional effort is being made to analyze past calibration signals and to check the system response functions of the secondary broadband sensors at GSN sites. The new generation of data acquisition systems will enable relative calibrations to be performed more frequently than was possible in the past.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Moschetti, Morgan
Schedule   Wed PM / Poster
Room   Ballroom B
Testing the Wasatch Community Velocity Model with long period (T > 2 s) ground motion simulations
MOSCHETTI, M. P., US Geological Survey, Golden, CO, mmoschetti@usgs.gov; RAMIREZ-GUZMAN, L., US Geological Survey, Golden, CO, lramirezguzman@usgs.gov
The Wasatch Fault bounds the Salt Lake Basin (SLB), Utah to the east and is capable of producing M7 earthquakes. To characterize the seismic hazard along the Wasatch Front posed by large events on this fault, we require estimates of potential earthquake ground motions. Previous and on-going studies (Liu et al., 2010; Roten et al., 2010) examine earthquake ground motions caused by simulated M7 events on the Salt Lake Segment of the Wasatch Fault using the Wasatch Community Velocity Model (WCVM) (Magistrale et al., 2006). However, a comprehensive validation of the WCVM has not yet been performed. By perturbing the seismic velocities of the WCVM and comparing observed and synthetic seismograms, we identify simple model perturbations that improve the model. Our investigation focuses on the regional velocity model and on the empirical wave speed relations used to determine deep-basin seismic velocities because the basin wave speeds in the shallowest part of the model are well-constrained by seismological and geotechnical measurements. We simulate moderate-sized (M3-5) earthquakes and surface impulses using the Hercules finite element tool-chain (Tu et al., 2006) to retrieve synthetic earthquake seismograms and inter-station Green’s functions at the locations of the broadband and strong-motion seismometers in the Wasatch Front region. We then identify those perturbations that reduce waveform discrepancies, by comparing synthetic and observed seismograms, and document the differences in arrival times and peak ground velocities. Comparisons between the simulated inter-station Green’s functions and the vertical-vertical noise correlation functions employ surface wave dispersion measurements. Unresolved differences between the observed and synthetic seismograms that persist are likely due to un-modeled heterogeneities and improper basin geometries. Future modeling efforts in the Wasatch Front may apply these results for improved earthquake ground motion estimates.
Session:Guide to Sustainable Seismographic Networks
Presenter   Lockhart, Andrew
Schedule   Fri PM / Poster
Room   Ballroom B
Network Installations and Enhancements in Developing Countries: 25 Years of VDAP Experience.
LOCKHART, A. B., US Geological Survey, Vancouver, WA, ablock@usgs.gov
The USGS/USAID Volcano Disaster Assistance Program (VDAP) has a long history transferring volcano-monitoring networks to developing countries. Since 1986 VDAP staff have installed or augmented networks on more than 40 volcanoes in 13 developing countries and on approximately 14 volcanoes domestically. VDAP equipment and training efforts focus on long-term sustainability and institution-building in the service of volcano hazard mitigation.A broad survey of long-term results shows good but variable sustainability. Some factors controlling sustainability can be influenced, others not. The two most important uncontrollable factors are the culture of the specific monitoring institution and the overall development level of the country.Controllable factors include the simplicity of the network design and methods of installation and maintenance. Networks in tropical, condensing, marine environments require more protection from lightning, moisture and insects than most networks in temperate or subarctic zones. Also, lead-acid battery life is shorter in tropical environments than in cold.Training benefits are often ephemeral. They rarely propagate through some institutions or survive staffing changes. Repetition of fundamental training at some interval greatly increases the likelihood of its retention. Documentation which might mitigate this problem tends to be underutilized.Digital telemetry system installation is more straightforward than that of older analog equipment, but the Line-of-Sight and power requirements are more restrictive. Relative simplicity of digital equipment allows training to focus more on field engineering fundamentals that improve long-term sustainability.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Shome, Nilesh
Schedule   Thu 2:30 PM / Oral
Room   Ballroom E
Effect of B-Fault Recurrence Uncertainty on Hazard in the Los Angeles Area
SHOME, N., Risk Management Solutions, Inc, Newark, CA, nilesh@stanfordalumni.org; PERKINS, D., U S Geological Survey, Golden, CO,
Although a large number of different sources of uncertainties, e.g., characteristic magnitude of a fault, multiple fault, and deformation models, etc., has been considered in developing the national hazard maps, modeling the uncertainty in the recurrence rates has not been considered because of the focus on the estimation of mean hazard. Significant research has been carried out to quantify the uncertainty in the earthquake recurrence rates of the major faults (e.g., San Andreas fault) from the paleoseismic data. But limited research results are available to quantify the uncertainty in the slip rates of the type-B faults, and the slip rates exclusively define the recurrence rates of these faults. Since the type-B faults contribute significantly to the seismic hazard in Los Angeles, the effect of uncertainty in hazard in Los Angeles is estimated for these faults, using Monte Carlo simulation for several different assumptions on slip rate uncertainty to understand the importance of those on the hazard results.Although estimates for uncertainty of low recurrence rate faults have a considerable range of values, it is convenient to represent typical values by assuming that the two-sigma uncertainty in the slip rates of the type-B faults is about plus or minus 50 percent of the preferred rate, an additive uncertainty. An alternative view, based on likelihood principles, is times or divide a factor of 2, a multiplicative uncertainty. We present the range of the hazard results for selected sites, based on these alternative uncertainty models of the slip rates. In addition, for a hypothetical fault, we investigate the possible reduction of these ranges of uncertainty by combining geological and seismological rates using Bayes' theorem by associating one or more earthquakes to the fault. The issue of interdependency of slip rates among adjacent faults is also addressed.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Bausch, Doug
Schedule   Fri 3:30 PM / Oral
Room   Ballroom D
Development and Enhancement of Building Inventories for HAZUS
BAUSCH, D. B., FEMA Region VIII, Denver, CO, Douglas.Bausch@dhs.gov
FEMA has supported the development of building and infrastructure inventories for the purpose of HAZUS-based earthquake loss estimations in the U.S. This presentation will outline the history of and sources of the baseline inventories, as well as the methodology and applications of assigning earthquake building type mapping schemes and enhancement of inventories. We have undertaking significant improvement of the General Building Stock (GBS) inventories primarily through the application of tax assessor parcel data. A recent application of assessor data in Utah has led to a very significant refinement in potential losses and helped quantify the extensive losses that may occur as a result of the large stock of unreinforced masonry (URM) buildings constructed before the seismic threat was realized. Our loss estimation scenarios have frequently indicated just one building type drives the vast majority of fatalities and severe injuries. In both the Utah and New Madrid areas this has been the stock of URM buildings. The improved data indicate some 185,000 URMs in the Utah region and 450,000 URMs potentially impacted by the New Madrid seismic zone. Therefore, in cases of limited resources, inventory efforts should be focused on the most vulnerable building types. In Utah, we have recently launched several URM inventory efforts.In the U.S. we have also recently benefited from the development of the Homeland Security Infrastructure Protection (HSIP) Gold and Freedom national inventories of critical facilities and infrastructure. While these datasets do not ship with the free non-proprietary data available from FEMA, we have undertaken integrating HSIP data into the HAZUS model to support our mission. A significant annual investment in HSIP as resulted in year over year improvements in completeness and positional accuracy for a broad variety of datasets.
Session:Creative Wavefield Recording and Analysis
Presenter   Krasnova, Maria
Schedule   Fri 11:15 AM / Oral
Room   Ballroom E
Analysis of time variations in correction angles for horizontal components of downhole geophones
KRASNOVA, M. A., Institute of Physics of the Earth Russian Academy of Sciences, Moscow, Russia, mkrasnova@ifz.ru; CHESNOKOV, E. M., , Houston, TX, emchesno@mail.uh.edu
The determination of orientation of horizontal components of 3-C downhole geophones during passive monitoring of a hydraulic fracture using 186 perforation shots (perfshots)has been done. Besides, we found angles by which a coordinate system of frac event record should be rotated in order to consider all records in a unified coordinate system (correction angles). The analysis of correction angles was carried out for two observation wells during 8 stages of hydraulic pumping. The geophones were kept in the borehole during all these stages. As a result, we found a time dependence of the correction angles for all geophones in the both wells. The correction angles change for the both monitoring wells with a rate 0.03 – 0.1 deg/hour. This time dependence can be caused by a change in elastic anisotropy and existence of azimuthal anisotropy in layers penetrated by seismic waves. This is explained by the fact that in anisotropic medium the displacement in compressional wave does not coincide with the normal to wave front. In the VTI medium, the displacement and wave front normal are always in the vertical plane. However, in the case of azimuthal anisotropy, the vector-difference between these two directions has a horizontal component, and the vector-difference depends on the azimuth. The observed change in correction angle can be caused by two reasons: (1) a shift in perfshot position along the wellbore and (2) change in the elastic symmetry type, position of the symmetry axes, and anisotropy coefficient due to hydraulic fracturing.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Martin, Antony
Schedule   Wed PM / Poster
Room   Ballroom B
Preliminary results from ARRA-funded geotechnical site characterizations
MARTIN, A. J., GEOVision, Inc., Corona, CA, amartin@geovision.com; YONG, A., U.S. Geological Survey, Pasadena, CA, yong@usgs.gov; STOKOE, K. H., University of Texas, Austin, Austin, TX, k.stokoe@mail.utexas.edu; DIEHL, J. G., GEOVision, Inc., Corona, CA, jdiehl@geovision.com; JACK, A. D., GEOVision, Inc., Corona, CA, ajack_gss@msn.com; LEITH, W., U.S. Geological Survey, Reston, VA, wleith@usgs.gov
As part of the 2009 American Recovery and Reinvestment Act (ARRA) effort, the USGS contracted a consortium from academia and commerce to perform geotechnical site characterization at 189 seismographic station sites. We report preliminary results, involving surface-wave techniques, which include the horizontal-to-vertical spectral ratio (HVSR) technique and one or more of the following: spectral analysis of surface wave (SASW), active and passive multi-channel analysis of surface wave (MASW) and array microtremor methods. From this multi-method approach, we determine Vs (shear-wave velocity) profiles and the average shear-wave velocity of the upper 30 meters (Vs30) for each site. Field investigations have been conducted at a wide variety of sites, including rural and urban soil sites, as well as weathered and competent rock sites. Field procedures have been adapted to a wide variety of site conditions, e.g., P-wave seismic refraction is added at all rock sites to capture potential variations in lateral velocity due to differential weathering. Generally, the most difficult sites to characterize have been rock sites with the seismic station located at the edge of a bedrock outcrop, where thin sediment layers overlie high velocity, dipping bedrock beneath the survey location. At many of these sites the S-wave seismic refraction technique has been added to help characterize Vs structure. In general, Vs have been comparable to values expected from mapped geology; however, results at some sites do not reflect expected velocity structures and are attributed to lithologic complexities in the subsurface. Calculated Vs30 typically covers the full range of site classes from D/E (soft/stiff soil) to A (hard rock), although the vast majority of sites are in the Site Class D to B range. Our pilot project ends in September 2011 and an USGS Open File Report describing the surface geology, Vs profile and the calculated Vs30 for each site is expected to follow shortly after.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Hafner, Katrin
Schedule   Fri AM / Poster
Room   Ballroom B
Transportable Array in the Central and Eastern US: A Unique Opportunity for New Seismic Observations Relevant to Nuclear Power Plants
HAFNER, K., Incorporated Research Institutions of Seismology, Washington, DC, hafner@iris.edu; BUSBY, R. W., Incorporated Research Institutions of Seismology, Washington, DC, busby@iris.edu; WOODWARD, R. L., Incorporated Research Institutions of Seismology, Washington, DC, woodward@iris.edu
The USArray Transportable Array (TA) is a network of 400 seismograph stations that is systematically moving west-to-east across the contiguous United States. From 2011 to 2013 the TA will occupy ~800 station sites in the central and eastern US, and every existing or planned nuclear power plant in the eastern US will be within 70 km of at least four new seismic stations. Therefore, the TA station deployment in the eastern half of the US presents an unprecedented opportunity for improving source characterization, modeling the regional velocity and attenuation structure, and mapping seismic zones down to low magnitude thresholds. The TA is part of the National Science Foundation’s multi-disciplinary EarthScope program. The TA has already occupied over 1,000 stations in the western US and is continuing its multi-year migration towards the Atlantic coast before heading for Alaska. The stations use a grid-like deployment with 70 km separation between stations. At any given time there are approximately 400 stations operational, occupying a nominal 800 km by 2000 km “footprint.” The TA is presently installing stations in a north-south swath extending from Wisconsin to Louisiana and Alabama in the south. Each station is operated for two years, though organizations can “adopt” stations after installation so that the stations become permanent. An organization adopts a station by reimbursing the cost of the hardware, and working out a land-use agreement with the station landowner.TA stations consist of three component broadband seismometers, with a few sites in the westernmost United States also including three component strong motion instruments. The instruments are installed about two meters below the surface, in thermally stable vaults. All stations transmit continuous data in near-real-time at 40 sps. The data are freely distributed through the IRIS Data Management Center. TA stations can also be upgraded to incorporate high frequency or strong motion instruments.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Borcherdt, Roger
Schedule   Wed 11:00 AM / Oral
Room   Room 204/205
On Comparison of NGA and NEHRP Site Factors for Routine Design
BORCHERDT, R. D., United States Geological Survey, Menlo Park, CA, borcherdt@usgs.gov
The Next Generation Attenuation (NGA) effort has proven to be a major milestone in the compilation and estimation of strong motion for use in earthquake resistant design. Use of these advances in code provisions suggests the need to evaluate and quantify the consistency between the National Earthquake Hazard Reduction Program (NEHRP) site factors, presently used in building codes and those implied by the NGA relationships. Recent and ongoing comparisons by a number of researchers suggest the largest variability and uncertainty in both estimates of site factors exist for site-class E soils. These variations and uncertainties are due in part to: limited strong-motion data regarding the response of soft soils, wide variations in the response of layered soft soil deposits, variations in NGA models, and limitations of the simplified code model used to characterize the strongly frequency-dependent resonant seismic response of soft soils. Accounting for these variations is needed to quantify the comparison of NGA and NEHRP site factors. Data limitations and model variations for soft soils and their implications for comparison of NGA and NEHRP site factors will be discussed. With far sightedness, current code provisions have been developed to allow the latest results to be incorporated into estimates of design ground motions through the option to use site-specific procedures.
Session:Creative Wavefield Recording and Analysis
Presenter   Rubinstein, Justin
Schedule   Fri PM / Poster
Room   Ballroom B
Analysis and Modeling of the Wavefield Generated by Explosions at the San Andreas Fault Observatory at Depth
RUBINSTEIN, J. L., USGS, Menlo Park, CA, jrubinstein@usgs.gov; POLLITZ, F., USGS, Menlo Park, CA, fpollitz@usgs.gov; ELLSWORTH, W. L., USGS, Menlo Park, CA, ellsworth@usgs.gov
Using multiple deployments of an 80-element seismic array stretching from the surface to 2.4 km depth we examine recordings of chemical explosions to better understand the generation of shear waves by explosive sources. The chemical shots are small, between 5 and 10 pounds, and are adjacent to the well (approximately 40 m from the well head). The most prominent feature of the recordings is a very simple, strong, impulsive P arrival on the vertical channels. Additional, coherent phases arrive later on the vertical channel with the P velocity. Coherent energy at either the P or S velocities is less clear on the horizontal channels than the vertical channel. In addition to visually searching for shear waves, we examined attenuation in the near surface using both a spectral ratio method and a pulse width method. These methods indicate that the near surface is a highly attenuating medium, with QP between 20 and 50 in the upper 450 meters.We also compare our observations with synthetic waveforms on a suitable 1D structure using the Direct Radial Integration method of Friederich and Dalkolmo (1995), which handles a layered transversely isotropic medium with anelasticity. For a zero-offset, shallow-burial source the synthetics yield a highly impulsive P arrival in addition to a small S arrival. Given this result, we are now exploring f-k filtering methods to mute the P energy in our data so that we can search for the predicted S arrival. With dominant frequency between 70 and 100 Hz (depending on distance from the source), this dataset is amenable to waveform modeling to estimate the source time function, which is expected to shed light on the source radiation generated by chemical explosions and the interaction of shallow explosive sources with the free surface.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Boyd, Oliver
Schedule   Thu AM / Poster
Room   Ballroom B
Modeling surface deformation in the New Madrid seismic zone: What is the geodetic data telling us?
BOYD, O. S., U.S. Geological Survey, Memphis, TN, olboyd@usgs.gov; ZENG, Y., U.S. Geological Survey, Golden, CO, zeng@usgs.gov; RAMIREZ-GUZMAN, L., U.S. Geological Survey, Golden, CO, lramirezguzman@usgs.gov
We model the surface deformation associated with steady-state creep on deeply buried dislocations beneath the Mississippi embayment and post-earthquake viscoelastic relaxation from the 1811-1812 New Madrid earthquakes and compare these results with geodetic observations. This comparison has not previously been done primarily because of expectations of low signal-to-noise ratio for the geodetic data in this stable intraplate region of the North American plate. Improvements in the precision of geodetic measurements indicate very low rates of surface deformation, which, for models of steady-state creep on infinitely long dislocations, appear to be inconsistent with the return periods of large earthquakes in the New Madrid seismic zone. Resolution of this issue will help to constrain and address questions significant for earthquake hazard assessments. Our model that best fits the geodetic data involves 1.5 mm/yr of reverse-sense creep on a finite dislocation beneath the downdip extension of the Reelfoot fault, which is consistent with expectations of the sense of slip on the fault and explains 43% of the variance in the geodetic observations. In an alternative model with half the variance reduction, we find 3.5 mm/yr of right-lateral creep beneath the Cottonwood Grove fault, also consistent with expectations of the sense of slip on this fault. If modeled together, 1.5 mm/yr beneath both faults best explains the data with 46% variance reduction. For models involving viscoelastic relaxation, our best fitting model has 1 m of slip on both the Reelfoot and Cottonwood Grove faults during the 1811-1812 earthquake sequence and can explain 18% of the variance in the geodetic observations. We continue this investigation by 1) assessing the uncertainty in the geodetic observations resulting from white, flicker and random walk noise models and 2) studying the effect of a finite lower crustal dislocation in the presence of regional and far field drivers.
Session:Earth Structure Observations and Theory
Presenter   Karaoglu, Haydar
Schedule   Thu 10:45 AM / Oral
Room   Ballroom E
Strain-Energy Compatible Partition of Hooke’s Law --- Application to the Modeling of Intrinsic Attenuation in Wave Propagation
KARAOGLU, H., Carnegie Mellon University, Pittsburgh, PA, hkaraogl@andrew.cmu.edu; TABORDA, R., Carnegie Mellon University, Pittsburgh, PA, rtaborda@andrew.cmu.edu; BIELAK, J., Carnegie Mellon University, Pittsburgh, PA, jbielak@andrew.cmu.edu
We have previously reported on a memory-efficient displacement-based rheological model for incorporating intrinsic attenuation in solids for wave propagation problems, which we denoted as the BKT model. This model consists of a set of two parallel Maxwell elements and a Kelvin-Voigt element in parallel. It exhibits an almost constant quality factor (Q), with a maximum error of five percent with respect to any prescribed target value (Qo). Thus far, however, we have used the same quality factor for the P- and S-wave components of the wavefield. In this study, we use a strain-energy compatible partition of Hooke’s law of elasticity that allows us to incorporate distinct quality factors, QP and QS, associated to each type of energy into the formulation of the BKT model. In partitioning Hooke’s law, we show that the strain energy stored within the domain can be expressed as the combination of dilatational- and shear-strain components. This ensures that the different resulting parts associated to each quality factor are non-negative---a critical characteristic for the stability of wave propagation simulation once we add internal friction into the model. The proposed approach also allows us to observe more clearly the interaction between the dilatational and shear components of the strain energy in the wavefield, and how the material dissipates energy due to anelasticity as compared to the corresponding elastic case. We implement the proposed approach using finite elements to discretize the governing equations, and test and analyze the results for different numerical examples.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Chuang, Ray
Schedule   Fri 2:45 PM / Oral
Room   Ballroom E
3D crustal stress inversion using a mixed linear-nonlinear Bayesian inversion
CHUANG, R. Y., Indiana University, Bloomington, IN, chuangyu@indiana.edu; JOHNSON, K. M., Indiana University, Bloomington, IN, kajjohns@indiana.edu; WU, Y. M., National Taiwan University, Taipei, Taiwan, drymwu@ntu.edu.tw
Inversions for fault slip rates using kinematic crustal deformation models are typically constrained by geodetic observations. However, knowledge of the state of crustal stress is necessary in addition to kinematics, for constraining regional deformation models. We are currently working towards incorporating stress formally in probabilistic, Bayesian inversions of geodetic data for fault slip rates. To that end, we first determine the state of stress from focal mechanism data by using a mixed linear-nonlinear Bayesian inversion. We divide the region into cells and calculate five components of deviatoric stress tensor for each cell. In order to estimate a regional stress field, Hardebeck and Michael (2006) presented a damped least square inversion with 2D spatial smoothing assuming spatial correlation of the stress tensor. An optimal smoothing parameter is determined from a trade-off curve. However, the geometry of the curve depends on the scaling of the plot, and the choice of the parameter is therefore subjective.In this study, we develop a crustal stress inversion with 3D spatial smoothing and magnitude weighting. We adopt a mixed linear-nonlinear inversion using Markov Chain Monte Carlo (MCMC) Metropolis algorithm following the methodology of Fukuda and Johnson (2010) to objectively estimate the posterior probability distributions of the spatially-varying stress components and spatial smoothing parameter. The inversion is designed to identify which focal mechanism nodal plane is the more likely activated fault plane. We also incorporate Bayesian model selection to identify the optimal number of cells. We estimate the state of stress before and after the 1999 Chi-Chi earthquake using focal mechanism data from 1991-2008. Preliminary results show significant stress orientation changes across the earthquake, indicating ambient stress may be of the same order as coseismic stress drop.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Biasi, Glenn
Schedule   Wed AM / Poster
Room   Ballroom B
Crustal Velocity Structure in Nevada and Eastern California from Body-wave Tomography
BIASI, G. P., University of Nevada Reno, Reno, NV, glenn@seismo.unr.edu; PRESTON, L., Sandia National Laboratory, Albuquerque, NM, lpresto@sandia.gov
New P- and S-wave tomographic images of the crust and shallow mantle in Nevada and eastern California have been developed using a combination of Nevada permanent network and Earthscope Transportable Array station coverage. Over 130,000 direct and refracted P and direct S phases are used from ~6900 sources and 275 stations. Inversions use 10x10x5 km blocks and a total depth of 70 km in a modified Vidale-Hole least-time algorithm with variable regularization. Ray coverage is good throughout the study area below about 10 km. Resolution better than 20x20 horizontally is achieved in most of the study area, with better resolution the west where the permanent Nevada networks contribute most. P-wave velocities at 5-10 km depths are dominantly in the range of 5.5 to 6.35 km/sec, consistent with previous studies. At this depth the Sierra Nevada is clear as a coherent high-velocity block. Velocities are below average for much of southern and southeastern Nevada. Low velocities are also associated with extension in the Amargosa Valley, Mina, and Carson Sink areas. At 15-20 km lineations in crustal velocity coincide in many cases with important mapped faults including Owens Valley, the Mina Deflection, and the central and northern Walker Lane. A localized, deep high-velocity body correlates with the Silver Peak extensional complex in western Nevada. Vs generally correlates with Vp, but Vp/Vs maps suggest long-wavelength features including above average Vp/Vs in western Nevada near 39 north and along the state line, and below average in central and eastern Nevada. Velocity variations exhibit only weak correlations with Quaternary volcanic centers, consistent with sub-crustal sourcing and weak crustal controls on their locations.Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy s National Nuclear Security Administration under contract DE-AC04-94AL85000.
Session:Creative Wavefield Recording and Analysis
Presenter   Ford, Sean
Schedule   Fri PM / Poster
Room   Ballroom B
Seismic Observation of the Aurora
FORD, S. R., Lawrence Livermore National Laboratory, Livermore, CA, sean@llnl.gov
The aurora is observed in seismic recordings as an increase in low-frequency power. This increase in power corresponds with magnetic field measurements related to the onset of aurorae. The effect on the seismic recordings increases with distance to the magnetic pole and variations in the auroral effect are mapped with a spatially dense seismic network. Possible mechanisms for the magnetic response of the seismometer are discussed. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   McGarr, Art
Schedule   Thu 1:45 PM / Oral
Room   Room 204/205
Why Stress Drops and Apparent Stresses do Not Depend on Seismic Moment
MCGARR, A., USGS, Menlo Park, CA, mcgarr@usgs.gov; FLETCHER, J. B., USGS, Menlo Park, CA, jfetcher@usgs.gov; BOETTCHER, M., University of New Hampshire, Durham, NH, margaret.boettcher@unh.edu
McGarr et al. (Bull. Seism. Soc. Am., 2010) showed that slip rates of earthquakes are controlled by fault-zone yield stress and are independent of factors specific to a given earthquake, such as the distribution of slip. We have applied this result, in conjunction with laboratory friction data, to estimate maximum slip rates and stress parameters, including static stress drop and apparent stress, to earthquakes with magnitudes ranging from 2 to 7.9. For each earthquake, the stress parameters and the maximum slip rate are functions of the seismic moment and the maximum fault slip, usually determined from published slip models. The stress drops fall in the range 2.6 to 46 MPa and show no systematic dependence on seismic moment. Instead, it appears that the stress drops are influenced by variations in fault strength, which depends on depth, tectonic setting, pore pressure, material properties and whether the rupture process is frictional sliding or fresh rock fracture. Traditionally, the scaling of apparent stress has been difficult to assess because of bias introduced by factors such as band-limited recording. In our analysis, we have avoided these problems because our estimates of apparent stress are based only on the seismic moment and maximum slip, which are determined from low-frequency information. For the earthquakes in our study, the apparent stresses range from 0.7 to 12 MPa and also appear to be independent of seismic moment. Rather, apparent stress is a function of maximum slip rate, which depends on yield stress, and rupture speed. In general, we found no evidence suggesting that rupture physics for earthquakes of magnitude 2 differ from those for events with magnitudes as high as 7.9, at least in continental crustal settings. In particular, we conclude that stress drops and apparent stresses are independent of seismic moment because they are controlled by fault strength, which is independent of scale.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Ghosh, Abhijit
Schedule   Thu 11:45 AM / Oral
Room   Ballroom D
Tremor Depth Using Array of Arrays in Cascadia
GHOSH, A., University of Washington, Seattle, WA, aghosh.earth@gmail.com; VIDALE, J. E., University of Washington, Seattle, WA, seismoguy@mac.com; CREAGER, K. C., University of Washington, Seattle, WA, kcc@ess.washington.edu
We installed 8 small aperture seismic arrays in northern Washington to capture the intimate details of tremor activity in Cascadia. The Array of Arrays (AofA) focuses on the tremor-active megathrust in this region, including the area we previously imaged with a solo array in 2008 [Ghosh et al., GRL, 2009, 2010; Ghosh et al., G-cubed, 2010]. Since it became operational in June 2009, the AofA recorded several tremor episodes, including the recent Episodic Tremor and Slip (ETS) event in August 2010.We have developed a Multi-Beam Backprojection (MBBP) technique to image tremor in high resolution using data from multiple seismic arrays. We apply a beamforming technique at each array to stack the seismic energy at every 0.2 Hz from 2 to 20 Hz using 1-minute sliding time window. During tremor episodes, the arrays show stable slowness, and azimuth over the tremor frequency band (generally 3-8 Hz). We get the best slownesses from all the available arrays, and backproject to find the tremor source location. While P-wave energy stacks coherently up to 10 Hz and higher, S-wave extends only up to 6 Hz or so.The MBBP method is applied to the AofA data to detect and locate tremor. Initial results indicate that the MBBP technique is able to constrain tremor depth reasonably well. The majority of the tremor under the arrays is located near the plate interface, and aligns parallel to the dip of the interface. We are currently analyzing the entire ~15 months of data, which include the latest ETS event. The MBBP method reveals significantly longer duration of tremor activity, including the episodes that remain completely undetected by a conventional envelope cross-correlation method. Exploratory perusal of array stacks indicates a complex pattern of tremor activity. Oftentimes, multiple lively tremor sources appear to be active simultaneously. The AofA is providing a high-resolution probe of seismic activity during both ETS, and inter-ETS time period.
Session:Combining Geodetic and Seismic Measurements
Presenter   Glowacka, Ewa
Schedule   Fri PM / Poster
Room   Ballroom B
Coseismic and Aseismic Anomalies Recorded by Geotechnical Instruments in the Cerro Prieto Pull Apart Basin, Baja California, México.
GLOWACKA, E., CICESE, Ensenada, Baja California, Mexico, glowacka@cicese.mx; SARYCHIKHINA, O., CICESE, Ensenada, Baja California, Mexico, osarytch@cicese.mx; VAZQUEZ, R., CICESE, Ensenada, Baja California, Mexico, rvazquez@cicese.mx; VIDAL, A., CICESE, Ensenada, Baja California, Mexico, vidalv@cicese.mx; AGUADO GUZMAN, C., Instituto Tecnológico de Ciudad Madero, Ciuadad Madero, Tamaulipas, Mexico, ; LOPEZ HERNANDEZ, M., UAG, Guerrero, Mexico, ; FARFAN, F., CICESE, Ensenada, B C, Mexico, ; DIAZ DE COSSIO BATANI, G., CICESE, Ensenada, B C, Mexico,
The Cerro Prieto Pull-Apart Basin (CPB) is located in the southern part of the Salton Trough, in the boundary between the Pacific and North American plates. Since 1996, CICESE has been operating a network of geotechnical instrument for continuous recording of deformation related to tectonic (seismic, aseismic and interseismic) phenomena, as well as anthropogenic deformation caused by the deep fluid extraction at the Cerro Prieto Geothermal Field. The instruments are installed along the faults that limit the CPB. To date, the network includes 3 crackmeters, 6 tiltmeters (two in 5 meters deep boreholes), and 5 piezometers installed in wells at depths of 150 m and 500 m, in the shallow aquifer. All instruments have sampling intervals in the 1 to 20 minutes range. Since the network installation 3 important earthquakes were recorded by the geotechnical instruments: the May 24, 2006 Mw=5.4, normal mechanism, earthquake occurred on the Morelia fault, which limits CPB from the NW, the December 30, 2009, Mw=5.8, strike-slip earthquake on the NE limit of the CPB, and the April 4, 2010, Mw=7.2 El Mayor-Cucapah earthquake, with epicenter outside the basin, but close (8 to 15 km) to the installed instruments. Coseismic step-like groundwater level changes ranging from 0.01 to 7.0 meters were recorded at wells in the CPB, equivalent to coseismic volumetric strain field, in the depth of the piezometers, of the order of 10-7 – 10-5. Since the network installation, dozens of slip aseismic events were recorded on the instruments installed along the Saltillo fault. The episodic fault slip appears mainly as slip-predictable, aseismic normal slip, with amplitudes of 1-3 cm and durations of 1-3 days and often is related to few centimeters groundwater level changes. In presented work we use volumetric strain efficiency, (calculated for recorded earthquakes), in order to obtain the volumetric strain caused by episodic slip and to model the episodic slip phenomena.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Brown, Justin
Schedule   Thu 9:45 AM / Oral
Room   Ballroom D
Factors Influencing Tremor Occurrence in Subduction Zones
BROWN, J. R., Stanford University, Stanford, CA, jrbrown5@stanford.edu; BEROZA, G. C., Stanford University, Stanford, CA, beroza@stanford.edu
Tectonic tremor from multiple circum-Pacific subduction zones has been shown to consist of repeating low frequency earthquakes on the plate interface. Tremor/LFE occurrence in some areas exhibits episodic behavior down-dip of previous great mega-thrust earthquakes suggesting that the tremor may delimit the lower edges of large earthquake rupture. We investigate where and why tremor does (and does not) occur. We compare observations of LFE locations in five subduction zones: southwest Japan, Cascadia, Alaska-Aleutian Arc, Costa Rica and Mexico. We compare the LFE location patterns among the five areas with subduction parameters such as incoming sediment thickness, plate age, convergence rate and temperature. A preliminary conclusion is that temperature exerts a strong influence on LFE depth; warmer subduction zones (e.g. southwest Japan, Cascadia) experience tremor activity around 30-40 km depth, whereas cooler subduction zones (e.g. the Alaska-Aleutian Arc) experience tremor between 45-55 km depth. In addition, sediment thickness seems to play little to no role in tremor/LFE depths. This may be attributable to the amount of shear and chemical alterations that occur in the primary seismogenic zone up-dip from the tremor zone.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Langbein, John
Schedule   Thu AM / Poster
Room   Ballroom B
Estimation of Deformation Rates Across the New Madrid Seismic Zone Based upon GPS Measurements, 2000 – 2010
LANGBEIN, J., U.S. Geological Survey, Menlo Park, CA, langbein@usgs.gov; SVARC, J., U.S. Geological Survey, Menlo Park, CA, jsvarc@usgs.gov; MURRAY-MORALEDA, J. R., U.S. Geological Survey, Menlo Park, CA, jrmurray@usgs.gov
Over the past 10 years, the University of Memphis, National Geodetic Survey, and NOAA's Forecast Research Branch have had GPS receivers continuously recording at approximately 25 sites located in a region that spans the New Madrid Seismic Zone (NMSZ). Data from these instruments are processed into daily estimates of position, from which the rates of deformation at each site are calculated. From the spatial distribution of these rates, the total deformation across the NMSZ is estimated. Importantly, these rates can be used to test models of physical processes that might explain the source of historical and current earthquakes, thus providing input to the estimate of the seismic hazard in this region. We have reprocessed the data from the GPS sites that have been continuously operating since 2000 using the GIPSY-OASIS software with point-positioning and ambiguity resolution. Daily estimates of position, relative to the North American reference frame, are further refined by regional filtering which removes spatially coherent fluctuations from the time-series of the position estimates. Before estimating site velocities and parameters of an error model of temporal correlations, spurious measurements and offsets in each time series of position estimates are identified and removed. The analysis from our processing of the GPS data can be compared with the analysis by Calais and others (http://web.ics.purdue.edu/~ecalais/projects/noam/nmsz/ts) using different techniques. Since previous analyses provided in the literature indicate that the deformation rates across the NMSZ may or may not be statistically significant, it is best to use differing techniques to obtain robust estimates of velocities and their uncertainties.
Session:Seismotectonics and Hazards of Active Margins in the Circum-Caribbean Sea and Eastern Pacific Ocean
Presenter   Tsang, Rebecca
Schedule   Wed 11:45 AM / Oral
Room   Ballroom D
Towards Development of a Long Rupture History of the Imperial Fault in Mesquite Basin, Imperial Valley, Southern California
TSANG, R. Y., San Diego State University, San Diego, CA, tsang.y.rebecca@gmail.com; ROCKWELL, T. K., San Diego State University, San Diego, CA, trockwell@geology.sdsu.edu; MELTZNER, A. J., Earth Observatory of Singapore, Nanyang Technological University, Singapore, meltzner@ntu.edu.sg; FIGUEIREDO, P. M., IDL / FCUL - Geology Department Lisbon University, Lisbon, Portugal, pmfigueiredo@fc.ul.pt
We excavated new trenches across the northern Imperial Fault at the Dogwood site in Mesquite Basin to extend the record of earthquakes that have produced surface rupture there. In our earlier work, we resolved timing and displacement for the six most recent surface ruptures, all of which have occurred in the past 500 years. In our current work, we have refined the chronology of these events and extended the paleoseismic record back to nearly 1200 years, during which Lake Cahuilla intermittently filled the Salton depression, although the ages of the three earliest identified ruptures are not yet well resolved. The site chronology was refined using a combination of locally determined radiocarbon ages and a regionally developed lake chronology. The two most recent events are the historically known 1979 and 1940 surface ruptures, both of which were mapped through the site after each respective earthquake. Event E3 occurred about AD 1710 whereas E4 occurred only decades before, between about AD 1660 and 1700. Events E5 through E8 occurred in the period between about AD 1280 and 1640, which taken with the youngest events, suggests an average recurrence interval of about 100 years (7 intervals in 700 years), although with a potentially large CV. The ages of the earliest three identified events, E9, E10, and E11, are dependent on the correlations to the regional lake stratigraphy and require further dating. Our current interpretation places all three of these events after AD 850, although an alternative correlation suggests that they could have occurred after AD 950; neither interpretation significantly changes the average recurrence interval. These observations indicate that some earthquakes on the northern Imperial Fault have occurred in clusters (pairs) and that recurrence has been irregular.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Mooney, Walter
Schedule   Wed 11:00 AM / Oral
Room   Ballroom C
A Review of the Lithospheric Structure of the Greater New Madrid Seismic Zone: Implications for Seismic ActivityM
MOONEY, W. D., USGS, Menlo Park, CA, mooney@usgs.gov
Recent studies indicate that specific characteristics of the lithospheric structure of the greater New Madrid Seismic Zone (NMSZ) are well correlated with seismic activity. Crustal anomalies, both shallow and deep, have been hypothesized to correlate with zones of concentrated seismic moment release. Such anomalies include the features of a paleo-rift and upper-crustal zones postulated to contain fluid-filled cracks. Numerous seismological studies have been undertaken in recent years, and these reveal that the crust beneath the Mississippi embayment is relatively thick (40-50 km), and has a high average crustal velocity (6.4-6.6 km/s) that is indicative of a dense, mafic lower crustal composition. The 15-km thick, high-velocity (>7.0 km/s) lower crust has been termed a rift pillow and is one of the most prominent and unique features of the NMSZ. Shallow, high-resolution seismic reflection surveys image numerous post-late Cretaceous faults and folds, some of which are coincident with mapped faults. Local earthquake tomography inversions suggest that the upper crust of the NMSZ is characterized by localized fluid-filled cracks. This hypothesis has recently found support in the discovery of the local presence of anomalously low Vp/Vs ratios associated with several active zones of seismicity. I compare the lithospheric thickness and calculated lithospheric temperatures in the central US with locations and magnitudes of crustal earthquakes. Greater integrative lithospheric strength correlates with lower rates of seismicity and a lower value of Mmax. I also find a strong anti-correlation of mantle lithospheric shear-wave velocity versus the number of crustal earthquakes with moment magnitude >5. Higher shear-wave velocity (a proxy for temperature) at 100 km depth corresponds to relatively fewer crustal earthquakes. Thus, regional geophysical data from the central US shows that strong, cold lithosphere has relatively fewer crustal earthquakes and a lower value of Mmax.
Session:Seismic Sources and Parameters
Presenter   Pujol, Jose
Schedule   Wed 5:30 PM / Oral
Room   Ballroom E
Angles between fault planes and between focal mechanisms of earthquakes
PUJOL, J., University of Memphis, Memphis, TN, jpujol@memphis.edu
The focal mechanism of an earthquake can be represented by a rotation matrix with the strike, dip, and slip playing the role of Euler angles. This matrix rotates the slip and normal vectors for a special case into the corresponding vectors for the given earthquake. The matrix can be expressed in terms of a rotation axis and angle, which in turn allows the determination of the quaternion associated with the rotation. Quaternions can be considered elements in a 4-D space with the usual scalar product. Therefore, given two quaternions, it is possible to compute the angle between them. This angle, say A, is taken as the angle between the fault planes or focal mechanisms and satisfies cos(A) = cos(B/2)*cos(C/2) + sin(B/2)*sin(C/2)*cos(D), where B and C are the two rotation angles and D is the angle between the rotation axes. Some general results were derived. Two of them are given here. First, the angle between a fault plane and the auxiliary plane is equal to 90º. Second, if two faults have the same strike and dip and their slips differ by 180º, the angle between the two focal mechanisms (represented by the p, b, and t vectors) is equal to 90º. In this case the p and t axes are interchanged. The 90º angle also occurs for other combinations of strike, dip, and slip. The relations with the angles determined by other authors have also been derived. Kagan (GJI, 1991) used quaternions, but with a completely different formulation. In particular, the angle determined from the product of one of the quaternions and the inverse of the other is equal to twice the angle determined here. When the angle is determined from the trace of the product of one of the rotation matrices and the transpose of the other (Kagan, GJI, 2007; Arnold and Townend, GJI, 2007), half of that angle is equal to either the angle determined here, or to its supplement.
Session:Seismic Sources and Parameters
Presenter   Pujol, Jose
Schedule   Wed 5:00 PM / Oral
Room   Ballroom E
The variation of travel time for seismic rays with a free end pointand application to the problem of earthquake location
GOLDSTEIN, G. R., University of Memphis, Memphis, TN, ggoldste@memphis.edu; PUJOL, J., University of Memphis, Memphis, TN,
The standard earthquake location techniques are based on the iterative solution of a linearized problem that requires the computation of partial derivatives of travel time with respect to the hypocentral coordinates. A standard derivation of the corresponding equations is based on a variational principle applied to a ray with fixed end points (i.e., the recording station and the hypocenter). However, this derivation ignores the fact that the hypocentral location is unknown, which means that the variational analysis should be applied to a ray with a free end point (corresponding to the hypocenter). When this is done it is found that the travel time variation has three terms: (a) a term that leads to the standard Euler equations for a ray with its two end points fixed, and (b) two additional terms. Interestingly, these two terms cancel whenever the seismic rays have wavefronts that satisfy the eikonal equation (which occurs so long as the WKBJ or high frequency approximation holds). In particular this shows that the equations currently used to compute the partial derivatives are correct, although the derivation leading to them was not in the high frequency case. In general, this cancellation does not occur for waves not satisfying the WKBJ approximation.
Session:Earthquake Debates: Should Earthquake Early Warning be Implemented?
Presenter   Malone, Steve
Schedule   Thu 4:30 PM / Oral
Room   Ballroom D
Developing Earthquake Early Warning in the US is Currently a Waste of Time and Money
MALONE, S. D., University of Washington, Seattle, WA, steve@ess.washington.edu; VIDALE, J. E., University of Washington, Seattle, WA, vidale@uw.edu
An earthquake early warning (EEW) system provides advance warning of strong shaking after an earthquake has been detected but before the strongest shaking arrives. EEW systems gain power from dense instrumentation in the earthquake source region, accurate and flexible source characterization, and need rapid and reliable data transmission and computer algorithms. EEW systems must be well connected with end users. EEW systems are now either operational or are being implemented in several other countries, and the USGS is currently supporting developments in California.Earthquake Early Warning seems to be a solution to a problem that no one is asking to be solved. It is hard to find evidence of emergency managers or civil authorities asking for or even being very interested in EEW. Other places in the world where EEW has been implemented there are no cases where it has proven to be truly socially useful even where the technology worked. The technology currently exists to generate warnings minutes before strong shaking arrives where the geography is ideal (subduction zones far from major cities), yet in the US all of the effort is being made in California where the major faults run near or through the major cities. The technology of usefully communicating an early warning alarm to a significant population that could benefit does not yet exist in the US. Educating (and re-educating) a population to properly deal with alarms (and false alarms) is a much bigger and more costly problem than the seismological problem. Early warning alarms for other natural hazards where warning times can be hours or even days have often been ignored or very poorly used by society (Hurricane Katrina). At best, trying to implement EEW technology now is way ahead of its time. At worst, it will cost lives by taking resources away from proven earthquake hazard mitigation efforts. Consequently, EEW's development in the US should not be a major goal of seismology.
Session:Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Presenter   Liu, Mian
Schedule   Thu 1:30 PM / Oral
Room   Ballroom C
2000 years of migrating earthquakes in North China: Fault coupling and interaction in midcontinents
LIU, M., University of Missouri, Columbia, MO, lium@missouri.edu; STEIN, S., Northwestern University, Evanston, IL, seth@earth.northwestern.edu; WANG, H., China Earthquake Administration, Beijing, China,
Intracontinental earthquakes have far more irregular occurrence in time and space than those at plate boundaries. This is illustrated by the 2000-year record from North China, which shows migration of large earthquakes between fault systems spread over a large region. The spatial migration of these earthquakes, however, is not entirely random, because the seismic energy release between fault systems are complementary, indicating that these systems are mechanically coupled. We propose a simple conceptual model for intracontinental earthquakes, in which slow tectonic loading in midcontinents is accommodated collectively by a complex system of interacting faults, each of which can be active for a short period after long dormancy. The resulting large earthquakes are episodic and spatially migrating. Further studies of fault coupling and interaction in midcontinents are needed to improve forecasting and hazard assessment of intracontinental earthquakes.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Talwani, Pradeep
Schedule   Thu 8:30 AM / Oral
Room   Ballroom C
A Testable Model for Intraplate Earthquakes
TALWANI, P., University of South Carolina, Columbia, SC, pradeep@sc.edu
Globally, more than 98% of the total seismic moment release associated with intraplate earthquakes (IPE) occurs in former rifts and taphrogens (Schulte and Mooney, 2001). The seismicity occurs at stress concentrators in both shallow and deeper crust in response to the ambient compressional stress field (Gangopadhyay and Talwani, 2003). At many locations of IPE, the stress field is further modified by local stress perturbations (e.g. due to glacial rebound, sedimentary deposition etc., Talwani and Rajendran, 1990). Weakening agents, such as the presence of fluids at hypocentral depths further influence the seismogenesis of IPE. Mooney and Fujita(2010) have shown that these rifted basins are associated with a weaker lower crust, mappable by S-wave seismic tomography. Several global case histories exemplify these observations. Modeling results have shown that when rifted sedimentary basins which had been formed under extension, with a priori weaknesses, are inverted under compression, the results are weak conjugate and boundary faults with up-welled lower crust. These characteristic features of stress inversion are associated with local (~10s km x10s km surface area) elevated strain rates. These observations and modeling results suggest the following testable model. Major IPE occur in reactivated rifted basins, with conjugate and boundary faults and an up-welled lower crust. (The precise geometry and seismic potential of each site depends on its tectonic history and geometry after stress inversion). These features are sites of LOCAL stress concentrations and elevated strain rates, and potential IPE.To test this model and to predict potential locations of IPE, S-wave tomography can be used to define the weaker lower crust associated with rifted basins, and dense, continuous GPS observations can be used to identify LOCAL pockets of elevated strain rates; and seismicity and geophysical observations can be used to identify stress concentrators and locations of IPE.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Rawles, Chris
Schedule   Thu AM / Poster
Room   Ballroom B
Variable Apparent Stress Scaling From Coda Envelopes for Southern California Sequences
MAYEDA, K., Weston Geophysical Corporation, Lexington, MA, kmayeda@yahoo.com; RAWLES, C., UC Berkeley, Berkeley Seismological Laboratory, Berkeley, CA, crawles@gmail.com; MALAGNINI, L., INGV, Rome, Italy, malagnini@ingv.it; YOO, S. H., UC Berkeley, Berkeley Seismological Laboratory, Berkeley, CA, hoonthhoonth@gmail.com
The study of earthquake source scaling continues to be a topic of much debate because it has profound implications for a variety of sub-disciplines within seismology, ranging from earthquake hazard prediction to nuclear explosion monitoring endeavors. Often times studies using different methodologies considering the same dataset provide different results and the merging of studies often provides more questions than answers. This study considers five southern California sequences using the coda ratio methodology that has been shown to provide the lowest variance in source amplitude ratios, corner frequency, and apparent stress estimates to date. Though we find little evidence of a scaling break for the 2004 Mw 6.0 Parkfield sequence, the other four sequences: Baja, Hector Mine, Northridge, and San Simeon all show a clear break near Mw 5.5, consistent with many other large magnitude sequences globally using the same methodology. We will compare these recent results with previous studies and try to relate them to the degree of tectonic activity and focal mechanism.
Session:Creative Wavefield Recording and Analysis
Presenter   Abbott, Robert
Schedule   Fri PM / Poster
Room   Ballroom B
Development of a New Six-Degree-of-Freedom Seismic Sensor Using Atom Interferometry
BIEDERMANN, G., Sandia National Laboratories, Albuquerque, NM, gbieder@sandia.gov; ABBOTT, R. E., Sandia National Laboratories, Albuquerque, NM, reabbot@sandia.gov
Atom interferometers have the potential to be exceptional broadband seismic sensors in both translational and rotational degrees of freedom. The demonstrated performance of this technology rivals the best ring-laser gyroscopes and falling corner-cube gravimeters. However, compact and field-worthy manifestations of atom interferometers remain elusive using standard approaches. Furthermore, with current bandwidth limited to a few Hz, broadband seismic applications are yet to be realized. We propose to explore a short time-of-flight approach which we anticipate will reduce sensor size, improve ruggedness, and increase bandwidth by two orders of magnitude.
Session:Archeoseismology: Learning about Ancient Earthquakes from the Archeological Record
Presenter   Allison, Alivia
Schedule   Fri 9:00 AM / Oral
Room   Ballroom D
New Excavations at Early Islamic Ayla on the Gulf Coast of Aqaba Along the Southern Dead Sea Transform, Jordan
ALLISON, A. J., University of Missouri - Kansas City, Kansas City, MO, ajad36@mail.umkc.edu; NIEMI, T. M., University of Missouri - Kansas City, Kansas City, MO, niemit@umkc.edu
Aqaba, Jordan is situated at the northern end of the Gulf of Aqaba along the southern portion of the Dead Sea Transform (DST). Based on both historical accounts and archaeological excavations, it is clear that earthquakes have played a substantial role in the history of the region. The early Islamic city of Ayla was likely founded around 650 A.D., suffered some damage in the 8th Century, likely in the 749 or 757 earthquakes, and saw extensive reconstruction around the mid-8th C. or Abbasid period (Whitcomb, 1994). Among other evidence of earthquake destruction at the Islamic city of Ayla is the leaning city Sea wall. A portion of the city wall leans toward the Gulf and was buttressed in antiquity. In February 2009, we excavated two 2 x 3 m trenches at this site: one which included the visible western edge of the revetment, and the other trench sectioned the revetment wall itself in order to obtain datable material from within and below the wall. Stratified pottery collections from our excavation of the city wall buttress strongly suggest a date for revetment construction in the early 11th Century. Considering that the most recent pottery from sealed loci inside the buttress wall is late Abbasid – Fatimid, as well as the absence of handmade pottery often found in the abandonment phases at Ayla, the buttress was likely constructed after liquefaction damage from an earthquake that pre-dates the large 1068 A.D. seismic event that destroyed the city. The devastation to Ayla in 1068 was so significant that it is said to have killed all but 12 residents out fishing on the Gulf at the time. Although the DST fault trace has not been identified at the site of Ayla, damage sustained in the ancient city from potential distant source earthquakes was repaired in antiquity. Significantly, these data document a long period of quiescence since the last phase of intense earthquake activity along the southern DST, and highlight the elevated potential earthquake hazard in the region.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Myers, Stephen
Schedule   Fri 2:00 PM / Oral
Room   Ballroom E
Simultaneous global event relocation and assessment of arrival time data using Bayesloc
MYERS, S. C., Lawrence Livermore National Lab, Livermore, CA, smyers@llnl.gov; JOHANNESSON, G., Lawrence Livermore National Lab, Livermore, CA, ; SIMMONS, N. A., Lawrence Livermore National Lab, Livermore, CA,
We have extended the Bayesloc seismic multiple-event location algorithm for application to global arrival time data sets. Bayesloc is a formulation of the joint probability distribution spanning multiple-event location parameters, including hypocenters, travel time corrections, pick precision, and phase labels. Stochastic priors may be used to constrain any of the Bayesloc parameters. Markov Chain Monte Carlo (MCMC) sampling is used to draw samples from the joint probability distribution, and the posteriori samples are summarized to infer conventional location parameters such as the hypocenter. The data set consists of a ~1-degree lateral sampling of events with the most P- and Pn-wave arrival time data, as well as events with outstanding azimuthal coverage. Sampling is performed in predefined depth ranges to capture subduction seismicity. We also add all well-recorded events for which epicenter accuracy is known to 5 km or better. Over 3.5 million arrivals from over 13 thousands events comprise the data set. For testing purposes, we do not include prior constraints on epicenters with known location, and we find that the median difference between the relocated epicenters and the known location is 4.8 km. Less than 1% of the arrival time data are determined to be erroneous, and thus discarded. Approximately 3% of phases are relabeled with posteriori confidence greater than 0.9. Bayesloc relocation and data processing results in a reduction of travel time residual standard deviation with respect to the ak135 model from 1.87 s to 1.35 s. Last, tests of travel time residuals for nearly reciprocal paths suggest that the Bayesloc processing improves data set consistency, which is important for use in tomographic studies. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Adnan, Azlan
Schedule   Thu 3:45 PM / Oral
Room   Ballroom E
New Seismic Hazard Map of Peninsular Malaysia Using Next Generation Attenuations
ADNAN, A., University of Technology Malaysia, Skudai, Johor, Malaysia, azelan_fka_utm@yahoo.com; MELDI, S., University of Technology malaysia, Skudai, Johor, Malaysia, meldisht@hotmail.com; HENDRIYAWAN, , Instittute of Technology Bandung, Bandung, West Jawa, Indonesia, h3ndri91@yahoo.com; MASYHUR, I., Institute of Technology Bandung, Bandung, West Jawa, Indonesia, masyhur.irsyam@yahoo.co.id
The seismic hazard map of Peninsular Malaysia using Next Generation Attenuations (NGA) in the probabilistic approach is presented. The analysis covers the development of seismotectonic model based on new available historical earthquakes data, new methods in determining seismic hazard parameters, and new selection of appropriate attenuation relationships for Peninsular Malaysia region. The combined catalog covers an area from 90E to 125E longitude and 10S to 10N latitude. The total numbers of relevant earthquakes, after the filtering process, are 7359. The catalog dated from 1 May 1900 to 31 December 2009. The earthquake source model includes the subduction, the fault source, and background source zones. Logic tree method is performed in the analysis to take into account the epistemic uncertainty by explicitly including alternative interpretations, models, and parameters that are weighted in the analysis according to their probability of being correct. The hazard calculations were then performed for several combinations of attenuation functions, seismic hazard parameters, and maximum magnitudes. Two hazard maps representing 10% and 2% probability of exceedance (PE) in 50 years ground motions for Peninsular Malaysia were developed which result in 0.11g and 0.25g at the west coast and 0.027g and 0.05g (east coast), respectively. The deaggregation analysis conducted for Kuala Lumpur, in the west coast, showed the mean contribution of earthquake intensity of Mw=8.0 at R=280km and M=8.2 and R=230km for 500 years and 2,500 years return period, slightly increased by 5% from the previous hazard map (2005).
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Walter, William
Schedule   Thu 1:30 PM / Oral
Room   Room 204/205
Investigating Earthquake Scaling Using Spectral Ratios and Simple Earthquake Models
WALTER, W. R., Lawrence Livermore National Laboratory, Livermore, CA, walter5@llnl.gov; GOK, R., Lawrence Livemore National Laboratory, Livermore, CA, gok1@llnl.gov; MAYEDA, K., 2Weston Geophysical Corporation, Lexington, MA, kmayeda@yahoo.com; MALAGNINI, L., Istituto Nazionale di Geofisica e Vulcanolgia, Roma, Italy, malagna@ingv.it
Earthquakes span many orders of magnitude in size, and quantifying how they scale can reveal insights in the nature of how they initiate, grow and stop. To study earthquake source characteristics it is necessary to first account for and remove other (e.g. path and site) effects. A straightforward and longstanding approach is to use a nearby small event as an empirical Green function (EGF) in the analysis of a larger earthquake. Traditionally the two events needed to be very similar in terms of epicenter and mechanism, but the development of the coda spectral ratio methodology (Mayeda et al. 2007) allows a much greater number of events to be used for EGF analysis while providing a lower variance estimate of the amplitude ratio between events. In the frequency domain the EGF is simply a spectral ratio, which normally has a sigmoid shape with the low frequency level related to the ratio of the moments, the inflection points are at the corner frequencies of the large and small event and the high frequency level is function of both of their moments and corner frequencies.We use a simple single corner frequency spectral model with self- and non-self-similar scaling to model many coda spectral ratios, individually and simultaneously, to map out the source parameters and their uncertainties. Having a source model allows a better understanding of the uncertainties for particular ratios in terms of bandwidth and data quality. The model shows the critical value of having independent constraints on the moments of the events, to reduce the source parameter uncertainties. These may be obtained from longer period waveform moment tensor modeling for example. We show the results do not depend strongly on the shape of the source spectra except in regard to the rate of high frequency falloff above the corner frequency.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Koketsu, Kazuki
Schedule   Fri 2:15 PM / Oral
Room   Ballroom D
Unanticipated Exceptional Ground Motions at a Nuclear Power Plant during the 2007 Chuetsu-Oki, Japan, Earthquake
KOKETSU, K., Earthquake Research Institute, University of Tokyo, Tokyo, Japan, koketsu@eri.u-tokyo.ac.jp; TODA, K., Earthquake Research Institute, University of Tokyo, Tokyo, Japan, kj-toda@eri.u-tokyo.ac.jp; MIYAKE, H., Earthquake Research Institute, University of Tokyo, Tokyo, Japan, hiroe@eri.u-tokyo.ac.jp
The 2007 Chuetsu-oki, Japan, earthquake occurred on July 16 with a moment magnitude (Mw) of 6.6. This event is significant as the world’s first major earthquake upon a source fault that extends beneath a nuclear power plant. Seven reactors within the Kashiwazaki-Kariwa nuclear power plant experienced much stronger ground motions and longer periods than those anticipated at the time of plant design. In addition, such exceptional ground motions (Anderson, 2010) could not be anticipated from the standard equation for siting of nuclear power plants in Japan. It is therefore important for the seismic safety of all nuclear power plants that the reasons for these underestimates in hazard assessment are investigated by analyzing the observed ground motions. Since the source effects, that are the rupture directivity effect and combination of radiation pattern and high stress drop, have been investigated in detail by Miyake et al. (2010), we next investigated the path effects by modeling a velocity structure and simulating ground motions. We used the Japan Integrated Velocity Structure Model (Koketsu et al., 2008) and the 2008 JNES model for constructing an initial model, and revised it by comparing observed and synthetic seismograms from an aftershock of the Chuetsu-oki earthquake. We then carried out simulations of ground motions at the plant during the mainshock. Preliminary results indicate that the obtained velocity structure can double the amplitudes and response spectra, compared with those by a typical velocity structure for the standard equation for siting of nuclear power plants in Japan.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Hao, Yanjun
Schedule   Thu PM / Poster
Room   Ballroom B
Characterizing The Geometry and History of Deformation of The Meeman-Shelby Fault (Central U.S.)
HAO, Y., CERI, Memphis, TN, yhao@memphis.edu; MAGNANI, M. B., CERI, Memphis, TN, mmagnani@memphis.edu; GUO, L., CERI, Memphis, TN, lguo2@memphis.edu; ODUM, J. K., USGS, Geologic Hazards Team, Golden, CO, odum@usgs.gov; WORLEY, D. M., USGS, CRGHT, Golden, CO, worley@usgs.gov
Despite continuing studies in geodesy, seismology and paleoseismology in the Central U.S., there remains a paradox regarding the documented series of relatively large seismic events in the New Madrid Seismic Zone (NMSZ) and the apparent low rates of deformation measured in the area. A promising hypothesis proposed to reconcile the clashing observation is that deformation may be focused in different areas at different times, and that the present NMSZ seismicity might not reflect the long-term behavior of the fault system in the Central U.S.In the summer of 2008 a high-resolution marine seismic reflection profile acquired along the Mississippi River imaged a 40 km-long fault ~10km north of Memphis, TN. The fault, named the Meeman-Shelby Fault (MSF), strikes N25E and offsets/folds the unconsolidated sediments from the top of the Paleozoic to the base of the Quaternary alluvium, suggesting recent tectonic activity.In order to image the onshore continuation of the fault in the fall of 2010 an additional 10 km-long high-resolution seismic reflection profile was acquired on land, across the segment of the fault between two river crossings. The profile was acquired using a Vibroseis seismic source (40-150 Hz, 12 s long linear sweep), 144 channels, 5 m receiver interval, 10 m source interval and 5 m minimum offset to ensure recording from shallow reflectors. Listening time was 14 s for a total of 2 s correlated record length.The survey acquired high quality data. Clear reflected arrivals are visible in raw shot gathers from shallow depth (~50-100 ms), to ~1.5 s. Sharp reflections at 800 ms and 1.3s profiles corresponding to the top of the Cretaceous and the top of the Paleozoic sequences are traceable throughout the profile. Seismic data processing steps include: 1) removal of surface waves by zeroing the arrival zone, 2) frequency filtering, 3) predictive deconvolution, 4) velocity analysis and NMO correction, and 5) CDP sorting and stacking.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Rhoades, David
Schedule   Fri 4:15 PM / Oral
Room   Ballroom E
A Testable Earthquake Likelihood Model Based on Proximity to Mapped Faults and Previous Earthquakes
RHOADES, D. A., GNS Science, Lower Hutt, New Zealand, d.rhoades@gns.cri.nz; STIRLING, M. W., GNS Science, Lower Hutt, New Zealand, m.stirling@gns.cri.nz
We propose a new long-term earthquake likelihood model which makes use of data on both mapped faults and past earthquakes, but does not invoke the concepts of fault segments or characteristic earthquakes. This model has two components, one based on proximity to past earthquakes, taking into account the magnitude of each, and another based on proximity to mapped faults, taking into account the slip-rate of each. A tapered Gutenberg-Richter law is invoked for earthquake magnitudes and an inverse power law for the diminution of earthquake rate density with distance from past earthquakes and mapped faults. The parameters of each component are optimised using a target catalogue, and the rate density of the combined model is estimated as an optimal linear combination of the two components. The model has been applied to the New Zealand region using the active fault database and the earthquake catalogue since 1964. However, it can be readily applied to any region for which a database of active faults and associated slip rates is available. The model is suitable for evaluation by the testing centers of the Collaboratory for the Study of Earthquake Predictability, in which its performance can be compared with other long-term models, including those based on standard probabilistic seismic hazard analysis.
Session:Earthquake Debates: Should Earthquake Early Warning be Implemented?
Presenter   Vidale, John
Schedule   Thu 4:00 PM / Oral
Room   Ballroom D
Earthquake Early Warning in the US is inevitable and imminent
VIDALE, J. E., U of Washington, Seattle, WA, vidale@uw.edu; MALONE, S. D., U of Washington, Seattle, WA, steve@ess.washington.edu
An earthquake early warning (EEW) system provides advance warning of strong shaking after an earthquake has been detected but before the strongest shaking arrives. EEW systems gain power from dense instrumentation in the earthquake source region, accurate and flexible source characterization, a good understanding of the shallow geology for accurate prognostication of the seismic waves, and need rapid and reliable data transmission and computer algorithms. The EEW system must be connected with users of the warning ahead of time. EEW systems are now either operational or are being implemented in several other countries, and the USGS is currently supporting the development of algorithms and tests in California.The benefits of EEW are not yet easy to quantify, however the simplicity of providing basic EEW alarms means that EEW is definitely coming, and has already come in some forms. I'd argue that high-performance EEW for the US west coast is at most 10 years away, and once it is here, no one will dispute its value for dollar. Key advantages are (1) the psychological reassurance that the populace does not need to interpret every bump in the night as potentially apocalyptic, (2) some of the myriad tactical uses of EEW - stopping surgery, trains, airport take-offs and landing, closing bridges, opening critical doors, warning school kids - will prove valuable, and (3) EEW systems provide a firm basis for all earthquake monitoring systems - fast, accurate, and reliable - and so reinforce all earthquake monitoring efforts. In particular, the likelihood that major earthquakes will disrupt communications and operations means that the instant global data delivery through an EEW is a critical feature in assuring responsive earthquake monitoring and the performance of back-up systems.It's only a matter of a short time, and whether existing seismic network or new organizations step into the current vacuum.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Prejean, Stephanie
Schedule   Wed 2:15 PM / Oral
Room   Ballroom D
The 2008 Earthquake Swarm at Trident and Novarupta Volcanoes: A Case of Fluid Triggered Seismicity?
PREJEAN, S., USGS Alaska Volcano Observatory, Anchorage, AK, sprejean@usgs.gov; MURPHY, R., University of Wisconsin, Madison, Department of Geoscience, Madison, WI, rmurphy@geology.wisc.edu; THURBER, C., University of Wisconsin, Madison, Department of Geoscience, Madison, WI, thurber@geology.wisc.edu; MCNUTT, S., University of Alaska, Fairbanks, Geophysical Institute, Fairbanks, AK, steve@giseis.alaska.edu; STIHLER, S., University of Alaska, Fairbanks, Geophysical Institute, Madison, WI, scott@giseis.alaska.edu; SYRACUSE, E., University of Wisconsin, Madison, Department of Geoscience, Madison, WI, syracuse@geology.wisc.edu
In 2008 the region of Novarupta and Trident volcanoes (NT) in the Katmai volcanic cluster, Alaska, experienced a vigorous earthquake swarm. A series of deep (>25 km) long-period earthquakes located beneath the shallow volume of seismically active crust accompanied the swarm. We captured the latter half of the swarm with a focused array of 10 broadband seismometers. As this temporary network was located within a larger-scale permanent network of 20 stations, seismic coverage of the swarm was exceptional for remote volcanoes. Using the combined datasets we computed ~130 high-quality first motion fault plane solutions for brittle failure earthquakes associated with the swarm. Although a small percentage of events do not appear to be consistent with a double-couple source, the majority have well constrained double-couple solutions. Computed fault plane solutions in the NT region are highly diverse, unlike those of some neighboring Katmai volcanoes. For example solutions from Mt. Martin, 10 km southwest of NT, show almost exclusively normal faulting. Most NT area earthquakes are located between Trident’s summit and the Novarupta vent in a NE-SW elongated cluster which borders a low velocity and high attenuation anomaly to the SE. Fault plane solutions suggest that this area is a normal to strike-slip faulting environment where the vertical effective stress and most compressive horizontal effective stress are similar in magnitude. Strikes of inferred normal faults roughly parallel the NE-SW trend of the relocated hypocenter cluster. Based on these observations, we envision that earthquakes in the 2008 swarm occurred on a network of normal and strike-slip faults in a high-pore-pressure volume of crust that bounds a region of shallow magma storage. High focal mechanism diversity in the swarm and the association with deep long-period events suggest that the earthquakes were triggered by renewed fluid movement from depth.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Wu, Chunquan
Schedule   Wed AM / Poster
Room   Ballroom B
Remote Triggering of moderate earthquakes in East Asia
WU, C., School of Earth & Atm. Sci, Georgia Institute of Technology, Atlanta, GA, chunquanwu@gatech.edu; PENG, Z., School of Earth & Atm. Sci, Georgia Institute of Technology, Atlanta, GA, zpeng.seismo@gmail.com
Recent studies have shown that large earthquakes are capable of triggering microearthquakes and deep “non-volcanic” tremor at regional and teleseismic distances. These types of dynamic triggering are found not only at active plate-boundary faults, but also within relatively stable intraplate regions. However, it is still not clear what are the necessary conditions and most plausible physical models for dynamic triggering, and whether the dynamically triggered microearthquakes could lead to large (M>5) events. Here we perform a systematic survey of the seismicity rate changes in east Asia following several large earthquakes in this region, including 2004 M9.2 Sumatra, 2005 Mw8.7 Nias, and 2008 Mw7.9 Wenchuan earthquakes. We use regional earthquake catalogs from 2001 to 2008 for Continental China, and from 1997 to 2009 for Taiwan. We select those M>5 earthquake within 6 months of each major event, and focus on the seismicity rate changes in the source regions of the selected M>5 events. Our preliminary results indicate observable seismic rate increases in the source regions of several M>5 events in southwestern China, and along the east coast of central Taiwan after the 2004 Sumatra earthquake. Our ongoing efforts include confirming whether the observed seismicity rate changes are systematic, and investigating the potential conditions for the seismicity rate changes. Through these systematic studies, we hope to better characterize the relationship among distant large mainshock, dynamically triggered microearthquakes and subsequent moderate (M>5) events.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Jackson, David
Schedule   Fri 4:45 PM / Oral
Room   Ballroom E
Testing fault-based earthquake forecasts
JACKSON, D. D., UCLA, Los Angeles, CA, david.d.jackson@ucla.edu
To date, organized earthquake forecast testing efforts like the Collaboratory for Study of Earthquake Predictability have focused on hypocenter forecasts. Many forecasts are based on fault or fault segment rupture, and the hypocenters of forecast earthquakes are essentially incidental. But testing fault-based forecasts requires a precise description of what is expected to happen. I present a scheme to mark proposed segment boundaries with polygons in latitude and longitude and to estimate a conditional probability that earthquake rupture would stop within the polygon if it enters. A control experiment can be established by drawing similar sized polygons where segment boundaries are not expected. Implementing this test will require definitions for on-fault earthquakes and for rupture termination. Unlike hypocenters, these quantities are not reported in authoritative bulletins. Surface-rupturing earthquakes occur rarely, so we would need to identify very many proposed segment boundaries in order to see results in our lifetimes.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Zoback, Mary Lou
Schedule   Wed 5:15 PM / Oral
Room   Ballroom C
Risk Implication of Alternative Representations of New Madrid Seismic Hazard
ZOBACK, M. L., RMS, Newark, CA, marylou.zoback@rms.com; WILLIAMS, C., RMS, Newark, CA, chesley.williams@rms.com; GROSSI, P., RMS, Newark, CA, patricia.grossi@rms.com; MUIR-WOOD, R., RMS, London, U.K., Robert.Muir-Wood@rms.com; BOLTON, M., RMS, Newark, CA, maiclaire.bolton@rms.com
Numerous scientific issues have been raised regarding the level and uncertainty of seismic hazard in New Madrid region of the central United States. We explore the impact of alternative hazard representations on the seismic risk of the region by evaluating alternate earthquake sources and variations in earthquake magnitudes and rates. The hazard is examined both probabilistically and through a series of scenarios to constrain uncertainty in expected losses. Using instrumental seismicity, Boyd (USGS SIR 2010-5173) estimated a 28-46% likelihood of a M6 or larger earthquake in the next 50 years and ~5% likelihood for a M7 or larger event in same time period. Our analyses demonstrate high expected losses for future relatively high-likelihood, moderate earthquakes throughout the region. For example, a M6.4-6.9 earthquake near Memphis could generate total economic losses to private property and businesses between $80-130B, while a M6.5 earthquake in the Wabash Valley could cause between $20-65B in losses, depending on the proximity of the event to major population centers. In contrast, we estimate in excess of $250B in private property and business coverage losses for a Mw7.7 earthquake on the New Madrid seismic zone (considered an upper bound magnitude by some). Our analyses also indicate that a significant fraction of earthquake losses in the greater New Madrid region (65-80%) will be covered by earthquake insurance. This exceeds the experience in Hurricane Katrina in 2005, in which only 55% of the $125B loss was covered by insurance payments. The 65-80% ratio of insured to total economic losses in the New Madrid region compares quite favorably to the current situation in California. Due to the low penetration of earthquake insurance, only 10-15% of total economic losses for major earthquakes in throughout California are expected to be covered by insurance (Grossi and Zoback, 2010, http://www.rms.com/Publications/1868_Hayward_Earthquake_Retrospective.pdf).
Session:Broadband Ground-Motion Time Series Generation
Presenter   Irikura, Kojiro
Schedule   Wed 9:45 AM / Oral
Room   Ballroom E
Improvement of the recipe for prediction of strong ground motions for inland mega-fault earthquakes
IRIKURA, K., Aichi Institute of Technology, Toyota-shi, Aichi, Japan, irikura@geor.or.jp; KURAHASHI, S., Aichi Institute of Technology, Toyota-shi, Aichi, Japan, susumu@aitech.ac.jp; PETUKHIN, A., Geo-research Institute, Osaka, Osaka, Japan, anatolyp@geor.or.jp
A recipe for predicting strong ground motions has been proposed based on source characterization for rupture processes from the waveform inversion analysis of strong motion data of inland crustal earthquakes (Irikura and Miyake, 2010). Broadband ground motions from an earthquake are simulated using the characterized source model consisting of asperities with high stress drops in a rupture area. The source fault models for future earthquakes are defined based on the “recipe”, combining information about active fault surveys, scaling relations of fault parameters, and characterized source model. The ground motions were simulated using a hybrid method with the crossover period of 1.0 s: the method sums the longer period motions calculated numerically assuming a velocity structured while the shorter period motions are evaluated using the stochastic Green’s function method. Verification and applicability of the “recipe” have been made using observed ground motions from recent disastrous inland-crustal-earthquakes less than Mw 7 such as the 1995 Kobe earthquake and the 2005 Fukuoka Seiho-oki earthquake. We attempt to validate the characterized source model for simulating strong ground motions from a inland mega-fault earthquake, the 2008 Wenchuan earthquake of Mw 7.9. The source model from this earthquake was already made by Kurahashi and Irikura (2010). The ground motions from their model were well simulated for the stations in forward rupture direction but underestimated for the stations in backward rupture direction. We find a new model to have better fit between the observed and synthetic motions for the stations in both rupture directions, forward and backward by handling out the rupture pattern in the source model. The improvement of the recipe for the inland mega fault earthquake is to figure out the rupture pattern additionally to the characterized source model.
Session:Archeoseismology: Learning about Ancient Earthquakes from the Archeological Record
Presenter   Kozaci, Ozgur
Schedule   Fri 8:45 AM / Oral
Room   Ballroom D
Archeoseismologically Determined Late-Holocene Fault Rupture Characteristics of the North Anatolian Fault, Hersek Peninsula, Izmit Bay, Turkey
KOZACI, O., Fugro William Lettis & Associates Inc., Walnut Creek, CA, o.kozaci@fugro.com; ALTUNEL, E., Osmangazi University, Eskisehir, Turkey, ealtunel@ogu.edu.tr; CLAHAN, K. B., Fugro William Lettis & Associates Inc., Wanchai, Hong Kong, k.clahan@fugro.com
Anatolia (Asia Minor) has been inhabited by numerous civilizations over the last several millennia. Roman, Byzantine, and Ottoman Empires have lived, flourished and kept detailed records such as wars, state affairs, disasters, constructions, and expenses. These significant civilizations all have built magnificent structures which are still relatively well-preserved throughout Turkey (Anatolia). These structures as well as written records provide us plenty of evidence for documenting and characterizing the disasters of both natural and anthropogenic origin. The study site on the Hersek Peninsula (Helenopolis) has been a strategic site for at least the last two millennia as a result of its strategic location between Izmit Bay and the Sea of Marmara. Historically it provided a nautical shortcut for the Bagdad Road, an important section of the spice route, between Istanbul (Constantinople) and Iznik (Nicaea). It also controls the entrance of Izmit Bay to Izmit (Nicomedia). The Hersek peninsula is also located near the western termination of 1999 Izmit earthquake surface rupture and it is the last place that the North Anatolian fault (NAF) can be studied on land before it enters the Marmara Sea. We performed extensive paleoseismic investigations to assess the seismic hazard risk for Marmara region; however, an offset 6th century Byzantine aqueduct along the North Anatolian fault provided key evidence for fault activity. Our investigations included detailed surveying of the aqueduct, which proves to be a competent strain gauge as it reveals an abrupt right bend coincident with the mapped trace of the right-lateral NAF. Detailed geomorphic descriptions of Helenopolis and construction records at this location were found within historical records of the Justinian era providing precise age control. The offset aqueduct provides valuable fault rupture information on the location, amount, and rate of offset of the NAF over the last 1500 years.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Ugurhan, Beliz
Schedule   Wed 11:15 AM / Oral
Room   Ballroom E
HYBRID GROUND MOTION SIMULATIONS ON NORTH ANATOLIAN FAULT ZONE (TURKEY)
UGURHAN, B., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, ugurhan@metu.edu.tr; ASKAN, A., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, aaskan@metu.edu.tr
Simulation of ground motions is an effective tool in seismically active regions where sparse or no ground motion records exist. Not only they provide a means to understand the source mechanism and the earth structure, but also they provide the engineers peak ground motion parameters and frequency content of potential ground motions. Deterministic simulation techniques are employed to generate the low frequency content of the ground motions. These techniques require well-resolved wave velocity models for realistic and reliable results. On the other hand, a variety of stochastic approaches are commonly utilized in the generation of high frequency ground motion simulations. In this study, we present hybrid ground motion simulations, combining stochastic and deterministic methods, in the highly populated and industrialized regions along the North Anatolian Fault Zone (NAFZ). Although the NAFZ is characterized by high seismicity rates, mostly coarse profiles of the wave velocity structure along this fault zone are present. As a result, in this study, deterministic simulations are performed using simple approaches with representative 1-D velocity profiles. The main emphasis is given to high frequency stochastic strong ground motion simulations. A sensitivity analysis is performed in order to visualize the effects of small perturbations in input parameters on the results of simulations. Finally, possible extensions of the synthetic ground motions to earthquake engineering problems are presented in the form of earthquake loss estimation and time history analyses of building structures.
Session:Guide to Sustainable Seismographic Networks
Presenter   Meltzer, Anne
Schedule   Fri 8:45 AM / Oral
Room   Ballroom C
Building Science Capacity: A Key Component of Sustainable Network Operations
MELTZER, A., Lehigh University, Bethlehem, PA, ameltzer@lehigh.edu
Modern seismology is driven by basic research into the structure and dynamics of the Earth, earthquake hazard and risk reduction, exploration for natural resources, and monitoring of nuclear explosions. Local and regional seismic networks play an important role in driving science advances and provide opportunities for training and education in critical sectors. In return, research using data recorded by local and regional networks is important for maintaining network quality and improving earthquake hazard mitigation programs. Advances in technical capabilities of local and regional networks must be coupled to effective capacity building, education and training, in order to be successful and sustainable. High quality seismic data recorded by regional networks play a critical role in providing observations at the time and spatial scales needed to address an array of basic research challenges such as: delineating high resolution patterns in seismicity, measuring variations in three dimensional seismic velocities, understanding stress triggering of earthquakes in complex fault zones, and in translating results from research into practice to benefit society. Strategic partnerships between universities, organizations, institutions, and agencies charged with earthquake monitoring and risk reduction can result in services that contribute to natural hazard risk reduction and sustainable operations. These services include national or regional hazard mapping, training to address the needs of monitoring agencies, as well as broader outreach and education programs in seismology and geophysics to support natural resource exploration and environmental applications. Success and sustainability depends on addressing local needs, developing long-term partnerships, and promoting strategies that simultaneously support fundamental research and contribute to reducing vulnerability to seismic hazards through adoption of appropriate best practices and development of public awareness.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Un, Elif
Schedule   Fri 4:45 PM / Oral
Room   Ballroom D
A Multi-disciplinary Seismic Loss Estimation Model: A Case Study in Northwestern Turkey
UN, E. M., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, unelif@metu.edu.tr; ERBERIK, M. A., Middle East Technical University, Dept. of Civil Engineering, Ankara. Turkey, altug@metu.edu.tr; ASKAN, A., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, aaskan@metu.edu.tr
Future seismic losses including the physical, economic and social ones as well as casualties concern a wide range of authorities varying from geophysical and earthquake engineers, physical and economic planners to insurance companies. Seismic loss studies are often either ceased at the physical loss level or are performed based on deterministic scenario events. However, as many components of loss estimation involve inherent uncertainties, a probabilistic approach to such a problem is required. This ongoing study aims to estimate seismic losses for a selected district in Bursa which is a highly industrialized city in Northwestern Turkey. To verify the methodology against a past large event, we initially perform loss estimations for a district in Düzce (another city in Northwestern Turkey), and calibrate the method with loss data from 12 November 1999 Düzce Earthquake.The main components of the loss model are seismic hazard, building vulnerability functions and loss as a function of damage states of buildings. To quantify the regional hazard, a probabilistic seismic hazard assessment approach is adopted. For different types of building structures, probability of exceeding predefined damage states for a given hazard level are determined using appropriate fragility curve sets. The casualty model for a given damage level considers the occupancy type, population of the building, occupancy at the time of earthquake occurrence, number of trapped occupants in the collapse, injury distribution at collapse and mortality post collapse. The proposed loss model combines the input components within a conditional probability approach. The results are expressed in terms of expected loss, most probable loss and maximum possible loss.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Askan, Aysegul
Schedule   Wed 10:45 AM / Oral
Room   Ballroom E
An Evaluation of Synthetic Ground Motion Time Histories in Terms of Dynamic Response of Engineering Structures
BAL, Z., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, balzynp@gmail.com; UGURHAN, B., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, ugurhan@metu.edu.tr; ASKAN, A., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, aaskan@metu.edu.tr; YAKUT, A., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, ayakut@metu.edu.tr
Structures are exposed to various types of loadings during their lifetimes. Seismic forces are among the most destructive ones with considerable uncertainties. Therefore, selection of suitable ground motions is a crucial step in seismic analysis and earthquake resistant design of structures. Strong ground motion records of past events in the region of interest or other regions with similar tectonic settings are utilized for this purpose. For regions where sparse or no ground motions exist, ground motion simulations provide alternative time series that can be used in dynamic analyses of structures. In this study, we present time history analyses of two-, five- and eight-storey reinforced concrete frame buildings under real and corresponding synthetic ground motions. Records of events with magnitudes ranging between Mw 5.0 and 7.6 from Northwestern Turkey are chosen as the real ground motions. The corresponding synthetic ground motions are generated using regional seismic parameters with stochastic finite-fault ground motion simulation method based on a dynamic corner frequency approach. Results from real and synthetic records are compared in terms of inter-storey drift ratios to investigate the ability of synthetic ground motions to predict the seismic responses of reinforced concrete frame structures.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Rhoades, David
Schedule   Fri AM / Poster
Room   Ballroom B
Experience in Applying Renewal Process Models to Fault Rupture Allowing for Data and Parameter Uncertainties
RHOADES, D. A., GNS Science, Lower Hutt, New Zealand, d.rhoades@gns.cri.nz; VAN DISSEN, R. J., GNS Science, Lower Hutt, New Zealand, r.vandissen@gns.cri.nz
A method for estimating the time-varying probability of rupture of a fault, allowing for uncertainties in geological data and parameters of recurrence-time distributions, has recently been applied to several faults in the southern North Island, New Zealand, including the Wellington, Wairarapa and Ohariu faults. On each of these faults, data is available on the timing of the most recent rupture and several previous ruptures, the size of single-event lateral displacements and the Holocene dextral slip rate. These faults encompass elapsed times, single-event displacements, and slip-rates that range from circa 150 to 2000 years, 4 to 14 m, and 1 to 11 mm/yr, respectively.The method adopts a Bayesian framework, and begins with a prior distribution for the value of the adjustable parameters in each recurrence-time distribution, whether exponential, lognormal, Weibull or Brownian passage-time. Values are sampled from the uncertainty distribution of the data and used to obtain multiple realisations of the posterior distribution of the parameters. The hazard functions of these realisations are averaged to estimate the time-varying probability of rupture. The sensitivity of the result to assumptions, possible new data and to the form of the recurrence-time distribution can be readily assessed. A logic tree can be used to combine the results using different recurrence-time distributions. Sometimes, the probability is strongly dependent on the form of the distribution, for example, when the fault last ruptured only recently as in the case of the Wairarapa Fault. However, in other cases there is surprisingly little dependence on the recurrence-time distribution.
Session:Creative Wavefield Recording and Analysis
Presenter   Brokesova, Johana
Schedule   Fri PM / Poster
Room   Ballroom B
Self-Calibrated Mechanical Seismic Sensor for Field Rotation Rate Measurements (Rotaphone)
BROKESOVA, J., Charles University, Prague, Czech Republic, Johana.Brokesova@mff.cuni.cz; MALEK, J., Institute of Rock Structure and Mechanics AS CR, Prague, Czech Republic,
Rotaphone is a newly developed mechanical sensor system for recording seismic rotation rate components. It is based on measurements of differential motions between paired sensors (low-frequency geophones) attached to a rigid (undeformable) skeleton. The same differential velocity (and, consequently, the same rotation rate component) is obtained from more than one geophone pairs, which allows for in-situ calibration of individual sensors. The calibration method is explained and demonstrated using two illustrative examples: a synthetic test and a laboratory test with a rotational shaking table. We present two different prototypes of the device based on the same principle. The first one consisting of eight horizontal geophones in a horizontal plane is designed to measure vertical rotational component (torsion) . It is characterized by a flat frequency characteristic in the wide range from 1 Hz to 100 Hz. The second one is designed to measure all three rotation rate components. It contains eight horizontal geophones in two parallel horizontal planes and one vertical geophone. I has a flat frequency characteristic between 4.5 Hz and 100 Hz. The sensitivity limit of both prototypes is of the order of 10E-8 rad/s. Their advantages are small dimensions, portability, easy installation and operation in the field.We present several examples of the rotation rate ground motion recorded by Rotaphone deployed in Western Bohemia earthquake swarm area. Sources of the recorded rotation rates are both natural (local shallow microearthquakes) and anthropogenic (rockburst and blasts).
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Turner, James
Schedule   Wed PM / Poster
Room   Ballroom B
Lithology and Shear Wave Velocity Relationships from New IMASW Measurements in Albuquerque, New Mexico: Updated NEHRP Site-Response Classification Maps and Preliminary Seismic Amplification Calculations
TURNER, J. P., Fugro William Lettis & Associates Inc., Lakewood, CO, j.turner@fugro.com; CLAHAN, K. B., Fugro William Lettis & Associates Inc., Wanchai, Hong Kong, k.clahan@fugro.com; LUTZ, A. T., Fugro William Lettis & Associates Inc., Walnut Creek, CA, a.lutz@fugro.com; O'CONNELL, D. R. H., Fugro William Lettis & Associates Inc., Lakewood, CO,
New site-specific shallow shear wave velocity (Vs) profiles were measured across a representative range of surficial deposits to characterize seismogenic ground shaking hazards in the seismically active Rio Grande rift valley in Albuquerque, New Mexico. Albuquerque is a rapidly developing area located adjacent to the Sandia range-front fault system which is capable of producing earthquakes as strong as Mw7.0. Interferometric Multichannel Analysis of Surface Waves (IMASW) shear wave geophysical survey methods were used to calculate 62 high-resolution Vs profiles. These profiles were used to develop empirical relationships between Vs and lithology, and to produce predictive hazard maps of ground shaking including site-conditions-related seismic amplification for the Middle Rio Grande Valley.Spatial results show that Vs structure in the Albuquerque area is generally homogenous, typically characterized by 5 to 10 meters of slow (≤200 m/s) and unconsolidated Holocene alluvium over faster (>400 m/s) and more consolidated Pleistocene alluvium. Vs based soil classification criteria are correlated to geologic units to develop revised NEHRP site classification maps. Slower shallow unconsolidated alluvium overlying faster consolidated units can produce strong amplification of ground motions. Seismic amplification calculations from this study predict that the strongest amplifications will occur in Holocene fluvial deposits near downtown Albuquerque and in a north-south corridor along the active Rio Grande. Strong amplifications are expected to occur in the 2 to 3 Hz bandwidth window, resonance frequencies that correspond closely to natural response frequencies of two to four story buildings. This study demonstrates that cost efficient site-specific velocity structure surveys can significantly improve the delineation of shallow strong ground motion amplification zones where building performance and emergency response are expected to be most severe during an earthquake.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Crowley, Helen
Schedule   Fri 4:15 PM / Oral
Room   Ballroom D
Community-Based Open Standards and Data for the Global Earthquake Risk Model
CROWLEY, H., GEM Foundation, Pavia, Italy, helen.crowley@globalquakemodel.org; PINHO, R., GEM Foundation, Pavia, Italy, rui.pinho@globalquakemodel.org
The Global Earthquake Model (GEM) initiative aims to develop a global model of earthquake risk as an open source, community-driven project. In order to begin this in a structured way, a number of Global Components that cover the scientific modules of the model have been defined, and Requests for Proposals have been released, requesting international consortia to bid to lead these projects. Within the risk domain, 5 Global Components have been identified, with the following objectives: - GEM Ontology and Taxonomy: to define the framework for calculating seismic risk and classify the components therein.- Global Earthquake Consequences Database: to collect post-earthquake data such as loss of life, injuries, damage and economic loss into a common web-based repository.- Global Exposure Database: to construct a global building and population inventory.- Global Vulnerability Estimation Methods: to define levels of damage and loss as a function of ground motion intensity, for a global taxonomy of buildings.- Inventory Data Capture Tools: to support the population of the exposure and consequences databases through innovative open-source tools.The consortia leading these global components will be required to define standards and best practice related to the methodologies used in seismic risk assessment and in particular the collection and storage of data needed therein. The consortia will work closely with independent regional programmes to ensure that the local characteristics from different regions of the world are accounted for. This presentation introduces the GEM risk activities and describes the open source software and development platform (OpenGEM) that is being developed to provide access to and community interaction with the proposed data and tools. Specific focus will be given to issues related to the data collection for seismic vulnerability assessment.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Meza-Fajardo, Kristel
Schedule   Wed PM / Poster
Room   Ballroom B
Accuracy Considerations in the M-PML Implementation Using the SEM for the Elastic Wave Equation
MEZA-FAJARDO, K. C., Universidad Nacional Autónoma de Honduras (UNAH), Tegucigalpa, Honduras, kristelmeza@unah.edu.hn; PAPAGEORGIOU, A. S., University of Patras, Patras, Greece, papaga@upatras.gr
The Multi-Axial Perfectly Matched Layer (M-PML) is a stable and effective non-reflecting boundary condition for many problems in computational seismology. In order to define the M-PML medium, damping profiles must be specified along more than one direction. As in the case of the classical PML, when the system of M-PML equations is discretized, the absorbing layer is no longer perfectly matched, and a small spurious numerical reflection manifests at the interface between the physical domain and the M-PML. Such numerical reflection depends on the actual M-PML width, on the damping profiles, on the wavelength, and it does not decrease indefinitely when damping is increased.We present an analysis of the numerical reflection introduced by the discrete M-PML, when the latter is introduced to truncate a computational domain over which the seismic wave equation is solved using the Spectra Element Method (SEM). We consider numerical examples of wave propagation in two-dimensional homogeneous media for which analytical solutions are well known. In order to illustrate the accuracy of the M-PML implementation, reflection coefficients are computed and comparisons of analytical and numerical solutions are presented.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Gulen, Levent
Schedule   Thu 4:00 PM / Oral
Room   Ballroom E
Active Fault Database for the Middle East Region:Earthquake Model of the Middle East (EMME) Project
GÜLEN, L., Sakarya University, Serdivan, Sakarya, Turkey, lgulen@sakarya.edu.tr; WP2 Team
The Earthquake Model of the Middle East (EMME) Project is a regional project of the umbrella GEM (Global Earthquake Model) project (http://www.emme-gem.org/). EMME project region includes Turkey, Georgia, Armenia, Azerbaijan, Syria, Lebanon, Jordan, Iran, Pakistan, and Afghanistan. Both EMME and SHARE projects overlap and Turkey becomes a bridge connecting the two projects. The EMME project will use PSHA approach and the existing source models will be revised or modified by the incorporation of newly acquired data. The most distinguishing aspect of the EMME project from the previous ones will be its dynamic character. This very important characteristic is accomplished by the design of a flexible and scalable database that will permit continuous update, refinement, and analysis. A digital active fault map of the Middle East region is prepared in ArcGIS format. We have constructed a database of fault parameters for active faults that are capable of generating earthquakes above a threshold magnitude of Mw≥5.5. The EMME project database includes information on the geometry and rates of movement of faults in a “Fault Section Database”. The “Fault Section” concept has a physical significance, in that if one or more fault parameters change, a new fault section is defined along a fault zone. So far 6,991 Fault Sections have been defined and 83,402 km of faults are fully parameterized in the Middle East region. A separate “Paleo-Sites Database” includes information on the timing and amounts of fault displacement for major fault zones. A digital reference library, that includes the pdf files of the relevant papers, reports and maps, is also prepared. New data and evidences will be interpreted to revise or modify the existing source models. A logic tree approach will be utilized for the areas where there is no consensus to encompass different interpretations. Finally seismic source zones in the Middle East region will be delineated using all available data.
Session:Combining Geodetic and Seismic Measurements
Presenter   GUEGUEN, Philippe
Schedule   Fri 9:30 AM / Oral
Room   Ballroom E
Instrumentation of a Shallow Borehole for Prediction of Seismic Liquefaction Coupling Pore Pressure and Accelerometric Sensors
GUEGUEN, P., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, pgueg@obs.ujf-grenoble.fr; FORAY, P., L3SR, Grenoble Institute of Technology, Grenoble, France, Pierre.Foray@hmg.inpg.fr; LANGLAIS, M., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, mickael.langlais@obs.ujf-grenoble.fr; ROUSSEAU, C., ENSE3, Grenoble Institute of Technology, Grenoble, France, Christophe.Rousseau@ense3.grenoble-inp.fr
The Belleplaine 3D borehole array, located in the Guadeloupe island (French Lesser Antilles), was designed for liquefaction study. The site included extensive in-situ geotechnical and geophysical surveys (drilling boreholes and laboratory testing on sample, SASW, H/V seismic noise ratio survey, seismic piezocone), and a vertical array composed of three synchronized triaxial accelerometers (Episensor) placed at GL-0m, GL-15m and GL-39m, where GL means “ground level”, and five pore pressure sensors installed at different depths in the potentially liquefying zone. The geotechnical characteristics of the Belleplaine site is made of a mangrove layer overlaid by a sandy stiff deposit. This configuration is widely found at the border-coast of the Caribbean regions, exposed to high seismic hazard. This paper presents first the results of the seismopiezocone tests performed on the site, including dissipation tests and downhole measurements of shear wave velocities. An analysis of the risk of liquefaction using the combined data of tip resistance, friction ratio, excess pore pressure and Vs is discussed. Second, the seismic response of the soil column is computed using three methods: the spectral ratio method from the vertical array data, numerical method using the geotechnical properties of the soil column and operative modal analysis method (Frequency Domain Decomposition). We show that the buried mangrove layer plays the role of an isolation system equivalent to those usually employed in earthquake engineering for reducing the seismic shear forces by reducing the internal stress within the structure. In our case, the flexibility of the mangrove layer reduces the distortion and the stress in the sandy upper layer, and then the potential of liquefaction of the site.
Session:Earth Structure Observations and Theory
Presenter   Sisman, Fatma Nurten
Schedule   Thu PM / Poster
Room   Ballroom B
A Site Characterization Study in Western Turkey: Comparison of Alternative Techniques
SISMAN, F. N., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, f.nurtensisman@gmail.com; ASKAN, A., Middle East Technical University, Dept. of Civil Engineering, Ankara, Turkey, aaskan@metu.edu.tr; ASTEN, M., Monash University, Melbourne, Victoria, Australia, michael.asten@sci.monash.edu.au
Izmir is a highly populated and industrialized city center located in a seismically active region of Western Turkey. The city is underlain by soft sediments and it has experienced three destructive earthquakes within the last century. It is thus important to assess the site effects in this region in addition to its seismicity. In this study, we initially employ the Modified Microtremor Spatial Autocorrelation (MMSPAC) technique to estimate the one-dimensional S-wave velocity profile at the Bornova (BRN) and Guzelyali (GZLY) strong ground motion stations located in the Izmir area. In MMSPAC method, we directly match the observed and modeled SPAC spectra with iterative forward modelling rather than inverting the observed dispersion curves for the phase velocities. We validate our blind interpretations of S-wave velocity profile with the geologic settings of the sites. We then apply horizontal to vertical spectral ratio (HVSR) method on both microtremor and strong motion data recorded at the selected sites. Finally, we utilize one-dimensional site response analysis for the assessment of site amplifications and the resonance periods. We present our results in the form of one-dimensional velocity structure and comparison of frequency-dependent site amplifications from alternative techniques at the selected sites.
Session:Geotechnical Lessons Learned from Recent Earthquakes: Haiti, Chile, Baja CA, New Zealand
Presenter   Gueguen, Philippe
Schedule   Fri PM / Poster
Room   Ballroom B
French Afterschocks Network Installed One Week After the Mw 8.8 Chile Earthquake: Preliminary Analysis of the Accelerometric Data.
GUEGUEN, P., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, pgueg@obs.ujf-grenoble.fr; RENAULT, M., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, martine.renault@obs.ujf-grenoble.fr; BOUROVA, E., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, katia.bourova@obs.ujf-grenoble.fr; PEQUEGNAT, C., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, pequegna@obs.ujf-grenoble.fr; COUGOULAT, G., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, glenn.cougoulat@obs.ujf-grenoble.fr; MARISCAL, A., Institute of Earth Science, CNRS/UJF/LCPC/IRD, Grenoble, France, armand.marsical@obs.ujf-grenoble.fr; ROUSSEL, S., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, ; PAUL, A., Institute of Earth Science, CNRS/UJF/LCPC, Grenoble, France, sandrine.roussel@obs.ujf-grenoble.fr
The February 27th 2010, a Mw 8.8 giant earthquake struck the central part of Chile. This earthquake was felt along the pacific coast, from the South of Concepcion to the North of Valparaiso (i.e. more than 1000km). It produced a great amount of damage to modern and old constructions, power and life-line facilities. The INSU-sponsored French team, led by Jean-Pierre Vilotte (IPG-Paris), in close collaboration with the Department of Geophysics (Chile University) and Chilean Seismological Service, deployed few days after the main shock a temporary seismological network. This network is part of the French mobile seismological pool (SISMOB) sponsored by INSU-CNRS and IRD, and CalTech mobile network, in the framewok of a joint agreement for Chile experience. SISMOB is a research facility for seismic and volcanic hazard, deep earth studies and post-seismic activities. Managed by Institute of Earth Science (ISTerre) at Grenoble (France), it is composed by high dynamic range of acquisition systems that can be connected to broad-band accelerometers and seismometers instruments. After the main shock, 41 stations were deployed: 26 CMG40 HH, 14 CMG5 HN and 1 Episensor HN sensors, all connected to 24 bytes Taurus acquisition systems. The stations were installed on rocky sites and their location was defined following the information provided by USGS on rupture extension and aftershocks localization. All the stations are in continuous recording mode, at 100 Hz. The stations were spread along the Chilean coast, and a special attention was paid to the boundaries of the rupture between the 1960 (Valdivia, Mw 9.5) et 2010 earthquakes toward the South, and the 1985 (Valparaiso, Mw 7.8) and 2010 earthquakes toward the North. More than 400 events with magnitude over 3 were recorded after the deployment. This paper is a preliminary report of the accelerometric data collected, with a special focus on ground motion analysis.
Session:Guide to Sustainable Seismographic Networks
Presenter   Storchak, Dmitry
Schedule   Fri PM / Poster
Room   Ballroom B
The Guide to Sustainable Networks: Configuring Networks and Processing Procedures to Optimise Seismic Event Parameterization
STORCHAK, D. A., International Seismological Centre (ISC), Thatcham, Berkshire, United Kingdom, dmitry@isc.ac.uk; BONDÁR, I., International Seismological Centre (ISC), Thatcham, Berkshire, United Kingdom, istvan@isc.ac.uk
Building a sustainable seismographic network requires well-informed cooperation between commercial companies and the government or other agencies that will be responsible for funding and operating them. A guide that would inform about the advantages and challenges of building, operating and managing appropriate seismic networks is being planned by the International Development Seismology (IDS) Committee. The International Seismological Centre (ISC) is willing to take part in this project by bringing its expertise in managing, using and archiving the parametric data obtained from approximately 120 networks worldwide.We plan to discuss the importance of a network’s appropriate geometrical configuration, the value of three-component stations, the advantages of measuring the arrival times of useful seismic phases and taking appropriate amplitude measurements.We also aim to discuss the importance of the data exchange on a regional scale and also internationally by bringing examples of successful data use when several network’s data are processed together. We will explain why registration of stations in the International Seismographic Station Registry is vital. We will show that in addition to serving local purposes, data of local seismic stations can contribute towards more global long-term goals of improving our knowledge of the Earth’s inner structure, monitoring compliance with Comprehensive Test Ban Treaty as well as providing further information for regional and global seismic hazard assessment studies.
Session:Guide to Sustainable Seismographic Networks
Presenter   Storchak, Dmitry
Schedule   Fri PM / Poster
Room   Ballroom B
Developments at the International Seismological Centre (ISC)
STORCHAK, D. A., International Seismological Centre (ISC), Thatcham, United Kingdom, dmitry@isc.ac.uk; HARRIS, J., International Seismological Centre (ISC), Thatcham, United Kingdom, james@isc.ac.uk; BONDÁR, I., International Seismological Centre (ISC), Thatcham, United Kingdom, istvan@isc.ac.uk
The International Seismological Centre (ISC) is a non-governmental non-profit organization supported by 55 research and operational institutions around the world and charged with production of the ISC Bulletin – the definitive summary of the global seismicity based on reports from 120 institutions worldwide. Jointly with World Data Center for Seismology (Denver), the ISC runs the International Seismic Station Registry (IR). The ISC provides a number of additional services including the depositary of the IASPEI Reference Event list (GT), EHB and ISS data collections.The ISC has a substantial development programme that ensures that the ISC data remain an important requirement for geophysical research. This programme includes improving collection of preliminary reports from networks soon after event occurrence to make the automatic Preliminary ISC Bulletin as comprehensive as possible before the Reviewed ISC Bulletin becomes available in 18-24 months. We modernized the ISC event location and magnitude computation procedures and attempt taking useful measurements from waveforms available on-line further improving the accuracy of the Bulletin. We are working on the project of re-building the entire ISC Bulletin (1960-2010) by re-computing the hypocenters and magnitudes with the new location algorithm using ak135 velocity model, identifying and filling the gaps in data, correcting known errors and introducing essential additional bulletin data from temporary deployments. The ISC takes a leading role in compiling the GEM Instrumental Seismic Catalogue (1900-2009) where more reliable and consistent magnitudes and hypocentre parameters will be provided for large earthquakes using existing and newly obtained data. The ISC is also running the CTBTO-Link where the ISC Bulletin data are provided to the monitoring community as a historical perspective into current recordings by the IMS network as well as making a link to current data of non-IMS networks.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Kuyuk, H. Serdar
Schedule   Wed 11:30 AM / Oral
Room   Room 204/205
An Alternative Method Analyzing Site Effects based on Recorded Data for Response Spectral Acceleration Attenuation Relationship
KUYUK, H. S., Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, serdarkuyuk@gmail.com; SI, H., Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, shj@eri.u-tokyo.ac.jp; KOKETSU, K., Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, koketsu@eri.u-tokyo.ac.jp; MIYAKE, H., Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, hiroe@eri.u-tokyo.ac.jp
Calculation of more reliable probabilistic seismic hazard maps needs more stable and accurate prediction of strong-motion indexes such as response spectral acceleration using attenuation relationships. The main three factors; source, path, and site effect should be evaluated properly. In common, site effects are considered as a function of Vs30 in various studies. In this study, a new and simple method to evaluate the site effects, proposed by Si et al. (2010), is used and applied to Tottori Region, Japan. A frequency dependent correction factor (CF) which is the mean of the summation of the ratio of observed ground motion over a reference attenuation model (Kanno et al, 2006) is employed for response spectral acceleration. The method is tested for 152 stations around Tottori area within 100 km hypocentral distance. Totally, 46 crustal events through 6952 earthquake records with larger than Mw 4.0 are used. The correlation between CF and average Vs30 is analyzed for periods between 0.05 to 5 seconds. It is found out that there is a good agreement between our results and previously proposed methods in literature. Thus, the algorithm used in this study is an alternative method for evaluating site effect to obtain more reliable attenuation relationship models.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Field, Edward
Schedule   Fri 4:00 PM / Oral
Room   Ballroom E
Computing Elastic-Rebound-Motivated Earthquake Probabilities on an Un-segmented Fault
FIELD, E. H., USGS, Golden, CO, field@usgs.gov
Because elastic rebound is widely recognized as a key driver of the earthquake cycle, time-dependent probabilities conditioned on the date of last event are often considered in state-of-the-are earthquake forecasts. A conclusion of the 2007 Working Group on California Earthquake Probabilities was that we currently lack a self-consistent methodology for computing such probabilities unless we assume strict segmentation (and have no multi-segment ruptures). The problem is that we’ve been attempting to apply point-process models to what is certainly not a point process, at least not as hitherto posed. Because observations of large repeating events are severely lacking, this study turned to synthetic catalogs generated by physics-based earthquake simulators for clues on how to solve the problem. This exploration has led to an alternative methodology that is not only consistent with results from earthquake-simulators, but is also self-consistent as demonstrated via Monte Carlo simulations. The solution amounts to an average time-predictable model where segmentation assumptions are relaxed by allowing the date of last event to vary along the rupture. An interesting implication is that recurrence intervals at a point on a fault, such as inferred from a paleoseismic trench, should not be expected to agree with any of the commonly assumed renewal models (unless strict segmentation is honored). Fortunately this study implies appreciable elastic-rebound predictability even though recurrence intervals at a point can be quite erratic. Finally, the methodology shows promise for being concisely posed via Bayes’ Theorem.
Session:Seismic Sources and Parameters
Presenter   Bent, Allison
Schedule   Wed 2:15 PM / Oral
Room   Ballroom E
Regional Magnitude Corrections for Eastern Canada: Appalachian vs Shield Paths
BENT, A. L., Geological Survey of Canada, Ottawa, ON, Canada, bent@seismo.nrcan.gc.ca
Seismic hazard calculations rely heavily on magnitude recurrence rates. Thus accurate and consistent magnitudes are of vital importance. As part of a larger project to improve and standardize magnitudes for Canada, station corrections for Canadian seismograph stations were established. It was observed that the average residuals for Atlantic Canada tended to be negative (i.e. stations were underestimating the magnitude) suggesting that there might be systematic differences between Shield and Appalachian paths. Earthquakes in the Charlevoix and Lower St. Lawrence Seismic Zones provide a good, natural data set for testing this hypothesis as the seismic zones lie on the boundary between the Shield and Appalachians. Appalachian and Shield magnitudes were calculated for earthquakes in these zones and compared to the official event magnitudes using events of magnitude 2.5 or greater with a minimum of five magnitude readings. The Shield magnitudes were generally the same as the event magnitudes whereas the Appalachian magnitudes were on average 0.3-0.4 magnitude units smaller. These results suggest that either a regional path correction should be applied or that a different velocity model should be used for Appalachian paths. The overall effect of not applying a correction will be minimal for events in central Canada where the event magnitudes are dominated by readings from Shield or mixed paths. However, the effect may be greater for events occurring within the Appalachians particularly if they are too small to have many distant magnitude readings. The effects of the path differences on other parameters, such as those derived from regional moment tensor inversions, are being explored.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Kolinsky, Petr
Schedule   Wed AM / Poster
Room   Ballroom B
Array analysis, mode identification and reflections of surface waves in Europe
KOLINSKY, P., Institute of Rock Structure and Mechanics AS CR, Prague, Czech Republic, kolinsky@irsm.cas.cz; GAZDOVA, R., Institute of Rock Structure and Mechanics AS CR, Prague, Czech Republic, gazdova@irsm.cas.cz; MALEK, J., Institute of Rock Structure and Mechanics AS CR, Prague, Czech Republic, malek@irsm.cas.cz
We estimate velocities and backazimuths of surface waves propagating directly or reflected from the main tectonic structures in Europe in a wide period range 5-70 s. Both Love and Rayleigh waves from nearly 200 broadband stations are considered. The study is based on earthquakes with magnitude Mw ≥ 5 which occurred in the Aegean Sea, Greece, in 2007-2008. The time period is chosen to coincide with the duration of the international passive seismic project PASSEQ which covered the territory of Germany, the Czech Republic, Poland and Lithuania. For interpretation also the data from the ORFEUS database are used. Special attention is paid to the Central European region. In the first stage of the project, we estimate arrival times of different surface wavegroups at each station separately. We use the multiple filtering technique. Five local envelope maxima of all quasiharmonic components are found and their propagation times determined. By sorting the propagation times according to their mutual temporal and spatial correlation, we discover not only clear fundamental and higher modes, but also modes reflected from Tornquist-Teisseyre zone. The second stage considers an array approach. Records from many stations are processed together. For example, twenty STS-2 stations deployed in Switzerland are used as an array with an aperture of several hundreds of kilometers. Harmonic components of the records from all stations are mutually correlated and the time differences are used to compute the local phase velocity as well as the true backazimuths of propagation for each period of the surface waves. Than, the same approach is used also for different parts of Europe considering spatially neighboring stations as arrays and determining phase velocities and backazimuths of several surface wave modes. Smooth and mostly monotonic dependence of propagation backazimuths on period is found. Implications for reflections from tectonic discontinuities are given.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Yilmaz, Nazan
Schedule   Thu AM / Poster
Room   Ballroom B
Assessment of Seismic Hazard for the Bursa Province, Turkey
YILMAZ, N., Disaster and Emergency Management Presidency, Ankara, Turkey, nazany@deprem.gov.tr; YUCEMEN, M. S., Middle East Technical University, Ankara, Turkey, yucemen@metu.edu.tr
In recent years, availability of more detailed information on faults and fault segments enabled the implementation of more complex physical and stochastic models in seismic hazard assessment studies. Therefore, probabilistic seismic hazard assessment procedures taking into consideration the hazard nucleating from active faults and utilizing more appropriate stochastic models have become the most up-to-date trend in the development of new generation of seismic hazard maps. Unfortunately, comprehensive investigations on active faults and their parameters, which serve as the input to these procedures, require a lot of time and are quite expensive especially for large regions, like a country. In such a case, current seismic hazard estimates can be updated on region or province basis. Consistent with this view, in this study, seismic hazard of Bursa province in Turkey is assessed by combining the contributions of two components, namely: faults and background seismic activity. Two different stochastic models (Poisson and renewal) are utilized to estimate the probabilities of future earthquake occurrences on the faults. On the other hand, contribution of background seismic activity to seismic hazard is computed using two different seismic source models (background area source model with uniform seismicity and spatially smoothed seismicity model) under the alternative assumptions made on catalog completeness and elimination of secondary events (i.e. fore- and after shocks). Seismic hazard results obtained based on alternative models and assumptions are aggregated through the use of logic tree method and the resulting weighted average seismic hazard values are presented in the form of maps.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Calais, Eric
Schedule   Wed 11:30 AM / Oral
Room   Ballroom C
Present-day strain accumulation in the New Madrid seismic zone from GPS geodesy
CALAIS, E., Purdue University, West Lafayette, IN, ecalais@purdue.edu
Large earthquakes within stable plate interiors are taken as evidencethat significant levels of strain accumulate along intraplate faults.However, unambiguous measurements of strain accumulation on seismicallyactive geologic structures far from plate boundaries, such as the New Madrid seismic zone, remain elusive. It is usually assumed thatthese faults behave like those at plate boundaries, accumulatingstrain at a measurable rate consistent with the seismic record, sothat large earthquakes occur at similar locations and quasi-regularintervals. However, there is increasing evidence from thepaleo-earthquake record that intraplate faults experience longperiods of seismic quiescence separated by short periods of clusteredactivity, and that the loci of large earthquakes migrate over timeamong fault systems within the continent. In addition, the mostrecent geodetic results from the New Madrid seismic zone show thatstrain is accumulating much too slowly to account for the seismicactivity over the past 5,000 years. Taken together, the latestgeodetic and paleoseismological data in the midcontinent indicate that the steady-state model of strain accumulation and release doesnot apply to the NMSZ.
Session:The Seismo-Acoustic Wavefield
Presenter   Burlacu, Valeriu
Schedule   Fri AM / Poster
Room   Ballroom B
Seismo-Acoustic Wavefield Characterization of the January 3, 2011 ML 4.6 Circleville Earthquake in Utah
BURLACU, R., University of Utah Seismograph Stations, Salt Lake City, UT, burlacu@seis.utah.edu; ARROWSMITH, S. J., Los Alamos National Laboratory, Los Alamos, NM, arrows@lanl.gov; PANKOW, K. L., University of Utah Seismograph Stations, Salt Lake City, UT, pankow@seis.utah.edu; KOPER, K. D., University of Utah Seismograph Stations, Salt Lake City, UT, koper@seis.utah.edu; HALE, J. M., University of Utah Seismograph Stations, Salt Lake City, UT, jmhale@seis.utah.edu; STUMP, B. W., Southern Methodist University, Dallas, TX, bstump@smu.edu; HAYWARD, C., Southern Methodist University, Dallas, TX, hayward@smu.edu
On January 3, 2011 at 5:06 am MST, an earthquake with ML 4.6 occurred in the vicinity of Circleville, UT. There have been more than 130 felt reports from the cities around the epicenter. So far, 75 aftershocks, with magnitudes between -0.7 and 3.5, have been recorded and located at the Utah’s regional seismic network. The mainshock was recorded at nine infrasonic arrays deployed in Utah. Using the InfraMonitor software package, we detected and located the event. This location, based on a Bayesian approach using only infrasonic data, without incorporating any corrections from a prediction model, is at ~14 km south of the solution estimated from the seismic network data.The infrasonic data, recorded at distances between ~135 to ~380 km, are well suitable for an in-depth analysis of the acoustic wavefield propagation inside and outside the “zone-of-silence”. We present ray tracing modeling results based on G2S and atmospheric profiles recorded at the Salt Lake City airport at the time of the event. Finally, we report on our ongoing investigations modeling the coupling of radiated seismic energy into the atmosphere to understand the generation mechanism of infrasound from earthquakes as a function of depth, magnitude, focal mechanism and ground motion parameters.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Cotton, Fabrice
Schedule   Thu 2:45 PM / Oral
Room   Room 204/205
Evidence of Stress Drop Magnitude Scaling and Stochastic Ground-Motion Model from Accelerometric Data Recorded in the French West Indies
DROUET, S., ISTerre, Université Joseph Fourier, Grenoble, France, st_drouet@yahoo.fr; BOUIN, M. P., IPGP, Observatoire Volcanologique et Sismologique de Guadeloupe, Paris, France, bouin@ipgp.fr; COTTON, F., ISTerre, Université Joseph Fourier, Grenoble, France, fabrice.cotton@ujf-grenoble.fr
We analyse data from the « Les Saintes » seismic sequence, following a Mw=6.3 event which occurred in Guadeloupe on November 21, 2004. The data set contains 485 events with magnitudes from 2 to 6.3, and recorded at distances from 5 to 150 km on the two French Antilles islands: Guadeloupe and Martinique.S-waves Fourier spectra are computed and source, path and site parameters are determined using a global inversion scheme. A moment magnitude scale is established calibrated on the Mw from USGS for the 6 largest events in the dataset. Our results show a stress drop magnitude scaling which flattens toward high magnitudes. Our analysis also shows that the local duration magnitude scale underestimate moment magnitude by 0.5 units. Obtained source, path and site parameters are used to compute ground-motions through stochastic simulations. We show that ground-motions are well reproduced using this simple simulation tool. The results indicate that stress drop variations and directivity effects control the inter-event variability.
Session:Archeoseismology: Learning about Ancient Earthquakes from the Archeological Record
Presenter   Hinzen, Klaus-G.
Schedule   Fri 9:45 AM / Oral
Room   Ballroom D
Seismic Surveillance of Cologne Cathedral
HINZEN, K. G., Cologne University, Bergisch Gladbach, Germany, hinzen@uni-koeln.de; FLEISCHER, C., Cologne University, Bergisch Gladbach, Germany, claus.fleischer@uni-koeln.de; SCHOCK-WERNER, B., Cathedral Workshop Cologne, Cologne, Germany, barbara.schock.werner@dombauverwaltung-koeln.de; SCHWEPPE, G., Cologne University, Bergisch Gladbach, Germany, gregor.schweppe@uni-koeln.de
In 2006, a strong motion network in the Lower Rhine Embayment (LRE), NW Germany was established. The 19 free field stations were supplemented by five strong motion stations within Cologne Cathedral, one of the largest Gothic cathedrals in the world and a World Heritage Monument since 1996. One station is located in the archaeological excavation in the cathedral basement, 7 m below the main floor, on natural ground. A second station has been installed on top of the vault of the nave above the choir, and three more are located at the 70, 100 and 130 m levels, respectively, of the northern tower. At 157.38 m, the northern cathedral tower is the second tallest in Europe. While the main goal is the recording of local earthquake motions within the building, other phenomena are detectable with the continuous, synchronized records of the five accelerometer stations.Time-frequency analysis of the ambient vibrations of the building shows correlation with local weather situations. While wind speed determines the amplitude of the vibrations, precipitation influences the eigenfrequencies of the tower. The largest free-swinging bell, the Petersglocke rings only on special occasions (e.g. Christmas, New Year, death of the Pope). The 24 t bell is located at the 55 m level in the southern tower. The motions induced by the swinging bell are recordable throughout the cathedral, including the basement and the northern tower. The period of the swinging bell is 3.6 s. In the northern tower, the spectral amplitudes of the second harmonic dominate the spectrum. The 1.2 s eigenperiod of the bell is in between the first two EW-eigenperiods of 1.31 s and 1.04 s of the tower. On January 6th, the suspension of the 800 kg clapper of the Petersglocke broke. We show the recordings and interpretation of the impact of the broken clapper.
Session:The Seismo-Acoustic Wavefield
Presenter   Le Pichon, Alexis
Schedule   Fri 3:45 PM / Oral
Room   Ballroom C
Observations of earthquake-generated infrasound
LE PICHON, A., CEA/DAM/DIF, Arpajon, France, Alexis.LE-PICHON@CEA.FR; GUILBERT, J., CEA/DAM/DIF, Arpajon, France, jocelyn.guilbert@cea.fr
Earthquakes are a well-known source of atmospheric pressure waves. Acoustic-gravity waves from the sudden strong vertical ground displacements have been observed on microbarometers at distances of thousands kilometres from the epicenter. Distinct source mechanisms of pressure wave generation have been identified: (i) pressure changes due to the vertical displacement of the seismic waves near the infrasound station, (ii) the local conversion from seismic waves to the sound pressure near the epicentre area, and (iii) radiated pressure waves by the topography when seismic surface waves travel through mountainous regions.Large earthquakes recorded by multiple stations at different ranges and azimuths from the epicentre provide a unique opportunity to improve our understanding of the generation of acoustic waves produced by seismic wave-induced ground motion. Using an inverse location procedure and a complete 3-D simulation of the radiated pressure field, distant source regions of pressure waves are reconstructed. Analyses derived from different data sets confirm that the amplitude corrected for the propagation and duration of infrasound signals are well correlated to the ground motion strength. We suggest that the seismic source mechanism and the geographic situation of mountain ranges relative to the areas of strong ground motion may also play a predominant role in the generation of infrasound. More detailed analyses on a wide range of seismic magnitude will require second order corrections for the effects of the seismic source parametrization (such as depth, source mechanism) and topographic features (extension, geographic situation). With improved knowledge of the source mechanisms of earthquake-generated infrasound, it may be possible to use infrasonic recordings to estimate regions of strong ground shaking. This may be useful in regions lacking other surface motion measurements.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Laurendeau, Aurore
Schedule   Thu AM / Poster
Room   Ballroom B
Seismic Indicators Prediction Equations for The Japon
LAURENDEAU, A., ISTERRE, CNRS, Université de Grenoble, Grenoble, France, aurore.laurendeau@ujf-grenoble.fr; COTTON, F., ISTERRE, CNRS, Université de Grenoble, Grenoble, France, fabrice.cotton@ujf-grenoble.fr; BONILLA, L. F., IFSTTAR, Paris, France, Fabian.BONILLA@irsn.fr
Few ground motion prediction equations (GMPE) have been developed for seismic indicators as the Arias Intensity, the duration and the central frequency. In this study, the KiK-net and K-net accelerometric records on site with VS30 ≥ 500m/s were collected up to the end of 2009. Among these data, we have selected shallow crustal events (focal depth ≤ 25 km and excluding offshore events), events characterized by moment magnitude (MW(FNET) ≥ 3.5) and focal mechanisms. From a visual inspection, faulty recordings like S-wave triggers, or recordings from multi-events have been eliminated or shortened. A Magnitude-distance filter was applied according to Kanno et al. (2006) which allows to eliminate the data observed at very long distances for large magnitude events having comparable PGA levels for stations located close to low magnitude seismic sources. Finally, 4429 records are included in this subset. Firstly, we have developed simple functional forms integrating only three usual independent variables: MW, the hypocentral distance and VS30. Secondly, we have integrated others variables like focal mechanisms, various rupture distance metrics and the resonance frequency. The nonstationary stochastic method developed by Sabetta and Pugliese (1996) and improved by Pousse et al. (2006) is a semi-empirical method using seismic indicators to generate synthetic time histories. This method has been improved by using the new functional forms. We finally have compared the calculated time histories with real data.
Session:The Seismo-Acoustic Wavefield
Presenter   Whitaker, Rodney
Schedule   Fri 1:30 PM / Oral
Room   Ballroom C
Some Reflections on the Seismo-acoustic Wavefield
WHITAKER, R. W., Los Alamos National Laboratory, Los Alamos, NM, rww@lanl.gov
Twenty-eight years ago, when I first started working in infrasound at Los Alamos, there were a few organizations still engaged in infrasound research, which had quite successfully been applied to the monitoring of atmospheric nuclear tests. At Los Alamos the small infrasound team worked with the seismic group on field deployments and data collections on underground nuclear tests. However, there was not a great deal of analysis and interaction in what has become known as seismo-acoustics – a research discipline that considers joint seismic and acoustic (including infrasound) data collection, analysis and interpretation, to the benefit of both. As the infrasound arrays of the International Monitoring System became established, there was increasing interest infrasound and, naturally, how infrasound and seismic data and analysis could be combined. In this talk we will highlight some of the developments in seismo-acoustics, discuss particular events, and speculate on what may lie ahead. The field has benefited from the contributions of many talented researchers, not all of whom can be cited in a short talk, but all of whom have contributed to the advancement of the discipline.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Woolery, Edward
Schedule   Wed PM / Poster
Room   Ballroom B
Fault Hazard Assessment in Urban Areas – Gansu Province, Northwestern China
WOOLERY, E., University of Kentucky, Lexington, KY, woolery@uky.edu; YUXIA, L., Lanzhou Institute of Seismology, Lanzhou, Gansu P.R. China, yuxial@gssb.gov.cn; WANG, L., Lanzhou Institute of Seismology, Lanzhou, Gansu P.R. China, wanglm@gssb.gov.cn; WANG, Z., Kentucky Geological Survey, Lexington, KY, zmwang@uky.edu; YUCHENG, S., Lanzhou Institute of Seismology, Lanzhou, Gansu P.R. China,
The Gansu Province in northwestern China wraps around the northeastern edge of the Qinghai-Tibet Plateau, and is within the active tectonic accommodation zone associated with the eastward extrusion of Tibet from the Indian-Eurasian collision. The two largest urban areas in Gansu, Lanzhou and Tianshui, are located in alluvial valleys. The location and deformation history of faults projected beneath these cities are poorly constrained due to the alluvial cover and the more than two millennia of intense cultural activity that has obscured any neotectonic surface manifestations. Near-surface seismic (shear-wave) reflection profiles across mapped fault projections resolved vertical displacements likely associated with extension and compression jogs in the primarily strike-slip fault motions. The imaged displacement extended above bedrock into late Quaternary sediment. Subsequent, drilling and sampling at two sites confirmed the geophysical interpretations and dated the latest rupture Middle Pleistocene.
Session:Seismic Sources and Parameters
Presenter   Lee, En-Jui
Schedule   Wed 2:30 PM / Oral
Room   Ballroom E
Rapid Centroid Moment Tensor (CMT) Inversion in 3D Earth Structure Model for Earthquakes in Southern California
LEE, E., University of Wyoming, Laramie, WY, elee8@uwyo.edu; CHEN, P., University of Wyoming, Laramie, WY, pochengeophysics@gmail.com; JORDAN, T. H., University of Southern California, Los Angles, CA, tjordan@usc.edu; MAECHLING, P. J., University of Southern California, Los Angles, CA, maechlin@usc.edu
Accurate and rapid CMT inversion is important for seismic hazard analysis. We have developed an algorithm for very rapid CMT inversions in a 3D Earth structure model and applied it on earthquakes recorded by the Southern California Seismic Network (SCSN). The procedure relies on the use of receiver-side Green tensors (RGTs), which comprise the spatial-temporal displacements produced by the three orthogonal unit impulsive point forces acting at the receiver. We have constructed a RGT database for 219 broadband stations in Southern California using an updated version of the three-dimensional SCEC Community Velocity Model (CVM) version 4.0 and a staggered-grid finite-difference code. Finite-difference synthetic seismograms for any earthquake in our modeling volume can be simply calculated by extracting a small, source-centered volume from the RGT database and applying the reciprocity principle. We have developed an automated algorithm that combines a grid-search for suitable focal mechanisms and depth locations with a gradient-descent method that further refines the grid-search results. Using this algorithm, we can invert CMT solutions in a 3D Earth structure near real-time and have determined CMT solutions over 1,000 earthquakes in Southern California. Comparison with the CMT solutions provided by the Southern California Seismic Network (SCSN) shows that our solutions generally provide better fit to the observed waveforms. Our algorithm may provide more robust CMT solutions for earthquakes in Southern California.
Session:Seismotectonics and Hazards of Active Margins in the Circum-Caribbean Sea and Eastern Pacific Ocean
Presenter   ten Brink, Uri
Schedule   Wed 10:30 AM / Oral
Room   Ballroom D
Seismic Hazard in the Northeast Caribbean
TEN BRINK, U. S., U.S. Geological Survey, Woods Hole, MA, utenbrink@usgs.gov; BAKUN, W. H., U.S. Geological Survey, Menlo Park, CA, billb23@sbcglobal.net; FLORES, C. H., U.S. Geological Survey, Woods Hole, MA, cflores@usgs.gov; LOPEZ-VENEGAS, A. M., University of Puerto Rico, Mayaguez, PR, alberto.lopez3@upr.edu; VILLASEÑOR, A., Institute of Earth Sciences, Barcelona, Spain, antonio@ictja.csic.es
Significant variations in seismic coupling along the NE Caribbean subduction zone are deduced from analysis of historical earthquakes, GPS, tomography, and seafloor mapping. Moving from west to east, a subduction zone is absent under Haiti. A strongly coupled interface exists along a 415-km-long segment from central Hispaniola to the western tip of Puerto Rico, where a series of 20th century earthquakes probably released 400+ years of perpendicular slip accumulation. Large historical earthquakes are absent north of Puerto Rico and the Virgin Islands (PR-VI), where a slab tear possibly exists, and NE of the Lesser Antilles. GPS measurements do not show strain accumulation, thus, the subduction interface from Puerto Rico to Guadeloupe may be largely decoupled. However, earthquakes, such as in 1787, may occur where the Main and Barracuda ridges enter the subduction zone. Large fault offsets in the trench outer-rise north of the Virgin Islands could be sources of earthquakes and tsunamis.Intra-arc earthquakes appear to be the primary hazards to the region. In Hispaniola, we estimate ~300 year recurrence interval and magnitudes ≤7.7 for earthquakes on the Septentrional and Enriquillo fault systems. The 2010 Haiti earthquake may be the start of a new earthquake cycle on the Enriquillo fault system, while the Septentrional fault may be in the middle of its inter-seismic period. Intra-arc seismic activity in Puerto Rico appears minor and the deep quasi-annual seismic swarms north of PR-VI may represent tear-related deformation. However, earthquakes here may be felt more strongly, because intensity fall-off with distance appears to be lower than in Hispaniola and the Lesser Antilles. The 420-km long section between the Virgin Islands and Guadeloupe experienced 4 large (M7.1-7.8) intra-arc earthquakes in the past ~380 years. Although large earthquakes are not documented in the Muertos backarc thrust belt, similar regions around the world had destructive earthquakes and tsunamis.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Emry, Erica
Schedule   Thu 9:00 AM / Oral
Room   Ballroom D
Outer rise earthquakes in the Mariana Subduction Zone: Implications for hydration of the incoming plate and state of stress along the seismogenic zone
EMRY, E. L., Washington University in St. Louis, St. Louis, MO, ericae@seismo.wustl.edu; WIENS, D. A., Washington University in St. Louis, St. Louis, MO, doug@seismo.wustl.edu
We study the occurrence of extensional faulting in the outer rise of the Mariana subduction margin in an attempt to gain insight into slab hydration and stresses between the Philippine and Pacific plates in the seismogenic zone. We determine accurate depths by inverting teleseismic P and SH waveforms from CMT earthquakes occurring from 1982 to present. For earthquakes with Mw ~5.5+, we determine the depth of earthquake and we refine the CMT focal mechanism. For some smaller events, due to lack in clear waveform data, we invert only for depth of earthquake. Results from the central portion of the Mariana outer rise indicate that extensional earthquakes occur in the Pacific plate down to 15-20 km beneath the top of the crust. If the presence of extensional faulting assists in the hydration of the subducting lithosphere, then we expect that the top 15-20 km of the slab may house hydrous minerals. Of additional interest in this region, current records indicate that only extensional faulting events occur in the central portion of the Mariana outer rise, while the southern portion has extensional, compressional and strike-slip earthquakes. The change between faulting styles in the south and central regions may have implications for changes in stress along the length of the seismogenic zone. Additional work using finite-difference modeling of plate flexure will be presented. By combining our observed depths of extensional and compressional earthquakes along with models of plate flexure in an elastic-plastic ocean lithosphere, we hope to gain better understanding of the rheology of plate materials and stresses acting upon the Pacific plate prior to subduction.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Brudzinski, Michael
Schedule   Thu PM / Poster
Room   Ballroom B
Detecting and Locating Tremor and Slip in Cascadia, Mexico, and Alaska
BRUDZINSKI, M. R., Miami University, Oxford, OH, brudzimr@muohio.edu; BOYARKO, D. C., Miami University, Oxford, OH, boyarkdc@muohio.edu; HOLTKAMP, S. G., Miami University, Oxford, OH, holtkasg@muohio.edu; SCHLANSER, K. M., Miami University, Oxford, OH, schlankm@muohio.edu; SIT, S. M., Miami University, Oxford, OH, sitsm@muohio.edu; CABRAL-CANO, E., Instituto de Geofisica, UNAM, Mexico City, DF, Mexico, ecabralcano@gmail.com; ALLEN, R. M., University of California - Berkeley, Berkeley, CA, rallen@berkeley.edu; CHRISTENSEN, D. H., University of Alaska - Fairbanks, Fairbanks, AK, doug@giseis.alaska.edu
Tectonic plate boundaries can generate large devastating earthquakes when there is a sudden release of elastic strain energy stored on the locked, seismogenic zone of the plate interface. Recent geodetic observations reveal that at depth, where increasing temperatures and pressure as well as changing petrology and fluid content affect the frictional behavior, plate boundary faults can also release accumulated strain through slow slip. In many cases, the slow slip events have been shown to correlate with seismically recorded non-volcanic tremor, forming so-called episodic tremor and slip (ETS). Our recent work has focused on detecting and locating sources of tremor and slip in Cascadia, Mexico, and Alaska. We will present a summary of recent evidence collected that support the following conclusions: tremor detection can be automated due to its narrow frequency content, tremor productivity is variable in different subduction zones, tremor is spatially anticorrelated with background seismicity, tremor patterns show no relationship to time since previous great earthquake, tremor is offset downdip from slow slip and afterslip, and some tremor occurs without a clear correlation to slow slip.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Hayes, Gavin
Schedule   Thu 8:45 AM / Oral
Room   Ballroom D
Exploring Controls on Seismogenesis by Comparing Models of Three-Dimensional Subduction Zone Geometry with Source Inversions of Large Earthquakes
HAYES, G. P., USGS NEIC, Golden, CO, ghayes@usgs.gov; WALD, D. J., USGS NEIC, Golden, CO, wald@usgs.gov
Bathymetric and subduction interface structure have frequently been proposed to control rupture limits of large subduction zone earthquakes. However, in many instances the relationships between structure and the rupture zones of large earthquakes have not been robustly investigated or quantitatively defined. Here we utilize Slab1.0, a new compilation of the three-dimensional geometries of global subduction zones, in conjunction with models of large earthquake ruptures from the USGS extending back to the year 2000, to test the hypothesis that ruptures of large earthquakes often coincide with structural barriers. We explore whether such controls exist on a global basis, or whether they are confined to local and/or regional subduction zone sections. We also investigate the effects of uncertainties in modeled slip distribution on these correlations. Finally, we show that by quantifying the relationships (or lack thereof) between subduction zone structure and the limits of co-seismic rupture during large earthquakes, we can move towards a more complete understanding of subduction zone seismogenesis.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Baldwin, John
Schedule   Thu 11:00 AM / Oral
Room   Ballroom C
The Penitentiary Fault and Its Association with the Commerce Geophysical Lineament: Possible Late Quaternary Deformation?
BALDWIN, J. N., Fugro William Lettis & Associates, Walnut Creek, CA, j.baldwin@fugro.com; GIVLER, R. W., Fugro William Lettis & Associates, Walnut Creek, CA, r.givler@fugro.com; BROSSY, C. C., Fugro William Lettis & Associates, Walnut Creek, CA, c.brossy@fugro.com; HARRIS, J., Millsaps College, Jackson, MS, harrijb@millsaps.edu
The Commerce geophysical lineament (CGL) is a 600-km-long, 5- to 10-km-wide, NE-trending magnetic and gravity anomaly extending from Arkansas to Indiana. In southern Illinois, the Penitentiary fault (PF) lies within the 120-km-long Commerce section of the CGL, and is coincident with a strikingly linear NE-trending, east-facing bluff in Tamms, Illinois that separates Cache River Valley deposits on the east from Paleozoic upland rocks on the west. Geophysical surveys across the CGL and PF image disrupted Quaternary sediments similar to multiple studies conducted in SE Missouri along the CGL. Shear-wave seismic reflection profiles delineate an unconformable contact between Paleozoic bedrock and Quaternary alluvium, warped and faulted Quaternary deposits, and a buried east-facing bedrock scarp. The PF is imaged as a 0.5-to 0.8-km-wide zone of high-angle faults some of which offset late Pleistocene Pearl and Henry Fms. Transects of closely-spaced boreholes across suspected Quaternary faults can be interpreted to support vertically separated Henry Fm (>~20 to 25 ka), Equality Fm (12 to 17 ka), and perhaps early Holocene Cahokia Fm. Geophysical and geologic profiles support transpressive faulting with cumulative vertical separations ranging from 25 to 5 m using bedrock and late Quaternary contacts. Available geologic mapping, trench, geophysical, and paleoliquefaction data suggest that between Illinois and Missouri the Commerce section of the CGL was active during the late Pleistocene with little to no activity during the middle to late Holocene Epoch. Although poorly constrained, evidence for late Pleistocene deformation along the surface projection of the CGL from multiple sites in the central U.S. suggests faults comprising the CGL may represent potential seismogenic structures capable of generating moderate to large magnitude earthquakes. Faults associated with the Commerce section lie west and subparallel to the active New Madrid seismic zone.
Session:Broadband Ground-Motion Time Series Generation
Presenter   imperatori, walter
Schedule   Wed PM / Poster
Room   Ballroom B
Near-Field Ground-Motion Simulation Including 3D Scattering
IMPERATORI, W., ETH Zurich, Zurich, Switzerland, imperatori@tomo.ig.erdw.ethz.ch; MAI, P. M., Kaust, Thuwal, Saudi Arabia, martin.mai@kaust.edu.sa
Wave scattering occurring in the Earth crust is an important physical process that strongly affects the observed seismic wavefield. Different empirical methods have been recently proposed to include such phenomenon in broadband ground motion calculations, considering scattering as a purely random stochastic process. In this work we take an alternative approach by solving the elastic wave equation considering realistic 3D random media into which we insert different earthquake source representations.Our goal is to study scattering characteristics and its influence on the seismic wavefield at short and intermediate distances from the source, addressing in particular earthquake-engineering related parameters (PGA, PGV and SA). We investigate important scattering related phenomena, such as the loss of radiation pattern and the breakdown of directivity. We deploy several 3D media, generated using Von Karman correlation functions with correlation lengths of 5 - 10 km and standard deviation values of 5-10 %, based on recent findings on heterogeneities distribution in the upper crust. We then compute ground motions (0-10 Hz) for a double-couple point source characterized by an omega-squared spectrum model. Further complexities in the faulting process are added gradually, culminating in complex kinematic rupture models.Results indicate that scattering acts globally as a pure energy-redistribution phenomenon. This implies that no high-frequency energy is generated during the scattering process at the expense of the low-frequency energy. This has dramatic consequences in the study of rupture dynamics, since it would indicate the faulting process as the only source of high-frequency energy radiation.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Zhang, Haijiang
Schedule   Thu 11:15 AM / Oral
Room   Ballroom D
Nonvolcanic Tremors in Localized Low Shear Wave Velocity Zones Beneath the San Andreas Fault
ZHANG, H., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, hjzhang@mit.edu; NADEAU, R. M., Berkeley Seismological Laboratory, UC-Berkeley, Berkeley, CA, nadeau@seismo.berkeley.edu; TOKSOZ, M. N., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, toksoz@mit.edu; THURBER, C. H., Department of Geoscience, University of Wisconsin-Madison, Madison, WI, clifft@geology.wisc.edu; FEHLER, M., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, fehler@mit.edu
Nonvolcanic tremors are detected deep beneath the San Andreas fault (SAF) near Cholame, California, the inferred nucleation zone of the great M7.8 Fort Tejon earthquake of 1857. The tremors are modulated by small stress changes induced by tides and regional and teleseismic earthquakes, implying elevated pore fluid pressure in the tremor zone. In this area, tremors lie beneath the seismogenic zone, limiting the usefulness of local earthquakes for resolving fluid-related seismic properties in the tremor zone. We developed a new seismic imaging method, station-pair double-difference (DD) seismic tomography, to directly use differential tremor arrival times to image the tremor zone. An event collapsing method, which shifts event hypocenters toward the center of mass of the events within some volume surrounding the event location, is also incorporated in the DD tomography to better delineate the seismic event location patterns. We applied the new imaging method to 1246 well located tremors beneath SAF that occurred between July 27, 2001 and February 21, 2009. Station-pair differential times were obtained by cross-correlating 6-minute RMS envelopes for all possible station pair combinations having station separation distances of 100 km or less. For the first time, we obtained new detailed information about the association between deep tremors and localized low shear wave velocity anomalies. These anomalies are likely caused by high-pressure pore fluids beneath the nucleation zone of historic large earthquakes.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Frankel, Arthur
Schedule   Thu 4:45 PM / Oral
Room   Ballroom C
Significant Motions Between GPS Sites in the New Madrid Region: Implications for Seismic Hazard
FRANKEL, A., U.S. Geological Survey, Seattle, WA, afrankel@usgs.gov
Time series of positions of GPS instruments in the New Madrid region deployed by the University of Memphis were analyzed to measure motions between sites with relatively low levels of noise. The position time series were differenced to determine the relative motions between the stations, after correction for motion of the stable North American plate. Significant motions of 0.4 - 0.5 mm/yr were found between three sites and a reference site. These rates exceeded two standard errors in the rate determinations derived from a noise model consisting of a combination of white, flicker, and random walk noise. The parameters for these components of noise were determined from each differenced time series using the maximum likelihood estimation procedure of Langbein (2004, 2008). While relatively small, the observed surface motions are consistent with a creep rate of 2 mm/yr or more on the Reelfoot fault at depths between 15 and 30 km. For creep on a finite patch at depth, the motions at the surface are much smaller than the creep rate. If it is constant with time, an interseismic slip rate of 2 mm/yr or more at depth produces sufficient slip for an earthquake with a minimum moment magnitude of 7.0 on the shallow portion of the Reelfoot fault, given the 500 year average recurrence time for 1811-12 type earthquakes observed from paleoliquefaction data.
Session:Geometry effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Presenter   Kawase, Hiroshi
Schedule   Wed AM / Poster
Room   Ballroom B
A New Interpretation of Earthquake H/V Ratios based on Diffuse Field Theory for Plane Waves
KAWASE, H., DPRI, KYoto Univ., Uji, Kyoto, Japan, kawase@zeisei.dpri.kyoto-u.ac.jp; MATSUSHIMA, S., DPRI, KYoto Univ., Uji, Kyoto, Japan, matsushima@zeisei.dpri.kyoto-u.ac.jp; SÁNCHEZ-SESMA, F. J., UNAM, Mexico City, D.F., Mexico, sesma@servidor.unam.mx
We propose here a new interpretation on horizontal-to-vertical (H/V) spectral ratios based on the diffuse field concepts in order to analyze strong motion records at a site in which site effects can be described using a one dimensional model. The imaginary part of Green function at the free surface is proportional to the square of the absolute value of the corresponding transfer function for a plane, vertically incident wave (Claerbout, 1968). The incident plane waves represent the most important part of earthquake ground motions and their associated motions, being multiple scattered, are formed of waves that sample significant portions of the considered area. For a set of incoming plane waves (of P, SV, and SH types) with varying azimuths and incidence angles we assume that the ground motion will be spatially homogeneous in a statistical sense. In other words, the average of normalized ground motion spectral densities will depend only on depth. Therefore, we can apply a 1D description of wave propagation for a diffuse field of ground motions. To prove the above hypothesis for H/V ratios of earthquake ground motions, we first show a comparison of averaged synthetics of 1D underground structures with a corresponding simple theoretical prediction from 1-D transfer functions. After summing up a few hundreds of synthetics with different angles of incidences, azimuths, and polarizations, we can obtain identical H/V ratios that the simple theory of diffuse field predicts. Then we show H/V ratios for actual seismic motions observed by K-NET and KiK-net in Japan operated by NIED. We show that the earthquake H/V ratios are quite stable no matter what part of the waveform is used to analyze, except for the P-wave part where horizontal component would be deficient probably because its duration is not long enough. We also show that their basic spectral characteristics can be well reproduced by the extracted velocity structures from the simple theory of diffuse field.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Boyd, O. Sierra
Schedule   Wed AM / Poster
Room   Ballroom B
Deviatoric Moment Tensor Analysis at The Geysers Geothermal Field
BOYD, O. S., UC Berkeley Seismological Laboratory, Berkeley, CA, sierra@seismo.berkeley.edu; DREGER, D. S., UC Berkeley Seismological Laboratory, Berkeley, CA, dreger@seismo.berkeley.edu; HELLWEG, M., UC Berkeley Seismological Laboratory, Berkeley, CA, peggy@seismo.berkeley.edu; TAGGERT, J., UC Berkeley Seismological Laboratory, Berkeley, CA, jennifer@seismo.berkeley.edu; LOMBARD, P., UC Berkeley Seismological Laboratory, Berkeley, CA, lombard@seismo.berkeley.edu; FORD, S. R., Lawrence Livermore National Laboratory, Livermore, CA, sean@llnl.gov; NAYAK, A., Indian Institute of Technology, Kharagpur, India, avinash07guddu@gmail.com
Geothermal energy has been produced at The Geysers Geothermal Field in Northern California for more than forty years. It has been demonstrated that increased steam production and fluid injection correlates positively with changes in earthquake activity, resulting in thousands of tiny earthquakes each year with events ranging in magnitude up to 4.5. We determine source parameters for the largest of these earthquakes using a regional distance moment tensor method. We invert three-component, complete waveform data from broadband stations of the Berkeley Digital Seismic Network, the Northern California Seismic Network and the USArray deployment (2005-2007) for the complete, six-element moment tensor. Some solutions depart substantially from a pure double-couple with some events having large volumetric components. Care is needed in the assessment of the significance of the non-double-couple terms. We have worked to develop a systematic procedure for the evaluation of aleatoric and epistemic solution uncertainty (e.g. Ford et al., 2009; Ford et al., 2010). We will present the solutions for The Geysers events together with estimates of random errors and systematic errors due to imperfect station coverage and knowledge of the velocity structure, which are needed to compute Green’s functions for the inversion. Preliminary results indicate that some events have large isotropic components that appear to be stable and suggestive of fluid or gas involvement during the rupture processes.We are presently working to incorporate full moment tensor capability in the Berkeley Seismological Laboratory's automatic processing system and analyst interface. This upgrade will enable improved monitoring at The Geysers and volcanically active regions of California.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Baig, Adam
Schedule   Wed 2:45 PM / Oral
Room   Ballroom D
On the Similarity Between Non-Double-Couple Events in Hydraulic Fracture, Volcanic and Geothermal Environments
BAIG, A. M., Engineering Seismology Group, Kingston, ON, Canada, adam.baig@esg.ca; URBANCIC, T. I., Engineering Seismology Group, Kingston, ON, Canada, ted.urbancic@esg.ca
During the 1980s, much attention was focussed on resolving whether certain earthquakes in hydrothermal and volcanic environments have significant non-double-couple focal mechanisms. In particular, the question of whether the observed radiation patterns comprised two double-couple events or a single event was raised as an objection. However, as the number of studies in these environments reporting similar non-double-couple modes increased, opinions settled on the explanation that non-double-couple mechanisms are represented by these radiation patterns and point to the opening of fractures as the mechanism for the generation of this seismicity.Recent studies with hydraulic fracture stimulations have begun to determine moment tensors in situations where the monitoring configuration is favorable to the complete resolution of the moment tensor. The deployments we discuss utilize multiple monitoring geophone arrays downhole in quiet non-producing wells, and the stability of the focal mechanism determination is assessed through consideration of the condition numbers for the general inversion of the moment tensor. These studies show that the majority of these mechanisms are also non double-couple in nature. Plotting the resolved mechanisms on source-type plots shows that, in most cases, these data represent mechanisms that oscillate between the opening and closure fractures. The similarity between these mechanisms and those discussed above in geothermal and volcanic environments supports the hypothesis that seismicity induced by fluid flow has a signature distinct from the double-couple events seen dominantly at tectonic scales.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Zandieh, Arash
Schedule   Wed 9:30 AM / Oral
Room   Room 204/205
New Hybrid Empirical Ground-Motion Prediction Equations for Eastern North America
ZANDIEH, A., The University of Memphis, Memphis, TN, azandih1@memphis.edu; PEZESHK, S., The University of Memphis, Memphis, TN, spezeshk@memphis.edu
The hybrid empirical method is one of the techniques used in regions with insufficient strong ground-motion data to develop ground-motion prediction equations. In the hybrid empirical method, the target region (ENA in this study) ground motions are predicted from the host (WNA in this study) empirical ground-motion relations using modification factors between two regions. These theoretical modification factors are calculated as the ratio of stochastic simulations of ground motions for two regions. Using regional seismological parameters in simulations, the adjustment factors reflect the regional differences in source, path, and site in both regions. In the hybrid empirical method, the empirically derived ground-motion models for the host region are mapped onto the target region considering the seismological regional disparities.In this study, a hybrid empirical method is used to develop a new ground-motion prediction equation for eastern North America (ENA), using five new ground-motion prediction models developed by the Pacific Earthquake Engineering Research Center (PEER) for western North America (WNA) as the host region, and most recent seismological parameters for the stochastic simulations. A new ENA ground-motion prediction equation is derived for a magnitude range of 5 to 8 and closest distances to the fault rupture up to 1000 km. Ground-motion prediction equations are developed for the response spectra (pseudo-acceleration, 5% damped) and the PGA for hard-rock sites in ENA. The resulting ground-motion prediction model developed in this study is compared with ENA ground-motion models used in the 2008 national seismic hazard maps as well as with available observed data for ENA.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Chen, Po
Schedule   Wed 4:45 PM / Oral
Room   Ballroom D
Full-3D Waveform Tomography for Southern California
CHEN, P., University of Wyoming, Laramie, WY, pochengeophysics@gmail.com; LEE, E., University of Wyoming, Laramie, WY, elee8@uwyo.edu; JORDAN, T. H., University of Southern California, Los Angles, CA, tjordan@usc.edu; MAECHLING, P. J., University of Southern California, Los Angles, CA, maechlin@usc.edu; DENOLLE, M., Stanford University, Menlo Park, CA, mdenolle@stanford.edu; BEROZA, G. C., Stanford University, Menlo Park, CA, beroza@stanford.edu
We are automating our full-3D waveform tomography (F3DT) based on the scatteringintegral (SI) method and applying the automated algorithm to iteratively improve the 3D SCEC Community Velocity Model Version 4.0 (CVM4) in Southern California. In F3DT, the starting model as well as the derived model perturbation is 3D in space and the sensitivity kernels are calculated using the full physics of 3D wave propagation. The SI implementation of F3DT is based on explicitly constructing and storing the sensitivity (Fréchet) kernels for individual misfit measurements. The sensitivity (Fréchet) kernels are constructed through the temporal convolution between the earthquake wavefield (EWF) from the source and the receiver Green tensor (RGT) from the receiver. Compared with other F3DT implementations, the primary advantages of the SI method are its high computational efficiency and the ease to incorporate 3D Earth structural models into very rapid seismic source parameter inversions. For the first iteration, we used over 3,500 phase-delay measurements from regional earthquakes to invert for 3D perturbations to the 3D reference model, SCEC CVM4. The updated model, CVM4SI1, reduced the variance of the phase-delay measurements by about 29% and the synthetics generated by the updated model generally provide better fit to the observed waveforms. In the second iteration, we only used phase-delay measurements made on ambient noise Green’s function data and the updated model, CVM4SI2, reduced the variance of phase-delay measurements by about 51%. The synthetic waveforms generated by CVM4SI2 not only improved ambient noise Green’s function waveform fittings but also earthquake waveform similarities. In the third iteration, we combine frequency-dependent measurements made on waveforms from both earthquakes and ambient noise Green’s functions for a perturbation relative to CVM4SI2. The resulting model, CVM4SI3, provides better fit to both types waveforms.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   DeShon, Heather
Schedule   Thu PM / Poster
Room   Ballroom B
Comparisons Between High-resolution Earthquake Relocations, Thermal Modeling, and Structure along the Sunda Subduction Zone
DESHON, H. R., Univ. of Memphis, CERI, Memphis, TN, hdeshon@memphis.edu; PESICEK, J. D., Univ. of Wisconsin-Madison, Madison, WI, pesicek@geology.wisc.edu; THURBER, C. H., Univ. of Wisconsin-Madison, Madison, WI, clifft@geology.wisc.edu; ZHANG, H., Massachusetts Institute of Technology, Cambridge, MA,
Teleseismically recorded aftershocks of the 2004, 2005, and 2007 great Sumatra earthquakes illuminate the seismogenic zone and provide over a half million additional seismic phases for inclusion in tomography and earthquake relocation studies. A new regional P-wave tomography model for Sunda serves as the base model for double-difference (DD) teleseismic relocation, extended to use P, depth phases (pP and pwP), and waveform cross-correlation derived P and pP differential times [Pesicek et al, 2010]. Here we present DD relocations for earthquakes extending through December 2010, including the 2010 Southern Sumatra tsunami earthquake. Combining the DD results with a quality graded Global CMT catalog, thermal modeling, and recently published reflection images of the forearc provides a more complete picture of seismicity along this subduction zone. Holes in underthrusting and strike-slip upper plate seismicity reveal regions of remaining slip deficit along the megathrust and Sumatra Fault, respectively. Strike-slip mechanisms of intra-oceanic plate events outboard of the deformation front are consistent with events occurring within the slab down to 100 km depth, suggesting that the pre-existing oceanic faults are being reactivated. Finally, comparison of underthrusting seismicity to existing thermal models better defines the updip and downdip limits of megathrust activity. A significant number of underthrusting earthquakes occur downdip of the overriding plate Moho along most of the subduction zone. If thermal models are accurate, the 350-450º C isotherm serves as a better proxy of the downdip limit here. Updip, while the 150º C isotherm occurs inland from the trench in most models, the occurrence of the 2010 tsunami earthquake, the posited 1907 tsunami earthquake, and the large number of near trench thrust events in the 2004 area suggests that rupture can extend very close to the trench. The potential for slip to the trench exists along most of this margin.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Hintersberger, Esther
Schedule   Thu 9:30 AM / Oral
Room   Ballroom C
The extended (paleo)seismological story of the Vienna Basin and the largest earthquake north of the Alps
HINTERSBERGER, E. M., University of Vienna, Vienna, Austria, esther.hintersberger@univie.ac.at; DECKER, K., University of Vienna, Vienna, Austria, kurt.decker@univie.ac.at; LOMAX, J., BOKU Vienna, Vienna, Austria, johanna.lomax@boku.ac.at
The Vienna Basin in Central Europe between the Alps and the Carpathians is a typical example for the bimodality between short-term and long-term deformation of intraplate regions: While moderate seismicity is focused along the NNE-SSW trending Vienna Basin Transfer Fault at its eastern boundary, normal faults crossing the basin seem to be seismically inactive. However, those splay faults indeed show low Quaternary movement (<0.1 mm/a). One of the key questions for the Vienna Basin is whether those faults must be included into seismic hazard assessment or if they are negligible. Here, we present a dataset of three paleoseismological trenches at one of those splay faults, the Markgrafneusiedl Fault. In all three trenches, Pleistocene Danube terrace gravels (~ 250 ka) are offset by ~ 40 m. The age of the oldest layers within the well-stratified hanging wall comprising flood-plain sediments and colluvial wedge deposits vary between the trenches, but the youngest deposits are dated consistently to ages around 13 ka. In total, we found evidence for five major surface-breaking earthquakes during the last 104 ka. Especially, offset of the upper layers by about 15-20 cm in all three trenches can be associated with one single event at ~ 14 ka. The second youngest event in relative order is characterized by a colluvial wedge of 0.7-0.9 cm height with similar appearance in both southern trenches. Probabilistic evaluation of inferred single-event displacements lead to magnitude estimates ranging between Mw=6.3 and Mw=7.0. The latter is the largest magnitude that has been documented in a paleoseismological investigation within Central Europe north of the Alps. These results, together with the fact that five additional splay faults occur close to the Austrian capital, Vienna, indicate that the discussed very slow faults cannot be excluded from seismic hazard assessment, even for the relatively short recurrence periods used for national building codes or the EUROCODE 8 (475 yrs).
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Ferris, Aaron
Schedule   Thu PM / Poster
Room   Ballroom B
Joint Body- and Surface-wave Inversion Applied to Geothermal Data
REITER, D., Weston Geophysical Corp., Lexington, MA, delaine@westongeophysical.com; FERRIS, A., Weston Geophysical Corp., Lexington, MA, aferris@westongeophysical.com; LEIDIG, M., Weston Geophysical Corp., Lexington, MA, mleidig@westongeophysical.com
We have adapted a joint inversion technique developed for regional-scale applications to the geothermal reservoir imaging problem. The inversion technique has several features that are important at the reservoir imaging scale, such as travel-time prediction methods that are not limited to layered structures or surface receivers, and 3-D nonlinear velocity tomography with geostatistical constraints. We have applied our joint inversion method to a data set from the Geysers geothermal area in northern California. The Geysers is the largest exploited geothermal reservoir in the world and represents an ideal test bed for more advanced passive imaging techniques. We have retrieved the archive of waveform data from the 22-station Geysers seismic network, which was initially deployed and operated by the Unocal Geothermal Division and is now provided through collaboration between the Calpine Corporation and the Northern California Earthquake Data Center (NCEDC). For a subset of events observed primarily in 2000, we picked body-wave phase arrivals and performed surface-wave dispersion analysis. We also developed a starting model prior to performing the inversion, based on previous studies and other information. Our paper will focus on the initial results from both the data analysis and application of the inversion technique.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Abbott, Robert
Schedule   Wed PM / Poster
Room   Ballroom B
Weights of evidence modeling of Site Conditions from approximately 7500 Vs30 measurements in Las Vegas Valley, Nevada
PANCHA, A., Optim SDS, Reno, NV, aashap@optimsds.com; ABBOTT, R. E., Sandia National Laboratories, Albuquerque, NM, reabbot@sandia.gov; PULLAMMANAPPALLIL, S., Optim Inc., Reno, NV, satish@optimsoftware.com; HELLMER, W. K., Clark County Department of Development Services, Las Vegas, NV, wkh@co.clark.nv.us
We model patterns of Vs30 (shear-wave velocity down to 30 meters) in Las Vegas Valley, Nevada, USA, using the Bayesian weights-of-evidence method. The training dataset consists of approximately 7500 measurements. This data, complied by Clark County, Nevada is a portion of a first-of-its-kind effort to map earthquake hazard class systematically through an entire urban area. Key evidential layers for the weights-of-evidence method include mapped geologic properties and topographic slope. The Vs30 measurements are first categorized into the three NEHRP classes (B, C, and D) found within the basin. We then create a posterior probability map for each site class by finding the positive and negative weights for the unique conditions present after combining the evidential layers. Within this basin, our preliminary model is successful 56% of the time for site class B (i.e. the measurement of NEHRP-B velocity where the posterior probability for NEHRP-B is the highest), 74% for NEHRP-C, and 82% for NEHRP-D. The low success rate for NEHRP-B is investigated. The modeled site conditions map is compared with a krigged map of the actual measured values and details of the evidence layers.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Tormann, Thessa
Schedule   Fri 2:15 PM / Oral
Room   Ballroom E
The Value of Micro-Seismicity Analysis for Probabilistic Seismic Hazard Assessment
TORMANN, T., ETH Zurich, Zurich, Switzerland, thessa.tormann@sed.ethz.ch; WIEMER, S., ETH Zurich, Zurich, Switzerland, stefan.wiemer@sed.ethz.ch; HARDEBECK, J., USGS Menlo Park, Menlo Park, CA,
One central question in probabilistic seismic hazard assessment is how much the abundant micro-seismicity can tell us about recurrence rates of the very infrequent large earthquakes. Here we especially focus on the strong heterogeneity observed in the Gutenberg-Richter b-value: is it meaningful to extrapolate local frequency-magnitude distributions observed for a magnitude range M1-M4 out to magnitudes in the scope of seismic hazard assessment, i.e. M6 and larger? b-values have been documented to vary strongly in space, with low b-values being associated with highly stressed areas, so-called asperities, rough (partly) locked patches on a fault plane, likely to participate in a larger earthquake, while high b-values are found in the less stressed creeping sections of faults, in geothermal and volcanic areas.Improving existing techniques of high-resolution cross-sectional b-value imaging, we systematically highlight along all Californian faults documented in the UCERF2 model regions of significantly anomalous b-values from highly linear frequency-magnitude distributions. We evaluate how the imaged regions of anomalously low b-values correlate with locations of historical M6+ earthquakes. We furthermore investigate the question whether temporal changes of b-values within well-defined and stable structures, such as the Parkfield asperity, can be related to changes in the loading of the fault. We develop several different approaches to constrain the validity of temporal changes seen in M6+ probabilities forecast by b-values. Our preliminary results suggest that indeed the micro-seismicity is in many regions able to accurately forecast the seismic hazard.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Schorlemmer, Danijel
Schedule   Fri 4:30 PM / Oral
Room   Ballroom E
Results from the Regional Earthquake Likelihood Models Experiment
SCHORLEMMER, D., University of Southern California, Los Angeles, CA, ds@usc.edu; ZECHAR, J. D., Swiss Seismological Service, Zurich, Switzerland, jeremy.zechar@sed.ethz.ch; WERNER, M., Princeton University, Princeton, NJ, mwerner@princeton.edu; GERSTENBERGER, M. C., GNS Science, Avalon, Lower Hutt, New Zealand, m.gerstenberger@gns.cri.nz; RHOADES, D. A., GNS Science, Avalon, Lower Hutt, New Zealand, D.Rhoades@gns.cri.nz; The RELM and CSEP Working Groups
One of the primary objectives of the Regional Earthquake Likelihood Models (RELM) working group was to formalize earthquake occurrence hypotheses in the form of prospective earthquake rate forecasts for California. RELM scientists developed more than a dozen time-invariant five-year forecasts for the period 1 January 2006-1 January 2011; they also outlined a performance evaluation method and provided a conceptual description of a Testing Center in which to perform this forecast experiments. Subsequently, researchers working within the Collaboratory for the Study of Earthquake Predictability (CSEP) have begun implementing Testing Centers in different locations worldwide, and the RELM forecast experiment-a truly prospective earthquake prediction effort-was conducted within the U.S. branch of CSEP. The experiment, designed to compare this set of forecasts is now complete. Here, we present the forecasts under evaluation and the results of this experiment. We also evaluate the sample of observed target earthquakes in the context of historical seismicity within the testing region. Finally, we discuss the implications of the results for California hazard assessment and for further experiments.
Session:Seismic Siting for Nuclear Power Plants
Presenter   Lin, Kuo-Wan
Schedule   Fri AM / Poster
Room   Ballroom B
Developing and Implementing a Real-Time Earthquake Notification System for Nuclear Power Plant Sites Using ShakeCast
LIN, K., U. S. Geological Survey, Denver, CO, klin@usgs.gov; WALD, J. D., U. S. Geological Survey, Denver, CO, wald@usgs.gov; ALTINYOLLAR, A., International Atomic Energy Agency, Vienna, Austria, A.Altinyollar@iaea.org; BEKIRI, N., International Atomic Energy Agency, Vienna, Austria, N.Bekiri@iaea.org; GODOY, A. R., International Atomic Energy Agency, Vienna, Austria, A.R.Godoy@iaea.org; AKE, J., U.S. Nuclear Regulatory Commission, Washington, DC, Jon.Ake@nrc.gov; KAMMERER, A., U.S. Nuclear Regulatory Commission, Washington, DC, annie.kammerer@nrc.gov
The IAEA International Seismic Safety Centre (ISSC) and the U. S. Nuclear Regulatory Commission (NRC), in collaboration with the U. S. Geological Survey (USGS), are developing and implementing a custom ShakeCast system for discovery, processing, and notification of real-time ground shaking information at nuclear power plant (NPP) sites. The custom system provides situational awareness and relevant information well tuned for the nuclear power community. ShakeCast is a freely-available, post-earthquake application that automatically retrieves earthquake shaking data from ShakeMap, compares intensity measures against users’ facilities, sends notifications of potential damage to responsible parties, and generates facility damage assessment maps and other Web-based products for emergency managers and responders. The custom system incorporates the USGS Production Distribution protocol as an additional pathway linking USGS earthquake information systems into a central repository of products. Significant attention is given to interdisciplinary data integration for improving rapid decision making, incorporating observation, prediction, and plant fragility and license information into real-time automated comparisons of estimated ground motions against plant-specific shut-down criteria and basic NPP damage estimations. For example, the automated ShakeCast report summaries exposed NPP sites and their shut-down criteria and vulnerability, charts significant historic earthquakes in the region and their impact at the sites, and relays societal information from DYFI and PAGER for added awareness of the regional situation. We present here the IAEA ShakeCast “use case” as part of the ISSC initial operating capability, with information available to the Agency’s Incident and Emergency Centre, for global NPP monitoring. The Atlas of Global ShakeMaps for nearly 5,500 historical earthquakes was used to compile a knowledge database of shaking history at existing and potential NPP sites.
Session:Assessment of Seismic Hazard from Paleoliquefaction Studies
Presenter   Olson, Scott
Schedule   Fri 11:15 AM / Oral
Room   Ballroom D
Clastic Dikes and Ground Fractures: Seismic or Not?
OBERMEIER, S. F., Emeritus USGS and EqLiq Consulting, Rockport, IN, sobermei@yahoo.com; OLSON, S. M., University of Illinois, Urbana, IL, olsons@illinois.edu; GREEN, R. A., Virginia Tech, Blacksburg, VA, rugreen@vt.edu
Frequently it is difficult to determine if clastic dikes and ground fractures in unconsolidated deposits are of seismic or nonseismic origin. Examples of clearcut seismic liquefaction origin are given first, with criteria for demonstrating origin, followed by examples of nonseismic or questionable origin.Typically, dikes from seismic liquefaction are tabular in plan view (except where the host is extremely soft), tend to taper or pinchout upsection, and are filled with cohesionless sediment with little or no clay; the filling in the dikes commonly shows evidence of fining upward, or of upward flow or concentrated flow of water, but can also be massive. Downward, the dike filling can be often traced to source beds at depth that liquefied.Assessing origin of ground fractures is often much more uncertain. Liquefaction-induced dikes and ground fractures are frequently found associated with one another, even where dikes are marginally developed. But it is frequently difficult to attribute a seismic origin to fractures not associated with elevated porewater pressure, making an area of needed research; this is especially true for sediments overlying karst terrain, commonplace in the central/eastern US. Still, some guidelines can assign likely origin. For example, fractures of shaking origin are often long, linear, and parallel. Weathering and/or desiccation typically produce a haphazard fracture pattern. Examples of ground fractures are shown for those clearly of seismic origin, from both shaking and from proximity to a fault. Equivocal examples are also shown.The field examples of dikes and fractures are from eastern Washington state, the central United States, coastal South Carolina, and the East Tennessee Seismic Zone. A basic lesson from our studies in these areas is that one must consider the possibility of special geologic or climatic conditions, which can produce features mimicking those of seismic origin.
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Zhang, Haijiang
Schedule   Thu 9:00 AM / Oral
Room   Ballroom E
Multiple Geophysical Imaging of the Utah Area Using Seismic and Gravity Data
ZHANG, H., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, hjzhang@mit.edu; MACEIRA, M., Los Alamos National Laboratory, Los Alamos, NM, mmaceira@lanl.gov; TOKSOZ, M. N., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, toksoz@mit.edu; BENSON, T., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, thomasrbenson@gmail.com; YU, H., Dept of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, haiyingyu2003@yahoo.com.cn
We developed a joint imaging algorithm that uses seismic body wave arrival times, surface wave dispersion measurements, and gravity data to determine three-dimensional (3D) Vp and Vs models. An empirical relationship mapping densities to Vp and Vs for earth materials is used to link them together. The joint inversion method takes advantage of strengths of individual data sets and is able to better constrain the velocity models from shallower to greater depths. In addition to linking densities to seismic velocities through an empirical relationship, we will also test linking them structurally based on a cross-gradient constraint. We applied this joint inversion method to determine the 3D Vp and Vs models of the Utah area, with a focus on the area around the Cove Fort geothermal field. We collected the seismic body wave arrival times from both the University of Utah Seismograph Stations (UUSS) regional network and EarthScope/USArray stations. The surface wave dispersion measurements are obtained from the ambient noise tomography study by the University of Colorado group using EarthScope/USArray stations. The gravity data for the Utah area is extracted from the North American Gravity Database managed by the University of Texas at El Paso. The resulting velocity models show that the transition zone between the Colorado Plateau to the east and the Great Basin to the west is associated with low velocity anomalies. Beneath the Cove Fort-Sulphurdale Geothermal Field, there is a strong anomaly of low seismic velocity, low gravity, high heat flow and high electrical conductivity.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Simmons, Nathan
Schedule   Wed AM / Poster
Room   Ballroom B
The LLNL-G3D global P-wave velocity model and its performance in seismic event location prediction
SIMMONS, N. A., Lawrence Livermore National Lab, Livermore, CA, simmons27@llnl.gov; MYERS, S. C., Lawrence Livermore National Lab, Livermore, CA, smyers@llnl.gov; JOHANNESSON, G., Lawrence Livermore National Lab, Livermore, CA, gardar@llnl.gov
We have constructed a global-scale model of P-wave velocity with an emphasis on improving travel time prediction at both regional and teleseismic distances simultaneously. The LLNL-G3D tomographic model is built within a spherical tessellation framework whereby irregular and discontinuous surfaces are explicitly represented. Fully 3-D ray tracing is employed for travel time prediction. The data consist of ~2.7 million P and Pn arrivals that are re-processed using our global multi-event locator known as BayesLoc. Bayesloc is a formulation of the joint probability distribution across multiple-event location parameters, including hypocenters, travel time corrections, pick precision, and phase labels. Modeling the whole multiple-event system results in accurate locations and an internally consistent data set that is ideal for tomography. Our recently developed inversion approach (called Progressive Multi-level Tessellation Inversion or PMTI) captures regional trends and fine details where data warrant. Using PMTI, we model multiple heterogeneity scale lengths without defining parameter grids with variable densities based on some user-defined criteria. We demonstrate the performance of our most recent model through comprehensive event location accuracy tests using several ground-truth (GT0-5) events throughout the world. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-465065
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Wilson, David
Schedule   Wed AM / Poster
Room   Ballroom B
Joint Receiver Function Imaging and Velocity Analysis
WILSON, D. C., USGS Albuquerque Seismological Laboratory, Albuquerque, NM, dwilson@usgs.gov
Measuring the relative arrival times of P-to-S converted phases in receiver functions allows for the estimation of local depth and average Vp/Vs ratio between the surface and a strong impedance contrast such as the base of the crust. This is typically done by stacking receiver function amplitudes of direct and reverberated modes at a single station over a range of crustal thicknesses (H) and Vp/Vs ratios. This is essentially a mapping of these amplitudes to the H-Vp/Vs plane, and the stacked trace amplitude will produce a local maximum at the best solution where the different modes add constructively.In this study, a novel variation on this velocity analysis technique is developed and applied to both synthetics and data. First, a multimode receiver function image is created using a reference P wave velocity model and a starting Vp/Vs ratio. For this starting model, lower crustal velocities are allowed to extend as a half-space, and then apparent Moho depths can be picked from the local maxima on each of the three multimode images produced. Using the initial velocity model, and these newly picked apparent Moho depths, the actual crustal Vp/Vs ratio can be calculated at each imaging point. Finally, the images are recomputed using this new velocity model.Mapping receiver function amplitudes from all stations to 3-dimensional space as a part of velocity analysis reduces the effects of dipping layers that are a major source of error in traditional receiver function velocity analysis. Rather than producing a 1-dimensional velocity model estimate beneath each station, a model is produced at each imaging point, thereby creating a multi-dimensional velocity model from which to compute a final receiver function image. This technique produces a velocity model that is a spatial mapping of crustal Vp/Vs values which can give insight toward regional crustal compositional variation.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Fitzenz, Delphine
Schedule   Fri 3:30 PM / Oral
Room   Ballroom E
A Bayesian Framework to Rank and Combine Candidate Recurrence Models for Specific Faults
FITZENZ, D. D., University of Évora, CGE, Evora, Portugal, delphine@uevora.pt; JALOBEANU, A., University of Évora, CGE, Evora, Portugal, jalobeanu@uevora.pt; FERRY, M. A., University of Évora, CGE, Evora, Portugal, matthieu@uevora.pt
Our three main objectives are 1) to show that earthquake geology data can be used quantitatively and in combination with historical and archeological catalogs of large earthquakes to constrain renewal models; 2) that working within a Bayesian framework allows to shift expert opinion upstream from model selection, leading to a better reproducibility; and 3) starting from a set of candidate recurrence models, to obtain the model or combination of models best representative of our level of knowledge of a given fault (for Probabilistic Seismic Hazard Assessment and for future tests of physical models).We use Bayesian inference for parameter and error estimation, graphical models (Bayesian networks) for modeling, and stochastic modeling to link cumulative offsets to coseismic fault slip.The COBBRA [1] method was initially developed to use cumulative offset data to further constrain and discriminate recurrence models built from historical and archaeological catalogs of large earthquakes. We present an extension of it that incorporates trench data [2]. The case study presented here is for the segment of the Dead Sea Fault in Jordan.We emphasize that 1) the time-variability of fault slip rate from cumulative offset is critical to constrain recurrence models, 2) the shape of the probability density functions (pdf) of the trench event ages is very important and in most cases can not be assumed Gaussian; 3) renewal models are in terms of intervals between consecutive earthquakes, not dates, and the algorithms should account for that fact; 4) maximum likelihood methods are possibly biased because of the small amount of data, do not restitute all relevant information, do not allow to compute the evidence of each model, and therefore can not lead to model combination or ranking. Finally, more work is needed to define proper priors. [1] Fitzenz, D. D., M. A. Ferry, and A. Jalobeanu (2010), Geophys. Res. Lett., doi:10.1029/2010GL044071 [2] Ferry et al (2011), BSSA in press
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Bisrat, Shishay
Schedule   Thu AM / Poster
Room   Ballroom B
3-D Seismic Attenuation Structure of the New Madrid Seismic Zone
BISRAT, S., CERI, University of Memphis, Memphis, TN, stbisrat@memphis.edu; DESHON, H., CERI, University of Memphis, Memphis, TN, hdeshon@memphis.edu
Tomography studies have been widely used to characterize seismic velocity and attenuation structure and investigate microseismic activity in the New Madrid Seismic Zone (NMSZ). Although seismic velocity images are available that incorporate good-quality data from the dense seismic network deployed in the last 15 years, there are no corresponding high-resolution 3-D attenuation images. We present new P-wave (Qp) and S-wave (Qs) attenuation structure of the New Madrid Seismic Zone (NMSZ) using the vertical and horizontal components of more than 400 small-magnitude (mb 2+) earthquakes derived using local earthquake tomography approaches. The microseismicity data include events recorded by the Portable Array for Numerical Data Acquisition (PANDA) experiment conducted in 1989-1991 and by the Cooperative New Madrid Seismic Network between 1995 and 2010. Whole path attenuation (t*) data are inverted in association with corresponding P and S-wave travel times to yield frequency-independent 3-D Qp and Qs structure. The t* calculation routinely takes into consideration source and path effects on the amplitude spectra of a seismogram when fitting the theoretical spectra to the observed spectra, but here we also include the local site effect on the amplitude. We explore the possible explanations for the observed heterogeneity in attenuation structure and compare the attenuation and associated velocity models to high-resolution earthquake locations and focal mechanism solutions to determine the interrelationship between fault structure, fluids, and seismogenesis along these intraplate faults.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Miner, Krystle
Schedule   Thu 10:30 AM / Oral
Room   Room 204/205
Seismic Site Amplification in Charleston, South Carolina: Observations
MINER, K. S., Department of Biology, College of Charleston, Charleston, SC, ksminer@edisto.cofc.edu; JAUME, S. C., Department of Geology, College of Charleston, Charleston, SC, jaumes@cofc.edu
The focus of this work is to observe seismic site response across Charleston County, South Carolina. Charleston lies on the Atlantic coastal plain and is underlain by approximately 1 km of post-Jurassic sediments, with a variety of Quaternary and man-made surficial deposits. We collected 30 minutes of ambient seismic noise using a CMG-6TD broadband seismometer at 72 sites. Sites were selected due to their proximity to existing geotechnical boreholes and with a goal of sampling the variety of surficial geology. From this ambient noise data we produced H/V spectral ratios in order to quantify the preferred resonance frequency for each site. High frequency resonances were expected to vary significantly between sites and fall within a range of 2-10 Hz, based upon a previous geotechnical site response study (Chapman et al., 2008). Surprisingly, most of the sites showed little variation in peak resonance frequency, with the majority of sites showing strong resonance in the 1-2 Hz range. Those sites that did not show a 1-2 Hz resonance peak were located in the far north of our study area and on older geological materials. We also observed that sites on artificial fill resonate at higher amplitudes than sites on natural geological surfaces, but without a change in peak frequency. In order to confirm these observations, we established a 3 element array across the Charleston peninsula, with two sites on Quaternary surfaces of different ages and one site on artificial fill. Vertical spectral amplitudes did not differ between the three sites for frequencies up to 4 Hz. This shows that the 1-2 Hz site resonance is purely a result of variation in the amplitude of the horizontal motion. This result confirmed that the amplitude difference in the 1-2 Hz resonance between artificial fill and older materials is stable and likely not a result of variations in input ground motion.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Butler, David
Schedule   Wed PM / Poster
Room   Ballroom B
Scenario-Based Seismic Hazard Assessment of Tianshui, Gansu Province, China
BUTLER, D. T., University of Kentucky, Lexington, KY, david.butler@uky.edu; WANG, Z., Kentucky Geological Survey, Lexington, KY, zmwang@uky.edu; WOOLERY, E. W., University of Kentucky, Lexington, KY, woolery@uky.edu; WANG, L., Lanzhou Institute of Seismology, Lanzhou, Gansu Province, China, wanglm@gssb.gov.cn; YUAN, Z., Lanzhou Institute of Seismology, Lanzhou, Gansu Province, China, zhonxiayuan@hotmail.com; LU, Y., Lanzhou Institute of Seismology, Lanzhou, Gansu Province, China, yuxial@163.com
Tianshui, the second largest city in the Gansu Province (population 3.5 million), is located in an active tectonic accommodation zone along the Tibetan Plateau’s northeastern margin. The West Qinling North Boundary Fault is a major structure in this zone. It has a measured slip rate of 2.4 mm/yr and is the most significant seismic source for the urban area. Historical records show that between 134 AD and 1987 the city has experienced 32 strong earthquakes with intensity 4 or greater. The epicenter for the M7.5 March 23, 734 AD event, which killed approximately 4,000 people, occurred within the present urban boundaries. The city is underlain by between 10 and 50 meters of loess and alluvium. The dynamic properties of these sediments were measured at 18 sites with surface and borehole seismic methods. Two composite-source acceleration time histories for an M7.5 earthquake with epicentral distances of 16 and 34 km were generated for one-dimensional ground-motion analysis. Results showed amplifications and frequencies ranging between 2 and 7, and 2.2 and 12.6 Hz, respectively.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Moore-Driskell, Melissa
Schedule   Thu 9:15 AM / Oral
Room   Ballroom D
3D Double Difference Velocity Tomography of the Costa Rican and Nicaraguan Subduction Zones
MOORE-DRISKELL, M. M., CERI-University of Memphis, Memphis, TN, mmdrskll@memphis.edu; DESHON, H., CERI-University of Memphis, Memphis, TN, hdeshon@memphis.edu
Previous seismic studies show that the Nicaragua/Costa Rica segment of the Middle America subduction zone has seismogenic zone characteristics that are strongly dependent on plate structure, temperature, and fluid-related processes. The data in this study come from a quality-controlled integration of amphibious datasets from the Osa and Nicoya networks collected as part of CRSEIZE (PIs. S. Schwartz/L. Dorman) and the Jaco/Quepos, Nicaragua, and Nicaragua outer-rise networks collected as part of the SFB 574 program (PIs. E. Flueh/W. Rabbel). The combined networks provide ~600 km of along-strike coverage of the seismogenic zone. We use the double difference local earthquake tomography approach, utilizing catalog derived absolute and differential times plus waveform cross-correlation derived differential times. Results show improved hypocentral locations of seismogenic zone earthquakes and compressional and shear velocity structure of the seismogenic zone extending from Nicaragua through central Costa Rica. Highest resolution occurs within the shallow seismogenic zone, but we also image the nose of the forearc mantle wedge. Compressional velocity images appear broadly consistent with previous studies. We find that the updip limit of seismogenic zone microseismicity is variable and may be located closer to trench in Nicaragua. The interplate interseismic microseismicity occurs near the expected continental Moho intersection with the subducting plate interface, and comparison with recent subduction tremor, which occurs downdip of microseismicity, suggests that the tremor may be a better proxy for the downdip limit of rupture during major earthquakes. Results provide insight into the role of fluids within the seismogenic zone and shallow forearc mantle.
Session:Guide to Sustainable Seismographic Networks
Presenter   Nyblade, Andrew
Schedule   Fri 9:00 AM / Oral
Room   Ballroom C
Building Sustainable Networks in Africa: Experiences from AfricaArray
NYBLADE, A. A., Penn State University, University Park, PA, andy@geosc.psu.edu; DURRHEIM, R., University of the Witwatersrand, Johannesburg, South Africa, rdurrhei@csir.co.za; DIRKS, P., James Cook University, Cairns, Queensland, Australia, paul.dirks@jcu.edu.au; GRAHAM, G., Council for Geoscience, Pretoria, South Africa, gerhardg@geoscience.org.za
AfricaArray (www.africaarray.org) is a 20-year initiative in the geosciences (Earth, Atmospheric and Space sciences) to meet the New Partnership for Africa's Development (NEPAD) requirements for continent-wide co-operation in human-resources development and capacity building. Although the long-term vision for AfricaArray is to support capacity building in all geoscience fields, AfricaArray began with a focus on solid earth geophysics, and seismology in particular, to 1) maintain and develop existing geophysical training programs, 2) promote geophysical research, 3) improve diversity in the geophysical workforce and, 4) establish a network of seismic observatories to obtain data for investigating scientific targets of economic, societal and academic importance. The establishment of an observatory network was also considered essential for developing a support system through which to develop the African science community by providing data for student research, fostering data sharing, and developing collaborative projects. The AfricaArray seismic network now includes 39 broadband stations in 15 countries spanning eastern, southern and western Africa. There have been many challenges over the past 6 years in developing this network, and there have been a number of missed opportunities to further expand the network and to help national network operators build and maintain their own networks. In this paper, experiences from AfricaArray will be shared that provide examples of how a guide to sustainable networks would have been valuable in the African context and would have helped national network operators better plan for the construction, operation and maintenance of their seismic networks.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Paschall, Anthony
Schedule   Wed PM / Poster
Room   Ballroom B
Comparing the Observed and Predicted Linear Site Effect From the April 2008 Mount Carmel IL M5.2 Earthquake, Central United States
PASCHALL, A. M., University of Kentucky, Lexington, KY, ampasc2@uky.edu; WOOLERY, E. W., University of Kentucky, Lexington, KY, woolery@uky.edu; STREET, R. L., , Hermosa, SD, bhrstreet@yahoo.com
Eighteen observations from the April 18, 2008 M5.2 Mt Carmel, IL earthquake constrain site effects predicted by empirical NEHRP V30 and linear 1-D calculations, as well as the Nuttli-Herrmann (1984) semi-empirical predictive relationship. Dynamic site properties for the sediment overburden and bedrock were measured using seismic (SH-wave) refraction/reflection surveys. The observed amplification factor was defined by comparing free-field peak velocity measurements and recent predictive relationships for the central and eastern United States B/C boundary. Ideally, corrected PGV’s will converge to one. The mean residual 0.8 (± 0.4) from linear 1-D corrections exhibited better convergence than the mean residual 4.2 (± 1.7) of the NEHRP corrections. The linear 1-D and Nuttli-Herrmann (0.6, ± 0.3) corrections were similar.
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Bailey, Iain
Schedule   Thu 9:30 AM / Oral
Room   Ballroom E
Investigation of Vs and Density Structure Beneath the Colorado Plateau Based on Gravity, Receiver Function and Surface Wave Data
BAILEY, I. W., University of Southern California, Los Angeles, CA, iwbailey@usc.edu; MILLER, M. S., University of Southern California, Los Angeles, CA, msmiller@usc.edu; LEVANDER, A., Rice University, Houston, TX, alan@rice.edu; LIU, K., Rice University, Houston, TX, kl4@rice.edu
We present results from joint inversions of surface wave and receiver function data to compute Vs in the crust and upper mantle beneath the Colorado Plateau, then compare gravity observations with predictions based on the seismic results to constrain density. For the joint inversions, we use codes from the Computer Programs in Seismology package (Herrmann & Ammon, 2002) applied to a data set of ~3,000 P-receiver functions and gridded Rayleigh wave phase velocities for 18 periods, both based primarily on USArray data. Simultaneously solving for both data sets constrains broad changes in absolute velocity as well as sharp discontinuities in a 1-D Vs profile. We perform inversions for each receiver function, then use a Gaussian weighted spatial averaging method to estimate a 3-D Vs model and its uncertainty. Our results show a well defined Moho, with a sharp increase in crustal thickness from west to east at the western edge of the plateau and a further, more gradual increase into the Rocky Mountains. A high velocity anomaly is observed in the range 75 - 100 km below the plateau, getting thicker to the north-northeast. Using empirical scaling relations and a constant Poisson ratio, we convert the seismic results to density then compare the predicted Bouguer anomaly with that obtained from the US gravity database. The predicted anomaly shows a strong correlation with seismic variations in the mantle that is not reflected in the observed anomaly. Using the seismic results to define the Moho and lithosphere-asthenosphere boundary, then adjusting the density scaling relations separately for the crust, lithospheric mantle and asthenosphere, we obtain an improved fit using constant density for the asthenosphere and enhanced density contrast across the Moho. We examine this density structure in relation to support of the plateau’s uniformly high elevations (> 1.5 km) and previously suggested explanations for its uplift.
Session:Seismotectonics and Hazards of Active Margins in the Circum-Caribbean Sea and Eastern Pacific Ocean
Presenter   Hellweg, Margaret
Schedule   Wed 11:15 AM / Oral
Room   Ballroom D
Earthquake Magnitudes in Northern California
HELLWEG, M., UC Berkeley Seismological Lab, Berkeley, CA, peggy@seismo.berkeley.edu; OPPENHEIMER, D. H., United States Geological Survey, Menlo Park, CA, oppen@usgs.gov
Earthquake magnitude, hypocentral location, and origin time are the most representative event characteristics used for hazard and seismicity evaluations. Over the past decade the way different types of magnitudes are assigned to Northern California events has changed with the evolving integration of earthquake reporting operations at UC Berkeley and USGS Menlo Park. Since 1996 earthquake magnitude has been assigned with priority based on event size: for events with duration magnitude Md>3, the computation of a local magnitude (ML) is attempted. If ML is successfully produced, it becomes the authoritative magnitude for an event. If ML>3.5, we attempt a moment tensor and concomitant moment magnitude (Mw). If the variance reduction of the moment tensor inversion is greater than 40%, then Mw becomes the authoritative magnitude. Thus, a request for catalog information will retrieve events with a variety of magnitude types. In addition, since June 2009, ML is calculated using a new suite of log A0 and station adjustments valid throughout the state and from amplitudes that are measured using time domain simulation of Wood Anderson records. Work is now proceeding to integrate the UC Berkeley and NCSN catalogs from the years prior to 1996. In this process official magnitudes for events may change, with the UC Berkeley ML supplanting the NCSN Md and Mw supplanting ML should it be possible to compute Mw using a regional moment tensor analysis method. In the end, we will assign the most reasonable existing magnitude estimates to historical earthquakes, including teleseismic magnitude estimates from the NEIC. The results of this work may have implications for estimates of seismicity rates and hazard.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Powell, Christine
Schedule   Thu AM / Poster
Room   Ballroom B
Complex Faulting and Velocity Structure Within the New Madrid Seismic Zone
POWELL, C. A., CERI, The University of Memphis, Memphis, TN, capowell@memphis.edu; DESHON, H. R., CERI, The University of Memphis, Memphis, TN, hdeshon@memphis.edu; LANGSTON, C. A., CERI, The University of Memphis, Memphis, TN, clangstn@memphis.edu
Earthquakes in the Cooperative New Madrid Seismic Network catalog for the period 1995-2010 are relocated using 3D Vp and Vs models determined using the double-difference inversion method (tomoFDD). The dataset contains the most accurate New Madrid seismic zone (NMSZ) earthquake locations to date and delineates interesting fault complexity associated with the four major arms of seismicity. The major arms include two NE trending, right-lateral strike-slip faults (the Cottonwood Grove–Blytheville Arch (CGBA) fault and the north arm) offset by a NW trending reverse fault (Reelfoot fault (RF)). A west arm trends EW from the northern termination of the RF. The simple structural model of two strike-slip faults offset by a left-stepping reverse fault is complicated by the extension of the RF south of its intersection with the CGBA. Our relocations reveal distinct differences between the northern portion of the RF (north of the CGBA) and the southern portion. In the northern portion, earthquakes occur in distinct clusters that delineate a SW dipping fault plane extending from about 6 to 14 km depth. Two distinct, parallel clusters of earthquakes are often observed. Northern RF seismicity is associated with low Vp/Vs ratios produced by low Vp and high Vs anomalies. South of the CGBA intersection, seismicity defining the RF becomes shallower and more dispersed. This portion of the southern RF is associated with swarm activity and low Vp and Vs anomalies attributed to fractured, fluid filled rocks. The strike-slip northern arm consists of two parallel, near-vertical faults. Individual fault segments within the RF and CGBA arms are identified using a pattern recognition method that reconstructs the 3D structure of a fault network using the spatial locations of earthquakes. This is a first step in the analysis of fault interaction using 3D boundary element modeling and stress transfer software.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Wang, Feng
Schedule   Wed AM / Poster
Room   Ballroom B
Precise Verification of Numerical Simulations for Tomographic Application
WANG, F., University of Southern California, Los Angeles, CA, fengw@usc.edu; ELY, G. P., University of Southern California, Los Angeles, CA, gely@usc.edu; JORDAN, T. H., University of Southern California, Los Angeles, CA, tjordan@usc.edu
Earthquake simulations in 3D structures are currently being used for forward prediction of ground motions, imaging of sources, and structure refinement (full-3D tomography). The computational platform for such numerical simulations requires the accurate location of sources and receivers within the computational grid; the flexibility to represent geological complexities, such as topography, non-planar faults, and other distorted surfaces; and the facility to calculate 3D Fréchet kernels for source and structural perturbations. Precise measurements of the generalized seismological data functionals (GSDF) are employed to characterize frequency-dependent numerical effects (e.g., grid dispersion) and model complexities using two numerical methods: the support operator rupture dynamics (SORD), which has second-order accuracy, and a well-tested, fourth-order, finite-difference method (AWP-ODC). Combining the SORD distortable-mesh capability with GSDF measurements, we quantify the importance of topography and sphericity for regional tomographic applications. We have computed synthetic seismograms for earthquakes in Southern California for 3D Cartesian-mesh models with and without topography, and we have verified the travel-times and amplitudes of the synthetics by cross-comparison with those computed by AWP-ODC. We have implemented in SORD the scattering-integral method to calculate frequency-dependent 3D structural kernels, and we illustrate how they can provide a physical understanding of seismic wave interference, excitation, and amplification in the sedimentary basins of Southern California.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Park, Junghyun
Schedule   Thu AM / Poster
Room   Ballroom B
Relocation of Earthquakes in the New Madrid Seismic Zone: 1D Velocity Structure and Geometry of Seismogenic Fault
PARK, J., Southern Methodist University, Dallas, TX, junghyunp@smu.edu; LEE, J. M., Kyungpook National University, Daegu, Korea, jung@knu.ac.kr; KIM, W., Gyeongsang National University, Jinju, Korea, wookim@gnu.ac.kr; KIM, W. Y., Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, wykim@ldeo.columbia.edu
Determination of accurate hypocentral parameters including, latitude, longitude, focal depth and origin time, are critical to earthquake seismology. In order to determine the hypocentral parameters, there are many approaches and associated software packages such as HYPO-71, HYPOELLIPSE, LocSAT, VELEST and HYPOSAT. These algorithms, however, can be affected by non-uniqueness, associated with the assumption of the initial velocity model. GA-MHYPO, on the contrary, estimates hypocentral parameters for local earthquakes independent of the initial velocity model by utilizing the genetic algorithm (GA) to find an optimal 1-D velocity model. Using GA-MHYPO, we have relocated earthquakes that occurred in the New Madrid Seismic Zone (NMSZ) in the central United States from October 1989 to August 1992. The goal is to delineate possible fault plane(s) and to determine a 1-D velocity structure for the NMSZ. A total of 502 earthquakes recorded by 40 PANDA (Portable Array for Numerical Data Acquisition) stations have been used in the relocation study. The new locations reduce the rms errors by 20 % and 2.3 km in depth (deeper). The new epicenters have an average difference of 0.7 km in latitude, 0.8 km in longitude, relative to those determined previously using HYPOELLIPSE. To estimate a single 1-D velocity model, the new earthquake locations were used in a traveltime inversion, employing two-point ray tracing, P-wave arrivals for 233 events and S-wave arrivals for 216 events. The resulting eight layer velocity model consisted of a 2-km-thick surface layer with Vp=2.14 km/s and Vs=1.26 km/s followed by seven 2-km-thick layers with Vp increasing from 5.36 to 6.74 km/s and Vs increasing from 3.12 to 3.90 km/s. The fault plane that represents the Cottonwood Grove Fault is estimated by applying a linear regression to the earthquake locations. In order to make a closer investigation into the geometry, we are presently estimating the fault plane solutions of these even
Session:Assessment of Seismic Hazard from Paleoliquefaction Studies
Presenter   Green, Russell
Schedule   Fri 11:30 AM / Oral
Room   Ballroom D
Clastic Dikes in the Ancient Glacial Lake Missoula Flood Sediments
GREEN, R. A., Virginia Tech, Blacksburg, VA, rugreen@vt.edu; OBERMEIER, S. F., Emeritus USGS and EqLiq Consulting, Rockport, IN, sobermei@yahoo.com; OLSON, S. M., University of Illinois, Urbana, IL, olsons@illinois.edu; CARPENTER, C. K., University of Michigan, Ann Arbor, MI, rugreen@umich.edu; GYURISIN, S. J., Virginia Tech, Blacksburg, VA, sjgyuri@vt.edu; HARRINGTON, T. J., Virginia Tech, Blacksburg, VA, tjharr87@vt.edu; HIGGINS, N., Virginia Tech, Blacksburg, VA, higginnj@vt.edu
Uncertainty exists regarding the formative mechanism of the clastic dikes found in the ancient Glacial Lake Missoula flood sediments in eastern Washington and western Idaho. Most commonly their origin has been hypothesized to be related to either seismic or flooding events. The objective of the study presented herein is to examine the flooding-origin hypothesis in more depth. Central to this hypothesis is that the dikes resulted from hydraulic fracturing as the hydraulic heads of the rapidly placed, turbid flood water and ground water equilibrated. Inherently, the silt sheets that line the walls of the dikes are then actually filter cakes that allowed large seepage forces to develop, and hence, the hydraulic fracturing to occur. To test this hypothesis, the grain size characteristics of samples collected from features and host sediments were evaluated using filter cake formation criteria for the design of slurry trenches and earthen dam filters. Additionally, filter cake permeability tests were performed wherein water with silt sheet material suspended in it was permeated up through host sediments collected from the clastic dike sites. The purpose of these tests was to see whether the host sediments would filter out the suspended silt sheet material as the water flowed through it, with a filter cake thus forming. The results from the grain size criteria evaluations were largely consistent with field observations. The authors hypothesize that the few miss-predictions are due to the conservatism inherent to the engineering design criteria for slurry trenches and dams. The filter cake permeability tests yielded results that were even more consistent with field observations than the grain size criteria evaluations. Accordingly, the results from both the grain size criteria evaluations and the filter cake permeability tests give credence to the hypothesis that the origin of the dikes is related to flooding events, not seismic events.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Herrmann, Robert
Schedule   Wed 3:00 PM / Oral
Room   Room 204/205
An Investigation of Eastern North America Ground Motion Scaling Relations Using Recent Earthquake Data
HERRMANN, R. B., Saint Louis University, St. Louis, MO, rbh@eas.slu.edu
Significant additions to the ENA ground motion scaling data sets were made possible in 2010 by the recording of earthquakes in Quebec, Oklahoma and Arkansas. The Oklahoma earthquake was near Oklahoma, City which has had a swarm of earthquakes starting in the summer of 2009. The activity picked up in January, 2010 and NetQuake accelerometers were deployed with the assistance of the Oklahoma Geophysical Observatory and the USGS. In addition the Transportable Array component of USArray moved to the eastern Great Plains. The Mw=4.33 and 4.15 earthquakes are the first well recorded earthquakes in this part of Oklahoma since the 1953, El Reno, Oklahoma earthquake.An earthquake swarm northeast Little Rock, Arkansas has also provided well recorded data sets. The quality of the available permitted broadband moment tensor inversion for source mechanism, depth and Mw as well as the high frequency data which are compared to existing ground motion scaling models in the 50 – 1000 km distance and Mw 4 – 5.3. These new data sets permit an investigation of the effects of regional variations of wave propagation and source mechanism on high frequency ground motions.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Mostafanejad, Akram
Schedule   Thu AM / Poster
Room   Ballroom B
Variation of Seismic b-Value in the New Madrid Seismic Zone
MOSTAFANEJAD, A., University of Memphis, Memphis, TN, mstfnjad@memphis.edu; POWELL, C. A., University of Memphis, Memphis, TN, capowell@memphis.edu; LANGSTON, C. A., University of Memphis, Memphis, TN, clangstn@memphis.edu
The spatial variation of seismic b-value is mapped for the New Madrid seismic zone using local events occurring between 1995 and 2010. A region of high b-value (about 1.9) is found in the northern part of the Reelfoot fault. By performing probability tests and following different procedures to obtain the result, we show that the anomalously high b-value is not a processing artifact and is statistically significant. We attribute the b-value anomaly to creep behavior on the northern segment of the Reelfoot fault. Creep behavior is suggested by recently discovered tremor and by the presence of quartz-rich rock as indicated by low Vp/Vs ratios detected in a local earthquake tomography study. Since quartz is a weak mineral, ductile, creeping behavior could be facilitated at depth resulting in generation of earthquakes. An area of lower b-value is found for the southern part of the Reelfoot fault, suggesting that the occurrence of small earthquakes is less frequent there than in the northern segment. The southern segment is not associated with low Vp/Vs ratios and may not be experiencing creep behavior.
Session:Earthquake Triggering and Induced Seismicity
Presenter   Sullivan, Brendan
Schedule   Wed 2:30 PM / Oral
Room   Ballroom D
Delayed Triggering of Earthquakes by Multiple Waves Circling the Earth
SULLIVAN, B. L., Georgia Institute of Technology, Atlanta, GA, brendan.sullivan@eas.gatech.edu; PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng@gatech.edu; WU, C., Georgia Institute of Technology, Atlanta, GA, chunquanwu@gatech.edu; AIKEN, C., Georgia Institute of Technology, Atlanta, GA, chastity.aiken@eas.gatech.edu
It is well known that direct surface waves of large earthquakes are capable of triggering shallow earthquakes and deep tremor at long-range distances. However, it is not clear whether multiple waves circling the earth could also trigger seismic events. Here we conduct two studies to search for evidence of such triggering. In the first study, we systematically search for remotely triggered microearthquakes near the Coso Geothermal Field following the 2010 Mw 8.8 Chile earthquake. We find a statistically significant increase of microearthquakes in the first few hours after the Chile mainshock. The apparently delayed triggering of these earthquakes does not follow the Omori-law decay with time since the Ml = 3.5 event occurred during the large-amplitude Love waves. Instead, the earthquakes are better correlated with the first three groups of multiple surface waves (G1-R1, G2-R2, and G3). This observation provides an alternative explanation of delayed triggering of microearthquakes at long-range distances, at least in the first few hours after large-magnitude earthquakes.In the second study, we examine the aftershock activities of 20 magnitude-8-or-higher earthquakes that are capable of producing surface waves circling the globe repeatedly. We compute the magnitude of completeness for each sequence, and stack all the sequences together to compute both the seismicity and moment rates. Our preliminary results suggest that there is some moderate increase of aftershock activity after a few hours when the surface waves return to the epicentral region. But we could not rule out the possibility that such an increase is purely due to random fluctuations of aftershocks, or caused by missing aftershocks in the first few hours after the mainshock. In our next step, we will evaluate whether such an increase is statistically significant, and examine continuous waveform data of selected sequences to obtain a better understanding of the multiple surface waves and aftershock activity.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Rigsby, Christopher
Schedule   Thu AM / Poster
Room   Ballroom B
Investigation of the mb_Lg Magnitude Using Recent USArray TA Waveforms
RIGSBY, C. M., Saint Louis University, St. Louis, MO, christopher.m.rigsby@gmail.com; HERRMANN, R. B., Saint Louis University, St. Louis, MO, rbh@eas.slu.edu
Nuttli (1973) introduced the mbLg magnitude scale tailored to observed attenuation of the Lg phase in the eastern U.S. To develop this scale, Nuttli used a sparse set of photographic recordings from WWSSN short-period vertical seismographs to develop this scale. A modification by Nuttli (1986) adapted the formula for use with different coefficients of anelastic attenuation. The mb_Lg module used by NEIC uses the Nuttli (1986) formulation. The October, 2010, of an Mw=4.3 earthquake in Oklahoma and Mw 3.8 in Arkansas earthquake in Akransas within or adjacent to the current USArray Transportable Array deployment permits a detailed examination of the applicability of the mb_Lg definition to propagation paths north into the central Great Plains and south into the Gulf Coastal Plain. In addition the important issue of the relationship of the mb_Lg magnitude to Mw will be addressed for central U.S. Earthquakes with 3.5 < Mw < 5.3.
Session:Creative Wavefield Recording and Analysis
Presenter   Rademacher, Horst
Schedule   Fri 11:45 AM / Oral
Room   Ballroom E
A New Concept for Multidisciplinary Cabled Ocean Bottom Systems: the Marmara Sea Network
GURALP, C. M., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, cguralp@guralp.com; TUNC, S., Kocaeli University, Kocaeli, Turkey, stunc@sentezmuhendislik.com; ADA, S., Sentez Earth and Structure Engineering Ltd., Instanbul, Turkey, ; PEARCEY, C., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, ; RADEMACHER, H., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom,
Probably the single most limiting factor in deploying multidisciplinary cabled ocean bottom systems is cost. The current layouts and designs call for the use of ROV to deploy sensors and connect them to the network. They also include multiple nodes on the sea floor, at each of which clusters of instruments are connected to the network cables. These nodes add to the complexity of installations, because they usually require wet connections. Here we present a new concept for a cabled ocean bottom observatory network. We show data from its first deployment in the Marmara Sea (Turkey). Although our system is much simpler to install than current designs, it is fully capable of collecting and telemetering multidisciplinary data from the ocean floor in real-time at substantially lower costs.The core of our concept is that each cluster of instruments on the ocean bottom has its own cable and shore station. We thereby eliminate the need for costly nodes. This concept of "one sensor - one cable" also increases the reliability of the network as a whole, because the data of only one station are compromised, if a cable is cut or damaged. In addition, connections of the sensors to their respective cables are made before deployment on land, thus eliminating the need to use underwater vehicles. We installed the first network based on this concept in 2010 in the Marmara Sea. It consists of 5 ocean bottom stations. Its primary function is to monitor the seismic activity along the segment of the North Anatolian Fault which crosses the Marmara Sea. Each station is equipped with a broadband velocity sensor (CMG-3T), an accelerometer (CMG-5T), digitizer, a hydrophone, a differential pressure gauge, an acoustic doppler profiler, a sensitive thermometer and a camera. More equipment can be added if necessary. The stations are deployed up to 20 km from the coast in water depth of up to 1300 m. Their data are added in real-time to the existing land based seismic networks in Turkey.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Ramirez-Guzman, Leonardo
Schedule   Wed 4:15 PM / Oral
Room   Ballroom C
Central United States Earthquake Ground Motion Simulation Working Group: The 1811-1812 New Madrid Earthquake Sequence.
RAMIREZ-GUZMAN, L., U.S. Geological Survey, Golden, CO, lramirezguzman@usgs.gov; GRAVES, R. W., U.S. Geological Survey, Pasadena, CA, rwgraves@usgs.gov; OLSEN, K. B., San Diego State University, San Diego, CA, kbolsen@sciences.sdsu.edu; BOYD, O. S., U.S. Geological Survey, Memphis, TN, olboyd@usgs.gov; HARTZELL, S., U.S. Geological Survey, Golden, CO, shartzell@usgs.gov; NI, S., URS Corporation, Los Angeles, CA, stone_ni@urscorp.com; SOMERVILLE, P. G., URS Corporation, Los Angeles, CA, paul_somerville@urscorp.com; WILLIAMS, R. A., U.S. Geological Survey, Golden, CO, rawilliams@usgs.gov; ZHONG, J., San Diego State University, San Diego, CA, zhong@projects.sdsu.edu
We present a summary and analysis of simulations of hypothetical earthquake scenarios in the New Madrid Seismic Zone (NMSZ). This work is conducted as a collaborative effort between three simulation groups with different numerical modeling approaches (finite differences and finite elements) and computational capabilities. We use a recently developed community velocity model of the region (Ramirez-Guzman et al., 2010), three different kinematic source generation approaches (Graves et al., 2010; Liu et al, 2006; Hartzell et al., 1996) and one approach where sources are generated using dynamic rupture simulations (Olsen et al., 2009). In order to test the velocity structure and cross-verify the different simulation platforms, we compute synthetic ground motion for the Mw=5.4 April 14 2008 Mt. Carmel (IL) earthquake. We establish an acceptable goodness of fit among simulations and observed records by evaluating different metrics of seismological and engineering interest. Then, we simulate a set of hypothetical earthquake scenarios with different magnitudes (Mw 7-7.7) for three faults associated with the seismicity trends in the NMSZ: the Axial fault or Southern segment, the Reelfoot fault, and the Northern segment. Our results will have an impact on our understanding of: 1) a plausible range of magnitudes for the three main shocks of the 1811-1812 sequence, 2) estimates of the range of ground motions including peak ground acceleration and velocity, and Mercalli intensities in the region, and 3) effects on wave propagation of geologic structures, such as the Reelfoot Rift and the Mississippi embayment.
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Chang, Junyong
Schedule   Thu PM / Poster
Room   Ballroom B
Joint Inversion of Surface-Wave Dispersion and First-Arrival Times for the Determination of Shallow P- And S-Velocity Structure
CHANG, J., Saint Louis University, St. Louis, MO, junyongchang@gmail.com; HERRMANN, R. B., Saint Louis University, St. Louis, MO, rbh@eas.slu.edu; CROSSLEY, D. J., Saint Louis University, St. Louis, MO, crossleydj@gmail.com
The determination of shallow shear-wave velocity structure using surface-wave techniques is limited because of the inherent insensitivity of fundamental mode surface-wave dispersion to detailed structure, especially at depth. In the absence of independent estimates of layer thicknesses that could overcome this problem, we investigate the use of joint inversion of first arrivals together with Love- and Rayleigh-wave phase-velocity dispersion obtained using hammer sources and a linear geophone spread. The advantages of this approach are that the first-arrival data constrain layer thicknesses and halfspace velocity and the use of the P-wave data avoids reliance on an assumed Vp/Vs ratio for the inversion of the Rayleigh-wave data. Our initial implementation builds on the existing surface-wave inversion procedure contained in Computer Programs in Seismology. We apply this procedure to data sets acquired at eight sites in the metropolitan St. Louis area. The data were acquired along 72 meter long spreads using vertical and transversely oriented 4.5 Hz geophones and vertical and transverse hammer sources. 
Session:Seismic Sources and Parameters
Presenter   Liu, Qiming
Schedule   Wed AM / Poster
Room   Ballroom B
Dynamic Rupture Modeling of the 2008 Wenchuan Earthquake
LIU, Q., University of California, Santa Barbara, CA, qliu@eri.ucsb.edu; JI, C., University of California, Santa Barbara, CA, ; MA, S., San Diego State University, San Diego, CA, ; ARCHULETA, R. J., University of California, Santa Barbara, CA,
Both finite fault kinematic inversions based on different datasets (seismogram, GPS, InSAR) and field studies (surface rupture observations) suggested a complicated rupture process of the 2008 Mw 7.9 Wenchuan earthquake, particularly its initial stage. The rupture started and unilaterally propagated northeast on the low angle Pengguan fault, which only released 27% of total seismic moment. Rupture on the high angle Beichuan fault initiated as late as 17 s and 40 km northeast of the epicenter. Rupture on the Beichuan fault propagated bilaterally — to the northeast and also southwest back towards the epicenter. While fault geometry, including the varying dip angles of the segments is likely to influence the rupture, stress heterogeneity, both in magnitude and direction over the two faults, is almost certain to exert a significant importance in controlling the rupture. Here we use a 3-D finite element code to forward model such an complicated dynamic rupture interaction. We simplify the fault geometry as two planar rectangular faults, with dipping angles of 50 degree (upper one, representing Beichuan fault) and 30 degree (lower one, representing Pengguan fault), intersecting at 12 km depth. Inferred from the kinematic slip model, we use a simple patchy initial stress distribution to test various combinations of stress amplitude and material properties capable of reproducing the kinematic inversion results for the source description. The dynamic rupture simulation could shed some light on the background tectonic movement between the Tibet plateau and the Sichuan Basin as well as lower and upper crust interaction.
Session:The Seismo-Acoustic Wavefield
Presenter   Wurman, Gilead
Schedule   Fri AM / Poster
Room   Ballroom B
The Effect of Sonic Booms on Earthquake Warning Systems
WURMAN, G., Seismic Warning Systems, Inc., Scotts Valley, CA, gwurman@seismicwarning.com; HAERING, JR., E. A., NASA Dryden Flight Research Center, Edwards, CA, edward.a.haering@nasa.gov; PRICE, M. J., Seismic Warning Systems, Inc., Scotts Valley, CA, mprice@seismicwarning.com
Several aerospace companies are designing quiet supersonic business jets for service over the United States. These aircraft have the potential to increase the occurrence of mild sonic booms across the country. This leads to interest among earthquake warning (EQW) developers and the general seismological community in characterizing the effect of sonic booms on seismic sensors in the field, their potential impact on EQW systems, and means of discriminating their signatures from those of earthquakes.The SonicBREWS project (Sonic Boom Resistant Earthquake Warning Systems) is a collaborative effort between Seismic Warning Systems, Inc. (SWS) and NASA Dryden Flight Research Center. This project aims to evaluate the effects of sonic booms on EQW sensors. The study consists of exposing high-sample-rate (1000 sps) triaxial accelerometers to sonic booms with overpressures ranging from 10 to 600 Pa in the free field and the built environment. The accelerometers record the coupling of the sonic boom to the ground and surrounding structures, while microphones record the acoustic wave above ground near the sensor.Sonic booms are broadband signals with more high-frequency content than earthquakes. Even a 1000 sps accelerometer will produce a significantly aliased record. Thus the observed peak ground velocity is strongly dependent on the sampling rate, and increases as the sampling rate is reduced. At 1000 sps we observe ground velocities that exceed those of P-waves from ML 3 earthquakes at local distances, suggesting that sonic booms are not negligible for EQW applications.We present the results of several experiments conducted under SonicBREWS showing the effects of typical-case low amplitude sonic booms and worst-case high amplitude booms. We show the effects of various sensor placements and sensor array geometries. Finally, we suggest possible avenues for discriminating sonic booms from earthquakes for the purposes of EQW.
Session:Seismic Sources and Parameters
Presenter   Sweny, Andrea
Schedule   Wed 2:45 PM / Oral
Room   Ballroom E
Correlations between DYFI Intensity and Instrumental Ground-Motion Parameters based on Recent Earthquakes
SWENY, A., University of Western Ontario, London, ON, Canada, asweny@uwo.ca; ATKINSON, G., University of Western Ontario, London, ON, Canada, Gmatkinson@aol.com
Using a few well-documented earthquakes in Eastern and Western North America, we analyze correlations between felt intensity and several ground motion parameters. Events such as the 2008 Mt. Carmel, 2009 Inglewood, and 2010 Baja earthquakes have extensive intensity data derived from the USGS Did You Feel It? (DYFI) website, which can be matched with instrumental ground motion data from seismic stations within the same zip code. Correlations are computed between DYFI (Modified Mercalli) intensity and peak ground acceleration (PGA), peak ground velocity (PGV), and spectral acceleration (PSA) at 0.3, 1 and 3 seconds. The best-correlated parameters with intensity are PGV, and average PSA (over 0.3, 1, 3 seconds). We perform linear regressions of intensity versus these parameters to determine the effect of magnitude/distance on the relationship between intensity and PGV (or intensity and average PSA). We use Kriging techniques to interpolate the residuals from these regressions spatially, and compare them to intensity data, site condition, and ground motion data. This provides insight into the spatial variations in the strength of correlation amongst parameters. We find that, overall, PGV appears to be best correlated with MMI at most distances from the epicenter. In addition, a clear spatial correlation can be seen between the MMI-ground motion relationships and local site conditions.
Session:Creative Wavefield Recording and Analysis
Presenter   Rademacher, Horst
Schedule   Fri 11:30 AM / Oral
Room   Ballroom E
A New Instrumental Approach to Earthquake Early Warning
WITHERS, L., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, lwithers@guralp.com; MCGOWAN, M., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, mmcgowan@guralp.com; PEARCEY, C., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, cpearcey@guralp.com; GURALP, C. M., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, cguralp@guralp.com; RADEMACHER, H., Guralp Systems Ltd., Aldermaston, Berkshire, United Kingdom, hrademacher@guralp.com
Digital data telemetry has led to vast improvements in the quality and the reliability of seismic networks. However, the growing number of Earthquake Early Warning (EEW) systems places new demands on such networks. In EEW systems time is of the essence and every second counts. Here we present a new approach to data processing, which reduces the time it takes for mission critical EEW parameters to reach an alarm center. Depending on the communications protocol, data generated by a field digitizer are bundled into packets. Once a packet is "full", the digitizer will send it to the acquisition computer in the data center. From there data are transferred to processing computers, where the parameters critical for EEW are computed. Depending on the structure of the packets, the design of the telemetry network, the way data are handled within a data center and the algorithms used, it can take up to tens of seconds between the first detection of an earthquake and the availability of EEW parameters to decision makers. To reduce this time we have developed a new way to calculate the parameters, by making full use of the processing capabilities of the digital signal processors (DSP) within our Guralp DM-24 family of digitizers. As much of their capacity is idle during routine digitization, we have reprogrammed and augmented them to continuously calculate a string of EEW parameters at the remote location. We have also made provisions, that user defined code can be programmed onto the DSP in order to optimize the calculation of EEW parameters. The calculated values are immediately transmitted to the data center via a priority telemetry protocol, without the need for bundling them into large packets. At the data center, these values can be immediately used in displays and also to trigger a preset level of alarms. This concept has already been realized in several EEW systems and we will present data from those applications.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Niemi, Tina
Schedule   Thu AM / Poster
Room   Ballroom B
A New Madrid Field Trip for High School Teachers
NIEMI, T. M., University of Missouri-Kansas Ci, Kansas City, MO, niemit@umkc.edu; ADEGOKE, J., University of Missouri-Kansas Ci, Kansas City, MO, adegokej@umkc.edu; STODDARD, E., University of Missouri-Kansas Ci, Kansas City, MO, stoddarde@umkc.edu; ODOM, A. L., University of Missouri-Kansas Ci, Kansas City, MO, alodom@umkc.edu
A multifaceted teacher professional development course (GEOPATHS) was implemented as a partnership between the Kansas City Missouri School district and UMKC. The approach included learning-cycle lesson plans and activities aligned to the Missouri State grade level expectations in matter & energy and force & motion that focus on the underlying physical concepts of earthquakes, earth structure, and plate tectonics, a field trip to the New Madrid seismic zone, and training on desktop seismographs. To provide our teachers with an authentic experience and introduce them to field-inquiry, the second component of our course was a three-day field trip. We traveled to the New Madrid seismic zone to observe first hand the major geomorphic changes in the landscape caused by the New Madrid earthquakes of 1811-1812. Stops included the town and museum of New Madrid, MO, examination of sand blows and liquefaction features in Blytheville, AR, the fault scarp and a boat trip on the Reelfoot Lake to examine the submerged bald cypress trees. The goal of the field trip was to model field-inquiry using observations of the 1811-1812 earthquakes and to become familiar with mid-continent resources and geology. We also visited the Center for Earthquake Research and Information in Memphis, TN. As geoscientists we know from experience that students learn more on a field trip than numerous hours in the classroom. Our survey data show that the teachers valued the field experience and it translated directly to their ability, knowledge base, and enthusiasm in the classroom. Global earthquakes and the tragedy and disaster that they bring are clearly “teachable moments” in the classroom. Many students in the US mid-continent also see earthquakes as distant events that could not possibly touch their lives. By providing our teachers with the experience of traveling and studying these Missouri earthquakes at the epicenter, we give them the tools and personal stories to bring to the classroom.
Session:The Seismo-Acoustic Wavefield
Presenter   Lees, Jonathan
Schedule   Fri 4:00 PM / Oral
Room   Ballroom C
Modeling Volcano Vent Geometry from Diffracted Infrasonic Waveforms
LEES, J. M., University of North Carolina, Chapel Hill, Chapel Hill, NC, jonathan.lees@unc.edu; KIM, K., University of North Carolina, Chapel Hill, Chapel Hill, NC,
Volcanic infrasound provides valuable information about volcano explosion dynamics, although careful modeling is required to separate path from source effects. We demonstrate here that infrasound emanating from a volcanic vent undergoes significant deformation by diffraction at the vent rim edge. Numerical modeling of waveform diffraction along the rim showed high correlation to observed transient infrasonic signals at Karymsky Volcano, Kamchatka, Russia. The nearly conical edifice and simple vent crater makes Karymsky an excellent case study for comparing infrasound wave theory to observations close to the source. In theory, the pulse shape associated with the diffraction depends only on simple characteristics of the vent geometry such that deformed wavefronts can be used to extract geometric parameters via inversion. We adapted this modeling approach to Karymsky acoustic data recorded in weekly field deployments during 1997-1999 campaigns. Explosions rates were as high as 4-10 per hour during these active periods. More than three hundred events were analyzed for which vent diameters were determined. The exhibited range of derived vent diameters appeared to be physically reasonable. We present here a comparison of inferred vent diameters as Karymsky volcano evolved over time and deformation modified the source orifice. The method may be useful for monitoring vent evolution on volcanoes when visual observations are not available.
Session:Guide to Sustainable Seismographic Networks
Presenter   Withers, Mitchell
Schedule   Fri 9:45 AM / Oral
Room   Ballroom C
ANSS Network Architecture; Sharing Data to Improve Coordinated Regional and National Performance.
WITHERS, M. M., University of Memphis, CERI, Memphis, TN, mwithers@memphis.edu; BENZ, H., National Earthquake Information Center, U.S. Geological Survey, Golden, CO, benz@usgs.gov
A newspaper article from December 2010 (Jones, 2010) described a new communication system for law enforcement for the county where one of us lives (Withers). The process of cross checking records from other cities in the county that once meant spending hours on the phone will soon be done in seconds. One of the Police Chiefs said it means they are making progress as they all share data. The Advanced National Seismic System (ANSS) went through a similar transformation in the late 1990's and early 2000's and the benefits are dramatic. Coordination that used to take hours on the phone can now be done automatically in seconds. In this paper we describe the real-time data sharing in the ANSS and discuss the benefits, performance enhancements, and pitfalls. Performance standards now include metrics for data exchange between networks product post times. The real-time availability of stations beyond the authoritative boundary of a regional network provides operational overlap for backup and improved coverage for border events but also requires robust automation to avoid duplication. Real-time data exchange between the NEIC and regional networks provides a level of 24/7 coverage not previously possible, but also comes with ever increasing expectations for timeliness and accuracy.Jones, Yolanda (2010, December 26). Police network unites cities' info. The Commercial Appeal, http://www.commercialappeal.com/news/2010/dec/26/police-network-unites-cities-info/ .
Session:Earth Structure Observations and Theory
Presenter   Martynov, Vladislav
Schedule   Thu 11:15 AM / Oral
Room   Ballroom E
Long Period Modulation of High Frequency (> 0.3 Hz) Seismic Noise and Anisotropy Implications for the San Jacinto Fault Region in Southern California
MARTYNOV, V., IGPP/SIO, UCSD, La Jolla, CA, vladik@epicenter.ucsd.edu; ASTIZ, L., IGPP/SIO, UCSD, La Jolla, CA, lustiz@ucsd.edu; VERNON, F., IGPP/SIO, UCSD, La Jolla, CA, flvernon@ucsd.edu
We observe cyclic variations in the high frequency seismic noise (HFSN) spectra in the range from 0.3 to 7.2 Hz from analysis of about 100 days of three-components broadband data recorded at 10 ANZA seismic stations in Southern California. We explore the HFSN variation as linked to the effect of the periodically changing forces such as Earth tide, atmospheric loading.The continuous data were band-passed through 17 individual octave filters, their RMS amplitudes were stacked and averaged within the Ts – length window. The final result from each station was fitted using the following equation A (f) sin ( + 6.2832 t / Ts). From this analysis, we found a long-period modulation of HFSN with modes S1 -24 hr, S2 -12 hr, S3 -8 hr, S4 -6 hr and M2 -12.42 hr. The seismic noise variation at 24 hours is associated with cultural activity in the region because there is a ‘quiet’ time shift corresponding to the local day-time-savings change. The modulation of HFSN at periods of 12, 8 and 6 hours is correlated with atmospheric pressure variation measurements at the Pinion Flats Observatory. We also find that at frequencies from 0.3 to 0.6 Hz there is HFSN variation corresponding to the M2 Earth tide mode.To explore if the amplitude of the modulation may be directional, we use data from station SND, located on the San Jacinto fault zone. We calculate the long-period variation of HFSN for the modes S2 and M2 as a function of direction of seismic noise polarization at 0.3 and 0.6 Hz. We find that the smallest amplitudes variation has a strike 315° and dip 88° for the mode S2 at frequency 0.3 Hz, corresponding to the azimuth and dip of the San Jacinto fault zone. Analysis of data from other ANZA stations are in agreement with this result with the exception of stations FRD and BZN, reflecting the preferred orientation of sub-faults parallel to the main faulting of the San Jacinto fault zone.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Ayele, Mehari
Schedule   Wed AM / Poster
Room   Ballroom B
Effect of Empirical Seismic Instrument Corrections on Gradiometry Parameter Estimates
AYELE, M. M., Center of Earthquake Research and Information, U O Memphis, Memphis, TN, mmayele@memphis.edu; LANGSTON, C. A., Center of Earthquake Research and Information, U O Memphis, Memphis, TN, clangstn@memphis.edu
Empirical seismic instrument corrections provided by the IRIS Waveform Quality Control Center have been used to evaluate the effect of the corrections on the accuracy of wave gradiometry parameter estimates. We applied the scaling factor and the wave arrival angle anomaly on instrument response-corrected and filtered (0.008 - 0.01 Hz) US Transportable Array (TA) data. Vertical and radial component data recorded from April, 4, 2007, magnitude 7.6 Solomon earthquake were processed for a 9 element subarray of the TA. The amplitude corrections were applied to the vertical component and the arrival angle anomaly to the computation of the radial component. Errors in the wave parameters determined from wave gradiometry were evaluated using a Monte Carlo technique. Vertical component gradiometry results show that the error ranges from -3.8 to 4.2 degree for the wave azimuth, -0.05 s/km to 0.09 s/km for the wave slowness; -0.0007 to 0.0014 per km and -0.0013 to -0.0031 per degree for wave spreading and wave radiation respectively. Similarly radial component gradiometry error ranges were -0.61 to 1.37 degree; -0.026 s/km to -0.0114 s/km; -0.00115 to 0.00208 per km and -0.0003 to 0 .0001 per degree respectively for the wave attributes. Applying these empirical correction factors for the wave gradiometry technique usually are insignificant except for wave slowness determined from the vertical component. It would be prudent to evaluate gradiometry results by applying the empirical correction factors in high resolution studies.
Session:Seismic Sources and Parameters
Presenter   Shao, Guangfu
Schedule   Wed 4:45 PM / Oral
Room   Ballroom E
Slip History of the 2010 Mw 7.0 Darfield, New Zealand Earthquake Constrained by Inverting Strong Motion and Teleseismic Observations
SHAO, G., University of California, Santa Barbara, CA, shao@umail.ucsb.edu; JI, C., University of California, Santa Barbara, CA, ji@geol.ucsb.edu
We study the rupture process of the 2010 Mw 7.0 Darfield, New Zealand earthquake by modeling both teleseismic waveforms and near-field strong motion data recorded by the GeoNet. We derive the fault geometry from the geological surface observations and calculate the earth response using a 1D velocity model interpolated from local tomographic studies. Our preferred model shows the rupture initiates at a depth of 9 km on a vertical fault plane and then propagates bilaterally for about 35 km along the strike with an average rupture velocity as slow as 0.8 km/s. The Darfield earthquake is dominant by strike-slip motion and the majority moment release occurs in the east of the hypocenter at depths less than 10 km with a peak slip larger than 9 m. The total duration of the Darfield earthquake is 34 s with negligible moment in the beginning 10 s and more than 80% of the total seismic moment between 10 and 22s. The total seismic moment of the Darfield earthquake is 5.2 x 1019 Nm. We will further combine near-field geodetic observations into this investigation.
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Modrak, Ryan
Schedule   Thu 8:45 AM / Oral
Room   Ballroom E
Rift structure of East Africa from joint inversion of group velocity estimates and gravity data
MODRAK, R. T., Princeton University Department of Geosciences, Princeton, NJ, rmodrak@princeton.edu; MACEIRA, M., Los Alamos National Laboratory Earth and Environmental Sciences Division, Los Alamos, NM, ; VAN WIJK, J. W., University of Houston Department of Earth and Atmospheric Sciences, Houston, TX, ; PASYANOS, M. E., Lawrence Livermore National Laboratory Department of Earth and Atmospheric Sciences, Livermore, CA,
We invert for shear velocity structure of East Africa by adapting previous joint inversion methods to the region’s unique tectonic setting. To increase the usefulness of gravity data, this approach entails high-pass gravity filtering. While group velocity measurements tend to average structure over large horizontal and vertical distances, filtered gravity anomalies are expected to possess highest resolving power at shallow depths and short wavelengths and thus enhance resolution of crustal and uppermost mantle structure. Results from the joint inversion demonstrate a simultaneous fit to both data sets. Beneath Tanzania we resolve high velocities above 120 km depth and low velocities below 140 km depth, consistent with a hot plume overlain by cool, cratonic lithosphere. Beneath Ethiopia we resolve a shallower low-velocity anomaly, suggesting extensive lithospheric thinning accompanying Ethiopia’s late-stage rifting. We find no evidence that the low-velocity anomalies beneath Ethiopia and Tanzania merge continuously above 175 km depth.
Session:Microzonation and Urban Seismic Hazard Mapping: Current Efforts and Future Directions
Presenter   Jaume, Steven
Schedule   Thu 10:45 AM / Oral
Room   Room 204/205
Seismic Site Amplification in Charleston, South Carolina: Modeling and Interpretation
JAUME, S. C., Department of Geology, College of Charleston, Charleston, SC, jaumes@cofc.edu; MINER, K. S., Department of Biology, College of Charleston, Charleston, SC, ksminer@edisto.cofc.edu
We calculated a series of synthetic seismograms using a wavenumber integration technique to model the linear seismic response of geological structure in the Charleston, South Carolina region. These seismograms were produced using a combination of vertical and horizontal surface sources and geotechnical borehole derived velocity structures. Horizontal-to-vertical spectral ratios (HVSR) of the synthetic seismograms match the observed 0.2 Hz and 1-2 Hz spectral peaks in the microtremor HVSR study of Miner and Jaume (this volume) and correspond to resonances produced in the entire ~1000 meter sedimentary section and from the upper 50-60 meters of the section respectively. However, our models, which assume linear behavior of the entire sedimentary section, also produce higher frequency resonances as predicted by Chapman et al. (2008), but which are not seen in the observed HVSR’s. This suggests that the Quaternary section in Charleston is behaving non-linearly, even at very low strains. We also investigated the apparent amplification of the 1-2 Hz resonance peak at sites on artificial fill. In many cases artificial fill overlies Holocene tidal marsh deposits with Vs as low as 50 m/sec. Modeled HVSR’s of these “fill over marsh” sites show increased amplification of the 1-2 Hz peak when compared to models where the fill material is removed. This is also consistent with observations from an ANSS strong motion vault located at a “fill over marsh” site; i.e., the 1-2 Hz resonance peak is suppressed in ground motion taken inside the vault (which has foundations that extend into marsh deposits) versus ground motion at the surface. This suggests the relative amplitude of the 1-2 Hz resonance may be an effective exploration tool for determining the extent of “fill over marsh” areas on the edges of the Charleston peninsula.
Session:Geotechnical Lessons Learned from Recent Earthquakes: Haiti, Chile, Baja CA, New Zealand
Presenter   Green, Russell
Schedule   Fri 8:45 AM / Oral
Room   Room 204/205
Geotechnical Aspects of the Mw7.1, 4 September 2010, Darfield, New Zealand, Earthquake
GREEN, R. A., Virginia Tech, Blacksburg, VA, rugreen@vt.edu; CUBRINOVSKI, M., University of Canterbury, Christchruch, New Zealand, misko.cubrinovski@canterbury.ac.nz; ASHFORD, S. A., Oregon State University, Corvallis, OR, scott.ashford@oregonstate.edu; HUTCHINSON, T., University California at San Diego, La Jolla, CA, tahutchinson@ucsd.edu; KAVAZANJIAN, E., Arizona State University, Tempe, AZ, edkavy@asu.edu; BRADLEY, B., University of Canterbury, Christchurch, New Zealand, brendon.bradley@canterbury.ac.nz; COX, B., University of Arkansas, Fayetteville, AR, brcox@uark.edu; ORENSE, R., University of Auckland, Auckland, New Zealand, r.orense@auckland.ac.nz; PENDER, M., University of Auckland, Auckland, New Zealand, m.pender@auckland.ac.nz; ALLEN, J., TRI/Environmental, Inc., Austin, TX; Quigley, M., University of Canterbury, Christchurch, New Zealand; WOTHERSPOON, L., University of Auckland, Auckland, New Zealand, l.wotherspoon@auckland.ac.nz; O'ROURKE, T.,Cornell University, Ithaca, NY, tdo1@cornell.edu; ALGIE, T., University of Auckland, Auckland, New Zealand
On 4 September 2010, a Mw7.1 earthquake struck the Canterbury region of New Zealand. The epicenter was located near Darfield, about 40 km west of the Central Business District of Christchurch. This was the most damaging earthquake to occur in New Zealand since 1931. Liquefaction and lateral spreading were pervasive in portions of Christchurch and neighboring communities, causing extensive damage to buried utilities (water and wastewater pipelines), residential housing, and other building structures. Despite the severe damage to infrastructure and residential houses, no deaths occurred and only two injuries were reported in this earthquake. From an engineering viewpoint, the most significant aspects of the 2010 Darfield Earthquake were primarily geotechnical in nature. The Christchurch and Waimakariri Districts, and to a lesser extent the Selwyn District, all had damage to pipeline networks that resulted in the loss of service and discharge of untreated wastewater into the groundwater and surface water. In all three districts, drinking water is untreated well water. Liquefied sand and water entered sewer lines though breaks and separations in the pipe, and cleaning the sand from wastewater conduits and pump stations slowed service restoration. However, by far, one of the greatest impacts of this earthquake on the residents in the Canterbury region was the lateral spreading and post-earthquake differential settlement that damaged numerous residential and other structures. An estimated 4000 houses were damaged beyond repair, predominately due to these mechanisms. Particularly hard hit were the Christchurch neighborhoods of Dallington, Avonside, and Bexley, outlying neighborhood of Halswell (southwest of Christchurch), outlying neighborhoods of Spencerville and Brooklands (northeast of Christchurch), and Kaiapoi and Pines Beach (northeast of Christchurch, north of the Waimakariri River). Flood protection levees in the region also experienced some damage.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Peng, Zhigang
Schedule   Thu PM / Poster
Room   Ballroom B
Tremor and Creep Events on the Deep San Andreas Fault Triggered by Local, Regional, and Teleseismic Earthquakes
PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng@gatech.edu; SHELLY, D. R., United States Geological Survey, Menlo Park, CA, dshelly@usgs.gov; HILL, D. P., United States Geological Survey, Menlo Park, CA, hill@usgs.gov; AIKEN, C., Georgia Institute of Technology, Atlanta, GA, chastity.aiken@gmail.com
The potential of earthquakes to trigger distant fault slip is well established, yet the significance of remote triggering and its role in tectonic deformation remains controversial, in part because triggering is often delayed. Tectonic tremor activity, which appears to reflect deep fault slip, is exceedingly sensitive to small stresses, including tidal stresses and passing seismic waves from both teleseismic and regional earthquakes. Here, we study tremor activity along the central San Andreas Fault (SAF) from mid-2001 to early 2010, scrutinizing its relationship with local, regional and teleseismic earthquakes. Based on similarities in the shape and timing of seismic waveforms, we conclude that triggered tremor shares common sources and a common physical mechanism with ambient tremor that initiates in the absence of incoming seismic waves. Utilizing this similarity in waveforms, we detect tremor triggered by numerous teleseismic, regional and local events, including previously unreported triggering from the relatively small 2007 Alum Rock and 2008 Chino Hills moment magnitude (Mw) 5.4 regional earthquakes, and several Mw>3.0 earthquakes at local to regional distances. We also find multiple examples of systematic migration in triggered tremor, similar to tremor migration episodes observed at other times. Because these episodes propagate much more slowly than the triggering waves, the migration likely reflects a small, triggered creep event. As with ambient tremor bursts, triggered tremor at times persists for multiple days, probably indicating a somewhat larger, but still small, creep event. This activity provides a clear example of delayed dynamic triggering, with a mechanism perhaps also relevant for triggering of regular earthquakes.
Session:Guide to Sustainable Seismographic Networks
Presenter   Kilb, Debi
Schedule   Fri PM / Poster
Room   Ballroom B
Ocean Observatories Initiative’s Cyberinfrastructure (OOI-CI): Providing a Link Between Research and Discovery
KILB, D., Scripps Inst. of Oceanography, La Jolla, CA, dkilb@ucsd.edu; KEEN, C. S., Scripps Inst. of Oceanography, La Jolla, CA, cskeen@ucsd.edu; PEACH, C., Scripps Inst. of Oceanography, La Jolla, CA, cpeach@mail.ucsd.edu; ORCUTT, J., Scripps Inst. of Oceanography, La Jolla, CA, jorcutt@ucsd.edu; VERNON, F. L., Scripps Inst. of Oceanography, La Jolla, CA, flvernon@ucsd.edu
Emerging trends indicate the traditional approach of individuals, or small groups of scientists, working to solve problems within a single science domain is being superseded by demands for multidisciplinary and interdisciplinary research. Coupled with exponential growth in information technology these trends are irrevocably changing how science is done. We are now moving beyond relational databases and traditional object oriented programming that require changes be made by one person at a time. Instead, systems are being built that allow multiple processes to act concurrently even within the same data stream. These types of techniques are being implemented by the cyberinfrastructure component of the Ocean Observatories Initiative (OOI-CI), which is building a national virtual observatory to provide scientists tools to interactively collaborate and analyze data, data processes and experiment designs. Data for this project will be collected by OOI service nodes (Regional Scale Nodes, Coastal Arrays, and Global Scale Buoys) connected via a high speed network extending from the ocean floor to Cyberinfrastructure Points-of-Presence (CyberPOPs). A principal objective is to move beyond the typical model of a central data management system, instead providing an infrastructure of services for the user, including compute and storage cloud resources (i.e., to use it you do not need software or a server). Scheduled seismic deployments included broadband seafloor data recordings and short period seismic arrays to measure ground velocity near sites of methane seeps and regions of hydrothermal upflow. The information exchange model can be thought of as ‘Google backwards’, where the data searches for you instead of you searching for the data. This program will also offer tools to interactively analyze and visualize data within a social networking environment. We will be acting as liaisons between the OOI-CI and education and public engagement projects and we welcome new partners.
Session:Guide to Sustainable Seismographic Networks
Presenter   Vernon, Frank
Schedule   Fri 9:15 AM / Oral
Room   Ballroom C
Lessons Learned Through the Design and Implementation of Portable, Transportable, and Permanent Seismic Systems
VERNON, F. L., UCSD, La Jolla, CA, flvernon@ucsd.edu
There is a design of the USArray Transportable Array was based on experiences learned through the design, development, and deployment of IRIS sponsored Kyrgyz Broadband Seismic Network (KN) along with the IRIS PASSCAL Broadband Telemetry Array beginning in the early 1990s. The USArray Transportable Array was initially designed to deploy a 400 element array with nominal 70 km station spacing starting on the west coast of the continental US, followed by a rolling deployment by removing stations on the west side of the array and redeploying these instruments on the eastern margin with each station emplaced for approximately 2 years. Since the original station design of the TA, the capabilities have been significantly improved by upgrading the dataloggers, adding meteorological sensors, additional station SOH channels, and replacing the original onsite storage with a second generation. The most recent TA design change is the current rollout of additional sensors to measure infrasound signals. The foundation of the TA was based on the combination of state-of-the-art sensors, dataloggers, IP communication systems, data acquisition software, servers, and storage. In 2004, we started building the hardware and software architecture to receive streaming realtime seismic and SOH channel data from this dynamic array. Over time we have developed a series of flexible development protocols to solve several classes of problems associated with the day-to-day running of such a complex network while still providing high data return rates. One class of difficult problems faced in the USArray project is related to the dynamic nature of the moving array. A second class of problems are based on the scaling of the data, processing, and storage requirements.We will discuss our approaches to solving problems in this dynamic environment and provide our views of how the next generations of systems can be designed to mitigate these types of problems.
Session:Guide to Sustainable Seismographic Networks
Presenter   Ingle, Stephanie
Schedule   Fri 10:45 AM / Oral
Room   Ballroom C
Lessons Learned from Five Years of Sustained Cabled Ocean Observing System Operation
INGLE, S., Lighthouse R & D Enterprises, Inc., Houston, TX, single@lighthousehouston.com; DU VALL, K., Lighthouse R & D Enterprises, Inc., Houston, TX, kduvall@lighthousehouston.com; SNIDER, J., Lighthouse R & D Enterprises, Inc., Houston, TX, jsnider@lighthousehouston.com; JUNTUNEN, K., Lighthouse R & D Enterprises, Inc., Houston, TX, kjuntunen@lighthousehouston.com
Lighthouse R & D Enterprises, Inc. has operated a cabled marine observatory off the coast of Oman since 2005. In 2007, the observatory was expanded to include a seismic tsunami early warning system (STEWS). In early 2010, an additional cabled ocean observatory was deployed in 3000 meters of water. Installation and operation of a highly reliable, real-time, fiber-optic system in a dynamic marine environment presented several challenges. We will highlight our mitigation methods and lessons learned including: (1) the importance of location selection, particularly in the case of the STEWS (or any seismic network); (2) production and delivery of real-time, time-series data to the host country or international community over an extended period of time requires regularly scheduled maintenance; (3) training of host country technicians and scientists to maintain the system and process, interpret and utilize the data to eventually take on full responsibility; (4) delivery of data in a format that is both acceptable to the host country and that meets international standards.The benefits of tsunami warning systems or seismic networks clearly transcend political boundaries to multiple countries or even entire regions of the world. However, costs are typically borne out by a single host country (and often a single ministry within that country) or from their portion of funds from an international agency. To improve the chances of installation funding, there must be additional pressure on international agencies to provide support for regional networks. An increase in scientific collaboration and information sharing across borders will also facilitate network- and cost-sharing agreements. In addition to the initial investment, long-term investment in the education of host-country technicians and scientists must be recognized by stakeholders as a critical factor in the ultimate success of the network or system.
Session:Geotechnical Lessons Learned from Recent Earthquakes: Haiti, Chile, Baja CA, New Zealand
Presenter   Seale, Sandra
Schedule   Fri PM / Poster
Room   Ballroom B
Wavelet Analysis of Pore Pressure Data Recorded from the 2010 El Mayor - Cucapah Earthquake at the NEES@UCSB Wildlife Site
SEALE, S. W. H., Earth Research Institute, UCSB, Santa Barbara, CA, sandy@eri.ucsb.edu; LAVALLEE, D., Earth Research Institute, UCSB, Santa Barbara, CA, daniel@eri.ucsb.edu; STEIDL, J. H., Earth Research Institute, UCSB, Santa Barbara, CA, steidl@eri.ucsb.edu; RATZESBERGER, L. H., Earth Research Institute, UCSB, Santa Barbara, CA, hankr@eri.ucsb.edu; HEGARTY, P., Earth Research Institute, UCSB, Santa Barbara, CA, hegarty@eri.ucsb.edu
On 4 April 2010, the M7.2 Sierra el Mayor – Cucapah event occurred in Baja California, Mexico. The NEES@UCSB Wildlife Liquefaction Array (WLA) in the Imperial Basin is located 110 km NNW of the epicenter. The event was recorded on all channels: by three-component strong-motion accelerometers at the surface and in boreholes at various depths and by pore pressure transducers located in a saturated, liquefiable layer. We have computed the spectra of the pore pressure response in the frequency domain for signals recorded at different depths. At each depth, the spectrum is attenuated as a power law with a sharp discontinuity at a frequency close to 0.16 Hz. Partially due to the late arrival of the surface waves, the frequency content of the recorded pore pressure signal is a function of time. To gain a better understanding of the time-dependence of the frequency content, we performed wavelet transforms of the full signals. Analysis of the wavelet transforms demonstrates that the dominant energy in the recorded signal shifts over time from low frequencies to higher frequencies.Using wavelet transforms, we computed the acceleration amplitudes at different scales (or frequencies). We then computed the correlations between the pore pressure signals at various scales and the corresponding acceleration records. The results show that at relatively high frequencies, the pore pressure correlates well with the vertical accelerations while at lower frequencies, the pore pressure correlates well with the horizontal accelerations. For the duration of the signal, we compared the amplitudes of the pore pressure to the amplitudes of the ground motion at different scales. Compared to the ground motion, the results suggest an important contribution of the large scale (or low frequency) amplitudes to the pore pressure signal. This result may have important consequences for assessing the liquefaction hazard potential of saturated soils.
Session:Improving Inventory and Vulnerability Data for Earthquake Loss Modeling
Presenter   Marano, Kristin
Schedule   Fri AM / Poster
Room   Ballroom B
USGS PAGER Global Earthquake Alerts Based on Rapid Estimates of Economic Loss and Casualty Information
MARANO, K. D., US Geological Survey, Golden, CO, kmarano@usgs.gov; WALD, D. J., US Geological Survey, Golden, CO, wald@usgs.gov; JAISWAL, K., US Geological Survey, Golden, CO, kjaiswal@usgs.gov; HEARNE, M., US Geological Survey, Golden, CO, mhearne@usgs.gov; BAUSCH, D., FEMA, Denver, CO, douglas.bausch@dhs.gov
Estimated economic loss and casualty information are now included in earthquake alerts sent out by the U.S. Geological Survey (USGS) following significant earthquakes around the world. These earthquake alerts are widely recognized and used by emergency responders, government and aid officials, and the public to understand the scope of the potential disaster and to develop the best response. The USGS automated system, PAGER (Prompt Assessment of Global Earthquakes for Response), rapidly assesses earthquake impacts by estimating the shaking distribution, the number of people and settlements exposed to severe shaking, and the range of possible fatalities and economic losses. The estimated losses trigger the appropriate color-coded alert, which suggest levels of response: no response needed (green); local or regional (yellow), national (orange) or international (red). The certainty of such alerts depend greatly on the input, including the earthquake parameters (epicenter, depth, magnitude), the hazard calculated via ShakeMap (based on the automatically selected Ground Motion Prediction Equation, or GMPE), the estimated population exposure, and the country-specific empirical loss models. These components interact to set the alert levels, whose validity tends to improve over time as the details of the earthquake parameters and shaking hazard become better known. This refinement process can take anywhere from minutes to hours depending on the earthquake, yet the initial alert levels still provide early, valuable information to responders and the public. We will show the usefulness of PAGER alerts while critiquing current limitations, uncertainties, and how our estimates and loss-based alerts have performed over the past year (since their inception).
Session:Seismic Sources and Parameters
Presenter   Cantavella, Juan
Schedule   Wed AM / Poster
Room   Ballroom B
Evaluating a Procedure to Estimate a Summary Earthquake Moment-Magnitude (Mw) from Magnitudes Computed by Different Procedures
CANTAVELLA, J. V., Instituto Geográfico Nacional, Madrid, Spain, jvcantavella@fomento.es; BULAND, R. P., U.S. Geological Survey, Denver, CO, rbjoland@gmail.com; DEWEY, J. W., U.S. Geological Survey, Denver, CO, jdewey@usgs.gov; EARLE, P. S., U.S. Geological Survey, Denver, CO, pearle@usgs.gov; PRESGRAVE, B. W., U.S. Geological Survey, Denver, CO, presgrave@usgs.gov
Following the occurrence of an earthquake, rapid estimates of earthquake magnitude are typically based on automatic processing of preliminary data. A few, rapidly calculated, magnitude types will be available soon after the shock, followed by magnitude types that depend on progressively later arriving phases or more elaborate computation procedures. An estimate of the early value of a given magnitude-type is calculated even as new data are about to arrive that might cause the value of that type of magnitude to change. From the standpoint of informing the public and notifying emergency-response authorities, it is desirable that early magnitude estimates be accurate and stable approximations of the moment-magnitudes (Mw) that will ultimately result from human-reviewed moment-tensor inversions. In 2008, the USGS National Earthquake Information Center (NEIC) began testing a procedure, developed by R. P. Buland, to calculate an estimate of Mw that is a linear combination of other magnitude types, including both traditional magnitudes based on maximum amplitudes of single phases and magnitudes derived from moment-tensor inversions. The new magnitude, denoted Summary Magnitude, takes advantage of the increasing number of magnitude types being calculated at the NEIC. For most earthquakes, the Summary Magnitude is a good approximation of final Mw. Because it is based on many magnitude types, it is commonly more stable with time than an event magnitude that sequentially changes from one magnitude type to another as magnitude types of progressively higher preference become available. In the present study, we evaluate the performance of the Summary Magnitude on earthquakes of 2010, a data set that is independent of the data set used to calibrate the Summary Magnitude procedure.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Baise, Laurie
Schedule   Thu 4:15 PM / Oral
Room   Ballroom E
A Variance-Weighted Approach to Site Response Mapping
THOMPSON, E. M., Tufts University, Medford, MA, eric.thompson@tufts.edu; BAISE, L. G., Tufts University, Medford, MA, laurie.baise@tufts.edu; KAYEN, R. E., United States Geologic Survey, Menlo Park, CA, rkayen@usgs.gov; MORGAN, E. C., Tufts University, Medford, MA, eugene.morgan@tufts.edu; KAKLAMANOS, J., Tufts University, Medford, MA, james.kaklamanos@tufts.edu
The scale of previously proposed methods for mapping site response ranges from global coverage down to individual urban regions. Typically, spatial coverage and accuracy are inversely related. We use the densely spaced recorded strong motions in Parkfield, California, to estimate the accuracy of different site response mapping methods and demonstrate a method for integrating multiple site response estimates. Individual site response estimates are derived both from local and regionally available data. The local site response models include those based on velocity profiles using both Vs30 (30 m divided by the S wave travel time to 30 m depth) and the square-root-of-impedence method and predominant site period estimated from recorded ground motions. The regional site response models include topographic slope and surficial geology based site response correlations. The proposed variance-weighted approach to site response mapping is the weighted mean of the suite of these different estimates, where the weights are the inverse of the variance of the individual estimates. Thus, the dominant site response model varies in space as a function of the accuracy of the individual models. For mapping applications, site response models should be judged in terms of both spatial coverage and the degree of correlation with observed amplifications. Performance varies with period, but in general the Parkfield data show that:(1) where a velocity profile is available, the square-root-of-impedance method outperforms the measured Vs30, and(2) where velocity profiles are unavailable, the topographic slope method outperforms surficial geology for short periods, but geology outperforms slope at longer periods.
Session:Combining Geodetic and Seismic Measurements
Presenter   Davis, James
Schedule   Fri PM / Poster
Room   Ballroom B
Noise reduction in High-Rate GPS Seismograms by Array Phase Match Filtering
DAVIS, J. P. D., The University of Memphis, Memphis, TN, jpdavis@memphis.edu; SMALLEY, R., The University of Memphis, Memphis, TN, rsmalley@memphis.edu
Satellite signal multipath is the largest source of noise in high-rate GPS seismograms. We develop and examine the usefulness of array phase match filtering to reduce multipath and uncorrelated noise on synthetic high-rate GPS seismograms of increasing noise amplitude. We then apply array phase match filtering to real high-rate GPS seismograms from the Mw=9.0 December 26, 2004, Sumatra, and Mw=8.8 February 27, 2010, Chile earthquakes.
Session:Regional Seismic Hazard Evaluation: Updates, Policy, and the Public
Presenter   Anderson, John
Schedule   Thu 4:30 PM / Oral
Room   Ballroom E
Results of the Workshop on Applications of Precarious Rocks and Related Fragile Geological Features to US National Hazard Maps
ANDERSON, J. G., Nevada Seismological Laboratory, Reno, NV, jga@unr.edu; BRUNE, J. N., Nevada Seismological Laboratory, Reno, NV, brune@seismo.unr.edu; BIASI, G., Nevada Seismological Laboratory, Reno, NV, glenn@unr.edu; PURVANCE, M., Itasca Consulting Group and Nevada Seismological Laboratory, Reno, NV, mdp@seismo.unr.edu; ANOOSHEHPOOR, A., U. S. Nuclear Regulatory Commission, Washington, DC, Rasool.Anooshehpoor@nrc.gov
The Workshop on the Applications of Precarious Rocks and Related Fragile Geological Features to US National Hazard Maps met at the University of Nevada Reno on October 4-5, 2010. The goal was to develop recommendations to the USGS on the use of precariously balanced rocks (PBRs) and other fragile geological features (FGFs) to improve the national seismic hazard maps. The context is the recognition that hazard curves, and the derived hazard maps, are the calculated output of hazard models that should be tested, and that FGFs currently provide the only data to validate the calculated hazard curves at low probabilities (~10-4 or less).There was a rough consensus that FGFs can help improve the national hazard model in a few general ways. Locally, PBRs may require changes to models of seismicity, where geologically a fault may be considered active, but the PBR suggests not. Within a hazard assessment they can identify inconsistent branches in the logic tree. FGFs that have survived recent earthquakes can test ground motion prediction equations (GMPEs) or synthetic seismograms proposed as models for that event. FGF survival also highlights the distinction between site-specific hazard curves, with which FGFs must be consistent, and hazard curves developed for the national hazard maps using a generic site condition. The GMPEs used for the national maps include the full variability of site response for sites with VS30=760 m/s, while the variability (single-station sigma) at FGFs can be smaller and sometimes measured. Since hazard estimates at small probabilities are sensitive to sigma, some inconsistency of FGFs and national hazard maps may be the cost of the lack of knowledge of specific site response. The workshop also suggested research needed to increase the usefulness of FGFs in the future, and guidelines for archiving the data. A report on the workshop has been submitted to Seismological Research Letters.
Session:Episodic and Complex Behavior of Faulting and Seismicity in Continental Intraplate Regions - Implications for Seismic Hazard Maps
Presenter   Lamontagne, Maurice
Schedule   Thu 2:00 PM / Oral
Room   Ballroom C
Similarities and Differences among the Seismic Areas of the St. Lawrence Paleorift
LAMONTAGNE, M., Natural Resources Canada, Ottawa, ON, Canada, malamont@nrcan.gc.ca; RANALLI, G., Carleton University, Department of Earth Sciences, Ottawa, ON, Canada, granalli@earthsci.carleton.ca
It has been proposed that the St. Lawrence Paleorift System, a series of regional-scale normal faults, is the main geological structure responsible for most of the earthquake activity of the St. Lawrence valley. Most regional normal faults correspond to lineaments or geophysical trends generally parallel to the St. Lawrence River. Field mapping, remote sensing, magnetic, gravimetric and seismic reflection data define the positions of these geological faults. The earthquakes, on the other hand, do not occur along the full length of the system. They concentrate in three seismic zones: Lower St.Lawrence, Charlevoix and Western Quebec, separated by nearly aseismic regions. We examine the seismotectonic similarities and the differences that exist between areas of enhanced earthquake activity, such as the CSZ, and compare them with areas where normal faults exist but where very few earthquakes occur.One of these three areas, the Charlevoix Seismic Zone (CSZ), is the most active seismic zone of eastern Canada with 5 historical earthquakes in the magnitude 6 to 7 range and continuous micro-earthquake activity. Approximately 250 earthquakes with ML larger than 0.0 are recorded yearly by the local seismograph network. Due to this network, the earthquake activity is the best studied of the three areas. In the CSZ, most regional faults bound active volumes while one correlates with earthquake hypocentres, including some magnitude > 4 events. Inside the impact crater, earthquakes are generally of smaller magnitude, possibly due to the high fracturing associated with the Charlevoix impact structure. Most microearthquakes appear to occur in highly fractured volumes, partly related to the impact structure. No surface rupture is found on the seismic reflection lines acquired on the St. Lawrence River. Due to the special characteristics of the CSZ and of its earthquake activity, it is also possible that the CSZ differs from the rest of the St. Lawrence paleorift system.
Session:Guide to Sustainable Seismographic Networks
Presenter   Willemann, Raymond
Schedule   Fri 11:15 AM / Oral
Room   Ballroom C
Outline for a Guide to Sustainable Earthquake Monitoring Systems
WILLEMANN, R. J., IRIS Consortium, Washington, DC, ray@iris.edu; LERNER-LAM, A., Lamont-Doherty Earth Observatory, Palisades, NY, lerner@ldeo.columbia.edu; SANDVOL, E., University of Missouri, Columbia, MO, sandvole@missouri.edu
The audience for a network guide extends to government officials, aid agencies, and developmentbanks, with expertise outside of science & technology. Thus, one objective is to communicateknowledge about earthquake monitoring systems sufficient to create an organization with thepersonnel, finances, and infrastructure necessary to operate the complete system sustainably andto deliver useful products promptly & reliably. We offer an outline for a guide to address thatobjective concisely and without technical language.Purpose of a system: produce a catalog of earthquake locations & sizes; disseminaterapid notifications; promptly estimate loss (with additional expertise; societal information);accrue a catalog for progressively more precise hazard analyses.Components of a system: seismographs make continuous records of ground motion; acommunications infrastructure telemeters data; automatic processing and expert analysis; long-termmanagement of data and products.Analysis specifics: the need for data quality control; detection thresholds thatdepend on network configuration; the limited accuracy of location & magnitude; the expertiserequired for more sophisticated products; product timelines.Station installation and servicing: different types of seismometers, data loggers,and telemetry; the need for qualified, well-equipped field engineers.Build a center: to process, analyze, archive and mange data, with descriptions of thecomputers, data storage, software, and staff that are required.Use the results: alert the government; inform the public; perform seismic hazardanalysis and microzonation studies; support engineers and city planners developing building codes.Ongoing activities and investments: operating costs; periodically replacinginstruments, computers & software; training staff; evaluating system performance; the role ofuniversity researchers.
Session:Creative Wavefield Recording and Analysis
Presenter   Dencker, Tammy
Schedule   Fri PM / Poster
Room   Ballroom B
Three dimensional wave gradiometry
DENCKER, T., Augusta State University, Augusta, GA, tdencker@bellsouth.net; POPPELIERS, C., Augusta State University, Augusta, GA,
Wave gradiometry uses spatial gradients of the displacement wavefield to determine vector slowness, geometrical spreading, and radiation pattern. A gradiometer is an array that is optimized to perform wave gradiometry, and typically has an aperture of less than 10% of the wavefield’s central wavelength. This is in contrast to a traditional phased array which can have an aperture of ten to one hundred times the wavefield’s central wavelength. There have been significant developments in one- and two-dimensional wave gradiometry using seismic arrays. In this work, we extend gradiometry into three dimensions using acoustic sensors. We constructed a three dimensional lattice and attached off-the-shelf microphones at specific points on the lattice structure. Using the National Instruments Labview hardware and software, the acoustic sensors become a phased, three dimensional array. As proof-of-concept, we recorded a broadband acoustic source and then analyze the resulting data using a three-dimensional implementation of wave gradiometry.
Session:Verification Science
Presenter   Fujita, Kazuya
Schedule   Fri AM / Poster
Room   Ballroom B
Revised Source Parameters for PNEs in the Sakha Republic (Yakutia), Russia
FUJITA, K., Dept. of Geological Sciences, Michigan State University, East Lansing, MI, fujita@msu.edu; MACKEY, K. G., Dept. of Geological Sciences, Michigan State University, East Lansing, MI, mackeyke@msu.edu; HARTSE, H. E., Los Alamos National Laboratory, Los Alamos, NM, hartse@lanl.gov; JIH, R. S., Department of State / AVC Bureau, Washington, DC, jihrs@state.gov
Although ground truth locations for peaceful nuclear explosions (PNEs) conducted in the former Soviet Union are generally thought to be known, information (maps, photographs, descriptions) published in radionuclide contamination and environmental studies, combined with satellite imagery, allow for the improvement of the coordinates of many of these detonations to the GT-0 to GT-1 level. Such data include better descriptions and maps of locations, as well as photographs and detailed maps of contaminated areas. We are able to link disturbed areas in satellite imagery to probable detonation sites for all the PNEs in the Sakha Republic (Yakutia) and improve on, or reconfirm, previously published solutions; taking possible uncertainties and alternative sites into consideration, almost all of them can be identified to within 0-2 km. The improvements are most pronounced for Crystal, where a mound over the detonation site can be identified, and the detonations for enhanced petroleum recovery near Tas-Yuryakh (Neva series). These improved locations can be used as the basis for travel-time studies to improve our understanding of crustal velocities and structure in the Siberian platform. Local and regional seismic data are also being analyzed to derive the best seismic-based origin times, which differ from the reported detonation times by a few seconds in several cases.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Bolton Valencius, Conevery
Schedule   Wed 8:30 AM / Oral
Room   Ballroom C
Vernacular Science of the New Madrid Earthquakes: Creating Knowledge in the Early United States
BOLTON VALENCIUS, C., Harvard University, Cambridge, MA, cvalenc@fas.harvard.edu
In the winter of 1811-12, a series of sizable tremors rippled out from the middle Mississippi Valley. What we now term the New Madrid earthquakes were of immediate and pressing concern to the North Americans displaced, shaken, or frightened by them. This presentation, from a forthcoming book on changing historical understandings of the New Madrid Seismic Zone, argues that the intense public interest and discussion surrounding the New Madrid earthquakes reveals a multi-faceted world of vernacular science in the early United States. During the long sequence of earthquakes and in the months, years, and decades after, observers took weather measurements; recorded the effects of the shocks on their homes, livestock, and their own bodies; created devices for revealing the intensity and direction of the shocks; and investigated a multitude of effects from fouled wells to strange mineral deposits. They reported Native American accounts from near the epicenters and from further west. In ways both idiosyncratic and creative, early Americans attempted to convey and come to terms with these sudden and disruptive temblors. Accounts of the quakes demonstrate the blurred nature of expert and nonexpert discussions in the early nineteenth century. Because of the lack of clear consensus about the mechanisms or causes of earthquakes, people in borderland regions along the Ohio and Mississippi Valley became not simply witnesses but theorists of the dramatic seismicity they had experienced. Their attempts to record and explain events that overwhelmed them reveal a broadly-shared and vigorous culture of science in the early United States. This earlier history also highlights the surprising forgetting of the quakes in the late nineteenth century, a forgetting that took place for social and environmental as well as scientific reasons. The New Madrid quakes represent an event once taken for granted that receded almost into tall tale for the better part of a century.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Kiser, Eric
Schedule   Thu 4:15 PM / Oral
Room   Room 204/205
A Multi-Frequency Back-Projection Analysis of Recent Large Earthquakes
KISER, E., Harvard University, Cambridge, MA, kiser@fas.harvard.edu; ISHII, M., Harvard University, Cambridge, MA, ishii@eps.harvard.edu
We apply a back-projection technique to study the source parameters of large earthquakes that have occurred over the past decade using data from the High Sensitivity Seismograph Network and the Full Range Seismograph Network in Japan, and the Transportable Array in the United States. In order to investigate the frequency dependent characteristics of rupture, we back-project data filtered at multiple frequency ranges. In addition, for a subset of the large events, we combine multiple seismic arrays to improve resolution.The multi-frequency back-projection results reveal unexpected details about recent large earthquakes. For example, the February 27, 2010 Mw 8.8 Chile earthquake has three different rupture behaviors composing the event. The two subevents north of the epicentre have relatively fast rupture velocities (2.2 and 2.9 km/s) and are dominated by high-frequency (1-5 Hz) energy release. In contrast, the subevent south of the epicentre has a very slow rupture velocity (0.8 km/s) and mostly low-frequency (0.05-0.1 Hz) energy release. These results suggest that the dynamics of slip change along the strike of the subduction zone. In addition, spatial and temporal gaps in slip suggest triggering between different rupture segments.Additional complexities can be seen when analyzing the spatio-temporal relationship of results from high- (1-5 Hz) and intermediate-frequencies (0.5-1 Hz). These results demonstrate that high-frequency energy is released in front of intermediate-frequency energy in the direction of rupture. We interpret this result as “breaking” of the fault preceding slower slip due to reduced friction. This result points to the importance of thermal processes and fault lubrication, and suggests that the mechanisms of large earthquakes may be quite different than those of small events.
Session:Seismic Imaging: Recent Advancement and Future Directions
Presenter   Larmat, Carene
Schedule   Wed 5:30 PM / Oral
Room   Ballroom D
Validating 3D seismic velocity models using the Spectral Element Method.
LARMAT, C. S., Los Alamos National Laboratory, Los Alamos, NM, carene@lanl.gov; MACEIRA, M., Los Alamos National Laboratory, Los Alamos, NM, mmaceira@lanl.gov; ROWE, C. A., Los Alamos National Laboratory, Los Alamos, NM, char@lanl.gov
As seismic instrumentation, data storage and dissemination and computational power improve, seismic velocity models attempt to resolve smaller structures and cover larger areas aiming to improve the accuracy of source location and seismic event parameters. However, it is unclear how accurate these velocity models are. Model validation is typically done using resolution tests that assume the imaging theory used is accurate and thus only considers the impact of the data coverage on resolution. We present the results of a more rigorous approach to model validation via full three-dimensional waveform propagation using Spectral Element Methods (SEM). SEM is particularly well adapted to solve wave propagation in 3D complex Earth models since it is a high order finite element method with exponential convergence while maintaining the geometric flexibility of finite element methods necessary to consider topography features. We compare synthetics computed with SEM with records of the dataset to assess the quality of the models. We first validate 3D tomographic models for the Western USA generated using both ray-theoretical and finite-frequency methods. The Dynamic North America (DNA) Models of P- and S- velocity structure (DNA09-P and DNA09-S) use teleseismic body-wave traveltime residuals recorded at over 800 seismic stations provided by the Earthscope USArray and regional seismic networks. Preliminary results concerning one set of stations and one earthquake show that there is no noticeable improvement when considering the finite-frequency model versus the ray theoretical one, at least when we visually compare the waveforms. This initial computations resolved frequency down to 15s. Further investigation efforts are involving computation of misfit functions and use of statistic methods to extract rigorous general trends. We are also performing computations for other earthquakes, more stations and at higher frequency which the aim to study body wave arrivals.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Tuttle, Martitia
Schedule   Thu PM / Poster
Room   Ballroom B
Paleoseismic Constraints on Seismic Hazard of the Greater Toronto Region, Ontario, Canada
TUTTLE, M. P., M. Tuttle & Associates, Georgetown, ME, ; ATKINSON, G. M., University of Western Ontario, London, ON, Canada,
During a reconnaissance-level paleoliquefaction study, earthquake-induced liquefaction features were found along two rivers in the Greater Toronto region. Geologic relations of the features and radiocarbon dating of host sediments suggest that the liquefaction features formed during two, possibly three, different earthquakes: ~1 ka during the Late Holocene, 5-22 ka during the Middle Holocene-Late Wisconsin, and possibly ~42 ka during the Middle Wisconsin. In contrast, no liquefaction features were found east of Greater Toronto even though exposure was good and deposits are similar to those where liquefaction features occur. The apparent absence of liquefaction features to the east of Greater Toronto suggests that the eastern area may have been subjected to lower levels of ground shaking during the paleoearthquakes. An evaluation of scenario earthquakes suggests that moderate-to-large earthquakes (M > 6) located in the Greater Toronto region or to its southwest could have produced the observed distribution of liquefaction features. Although it may be incomplete due to the limited area searched and fluctuations in lake level, the Late Quaternary record of paleoearthquakes indicates that magnitude > 6 earthquakes have caused strong ground shaking in Greater Toronto at least twice in the past 22 kyr, suggesting a maximum average recurrence time of 10 kyr for such events. These findings begin to provide geologic constraints on seismic hazard for the region, but significant uncertainties remain regarding the sources, magnitudes, and recurrence times of large earthquakes that could be reduced with further study southwest of Greater Toronto. In addition, we compare the preliminary paleoliquefaction-based recurrence times with historical seismicity rates to better constrain magnitude-recurrence parameters in the region.
Session:Seismic Sources and Parameters
Presenter   Dewey, James
Schedule   Wed AM / Poster
Room   Ballroom B
Variations of mb(PDE): 1976 -- 2010
DEWEY, J. W., U.S. Geological Survey, Denver, CO, jdewey@usgs.gov; PRESGRAVE, B. W., U.S. Geological Survey, Denver, CO, presgrave@usgs.gov; EARLE, P. S., U.S. Geological Survey, Denver, CO, pearle@usgs.gov
We analyze temporal changes in mb(PDE), the short-period teleseismic P-wave magnitude that is published in the PDE bulletin of the USGS/National Earthquake Information Center. For the period 1976 – 2010, mb(PDE) has experienced long-term drifts of several tenths of a magnitude unit (m.u.) with respect to other magnitude types. For moderate and large shallow-focus earthquakes to which both mb(PDE) and Mw(Global CMT Project, LDEO) have been assigned, average values of mb[Mw] in 2010 were near their maximum for the entire 1976 – 2010 period. Considering worldwide shallow-focus shocks of Mw(GCMT) > 6.0, mb(PDE) for earthquakes in 2010 were on average about 0.3 m.u. higher than mb(PDE) of shocks occurring during late 1997 – early 1998, for earthquakes having the same value of Mw(GCMT). Late 1997 – early 1998 was a time in which globally averaged mb[Mw] was near a minimum for the 1976-2010 study period. To first order, from 0.05 to 0.10 m.u. of the drift of average mb[Mw] can be attributed to temporal changes in the distribution of stations that observe mb, coupled with station-specific biases that reflect site-amplification effects or anomalies in station instrumentation. Also to first order, about 0.1 m.u. of the global drift of average mb[Mw] is associated with temporal changes in the geographic locations of highest seismic activity. Higher order effects, such as mb[Mw] drift that reflects coupling between the changing global station network and changes in the locations of highest seismic activity, are likely. A post-2009 increase of average global mb[Mw] by 0.1 m.u. for shallow-focus earthquakes of Mw(GCMT) > 6.0 is a consequence of changes in mb processing at the USGS National Earthquake Information Center, including a change in the filter through which amplitudes are measured, to make the mb(PDE) procedure conform to IASPEI recommendations, and the replacement of manual amplitude/period measurements with automatic measurements.
Session:Earth Structure Observations and Theory
Presenter   Murphy, Rachel
Schedule   Thu PM / Poster
Room   Ballroom B
What Can S-waves Tell Us about Magma Storage beneath the Katmai Volcanic Complex?
MURPHY, R. A., University of Wisconsin - Madison, Madison, WI, rmurphy@geology.wisc.edu; THURBER, C. H., University of Wisconsin - Madison, Madison, WI, clifft@geology.wisc.edu; PREJEAN, S. G., USGS Alaska Volcano Observatory, Anchorage, AK, sprejean@usgs.gov; ZHANG, H., Massachusetts Institute of Technology, Cambridge, MA, hjzhang@mit.edu
We present an S-wave velocity model and revised hypocenter locations using both P- and S-wave arrivals for the Katmai volcanic cluster on the northern Alaska Peninsula. The data come from the Alaska Volcano Observatory’s permanent network of one- and three-component instruments along with a temporary array of three-component instruments densely spaced in the Katmai Pass region. S-wave arrival picks were made both by hand and using an automated higher-order-statistics picker developed in Matlab. Velocity models and earthquake relocations were computed using the double-difference technique for tomography and event relocation. These tomographic results, in combination with a previously developed P-wave velocity model, support a model of localized magma storage spatially coincident with the volcanic edifices of Martin, Mageik, Trident/Novarupta, and Katmai. This is in contrast to the one large magma storage zone centered on Katmai Pass that has previously been proposed in geophysical studies. Earthquake relocations indicate that seismic activity in the region is focused in four clusters, again associated with Martin, Mageik, Trident/Novarupta, and Katmai. This points towards separate magma plumbing systems at least at shallow depths. The seismicity clusters primarily consist of linear features located just outside of the low velocity regions, although the geometry of the seismicity associated with Martin is more scattered in both map view and cross section. We additionally investigate the effect of the ray-tracing technique used on the relocations. Hypocenter depths are consistently found to lie between 3.5 and 5 km below sea level regardless of the algorithm used; for most individual events, this is 1 to 2 km deeper than the catalog location.
Session:Multivariate Approaches to Earth’s Seismic Structure
Presenter   Maceira, Monica
Schedule   Thu 8:30 AM / Oral
Room   Ballroom E
Advanced Multivariate Inversion Techniques and its Application to Northwest China Velocity Structure
MACEIRA, M., Los Alamos National Laboratory, Los Alamos, NM, mmaceira@lanl.gov; ZHANG, H., Massachusetts Institute of Technology, Cambridge, MA, hjzhang@mit.edu; ROWE, C. A., Los Alamos National Laboratory, Los Alamos, NM, char@lanl.gov
We implement and apply a method to jointly invert surface-wave group velocities, gravity observations, and body-wave arrival times. Surface wave dispersion measurements are primarily sensitive to seismic shear-wave velocities, but at shallow depths it is difficult to obtain high-resolution velocities and to constrain the structure due to the depth-averaging of the more easily-modeled, longer-period surface waves. Gravity inversions have the greatest resolving power at shallow depths, and they provide constraints on rock density variations. Addition of seismic travel-time data helps to constrain the shear wave velocities both vertically and horizontally in the model cells crossed by the ray paths. To combine the different geophysical datasets into a common system, we design an optimal weighting scheme that is based on relative uncertainties of individual observations, their sensitivities to model parameters, and the trade-off of different data fitting. Incorporation of both P and S body wave travel times allows us to invert for both P and S velocity structure, capitalizing on empirical relationships between both wave types’ seismic velocities with rock densities, thus eliminating the need for ad hoc assumptions regarding the Poisson ratios. We apply the method to investigate the seismic velocity structure of two large central Asia sedimentary basins: the Tarim and Junggar. The basins have thick sediment sections that produce substantial regional gravity variations (up to several hundred mgal). We combine GRACE gravity anomalies with high-resolution surface-wave slowness tomographic maps in the period range between 8 and 100 s. The seismic body wave arrival times are retrieved from Los Alamos National Laboratory seismic database. Preliminary results show high upper-mantle shear velocities beneath the Tarim basin and suggest differences in lower-crust and upper-mantle shear velocities between the eastern and western Tarim.
Session:Long-term Behavior of Faults and Earthquake Hazards in Intraplate Continental Regions
Presenter   Decker, Kurt
Schedule   Thu 9:15 AM / Oral
Room   Ballroom C
Assessing Maximum Credible Earthquake (MCE) Magnitudes for a Slow Intra-Plate Fault System in the Vienna Basin, Austria
DECKER, K., University of Vienna, Vienna, Austria, kurt.decker@univie.ac.at; HINTERSBERGER, E., University of Vienna, Vienna, Austria, esther.hintersberger@univie.ac.at
Assessing the MCE for a region is an important step in seismic hazard assessment. In areas of high seismicitiy and long historic records, the probability is relatively high that the MCE is included in the earthquake catalog. In regions with low or absent historic seismicity, however, the MCE must be determined from geological data. In the Vienna Basin, moderate seismicity (Imax/Mmax=8/5.2) concentrates on a left-lateral strike-slip fault, which is connected to several normal splay faults. The strike-slip fault includes significant fault bends of 20°–35° delimiting geometrical fault segments. The bends are expected to act as impediments during dynamic rupture propagation. Hence, fault segment dimensions are used for constraining the maximum fault surfaces likely to break during an earthquake. The splay faults do not show any historical seismicity. Geological and morphological data, however, proof that they moved at velocities of ≤0.1mm/y during the Quaternary. Active fault maps show six major very slow normal faults branching from releasing bends of the strike-slip fault and compensating fault-normal extension in a transtensional strain environment. In order to assess MCE magnitudes for this complex tectonic setting on the background of earthquake data spanning a time of <500yrs (i.e., shorter than the recurrence times of the strongest earthquakes) we choose a deterministic approach using a 3D fault model derived from reflection seismic to quantify the sizes of potential single-event rupture zones. The model accounts for kinematic fault segmentation. Fault surfaces of strike-slip segments vary from 55km to 400km , those of the normal splay faults from 100 to 700km . Empirical relations confirm that these areas are sufficiently large to create earthquakes with M=6.0-6.8. Our MCE estimates are supported by paleoseismological data obtained from one of the splay faults showing that the fault released earthquakes with M=6.3-7.0 at recurrence intervals of about 20ky.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Johnston, Arch
Schedule   Wed 3:15 PM / Oral
Room   Ballroom C
Pawpaw Creek and Ridgeley Ridge: Overlooked Uplift Constraints on 1811-1812 New Madrid Faulting
JOHNSTON, A. C., CERI, The University of Memphis, Memphis, TN, ajohnstn@memphis.edu; PATTERSON, G., CERI, The University of Memphis, Memphis, TN, glpttrsn@memphis.edu; MORAN, N. K., CERI, The University of Memphis, Memphis, TN, nkmoran@memphis.edu
Pawpaw Creek exits the Reelfoot bluffs south of Reelfoot Lake and - currently - enters Running Reelfoot Bayou (RRB), flowing south to the Obion River. This has not always been so. In the original survey of these lands - the 1785 Henry Rutherford survey for the State of North Carolina - Pawpaw Creek flowed westward across the Mississippi River floodplain to join Reelfoot Creek at the "Pawpaw Waterhole," currently located on the crest of Ridgeley Ridge, some 12-15 ft above the RRB. The strong implication is that, post-1785, Ridgeley Ridge and hence the bed of Pawpaw Creek rose a minimum of 4-5 meters, most likely during the sequence of major New Madrid earthquakes in the winter of 1811-12. Such a fault throw is probably too great to result from aftershocks. We argue it is best interpreted as the SSE continuation of the mainshock Reelfoot fault rupture of 7 February 1812 that dammed off Reelfoot Creek, diverting it to the RRB. This SSE continuation of the Reelfoot fault may extend as far as across Obion River, north of Dyersburg, TN, as suggested by current seismicity. Our main conclusion from this work is that a major portion, perhaps all, of Ridgeley Ridge was uplifted during the 1811-1812 earthquakes. This is contrary to some previous studies (eg, D. Russ, 1982; R. Stearns, 1979) based on more indirect, even ambiguous observations that conclude Ridgeley Ridge did not rise in the 1811-12 sequence. If our interpretation is correct, it has important implications for stable-continental-region earthquake source scaling and Mmax assignment for the central United States.
Session:Geometry effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Presenter   Assimaki, Dominic
Schedule   Wed 5:00 PM / Oral
Room   Room 204/205
Three-dimensional topographic amplification of seismic ground motion on an idealized convex feature
ASSIMAKI, D., Georgia Institute of Technology, Atlanta, GA, dominic@gatech.edu; KALLIVOKAS, L., University of Texas at Austin, Austin, TX, loukas@mail.utexas.edu; MOHAMMADI, K., Georgia Institute of Technology, Atlanta, GA, kamimohamadi@gatech.edu
Topography effects are associated with the presence of strong topographic relief, and documented observations during strong seismic events have shown that structures on the tops of hills, ridges, and canyons had suffered greater damage than similar structures at the hill bases or at ground level. Various records confirm the macroseismic observations, indicating systematic amplification of seismic motion over convex topographies. Though there is qualitative agreement between theory and observations on topography effects, quantitative discrepancies clearly exist: numerical predictions of crest-to-base amplification factors rarely exceed the value of 2, while amplification values observed in the field are as high as 10. By and large, to date, most studies on topography effects focus on the response of idealized two-dimensional (2D) features, ignoring the potentially detrimental role of three-dimensional (3D) ray focusing in incident seismic motion amplification.In this paper, we investigate the role of 3D seismic wave focusing and scattering in predicting topographic amplification. We demonstrate first the effects of 3D wave propagation using mine-induced seismicity records from a recently instrumented hill in Utah. We next conduct a systematic parametric investigation of the seismic response of an idealized convex feature on the surface of a homogeneous elastic halfspace, and quantify the role of topographic geometry and ground motion characteristics in the predicted ground surface response. By comparing the amplification on the surface of a 2D wedge-type to the corresponding 3D pyramid-type geometry, we identify the conditions under which 3D effects may not be ignored when predicting topographic amplification.
Session:Combining Geodetic and Seismic Measurements
Presenter   Chao, Kevin
Schedule   Fri PM / Poster
Room   Ballroom B
Comparisons of Triggered Tremor in California
CHAO, K., Georgia Institute of Technology, Atlanta, GA, kevinchao@gatech.edu; PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng@gatech.edu; FABIAN, A., University of South Carolina, Columbia, SC, fabiana@mailbox.sc.edu; OJHA, L., University of Arizona, Tucson, AZ, luju@email.arizona.edu
“Non-volcanic” tremor is a seismic signal observed away from volcanoes, and is characterized with long durations and no clear body wave arrivals. Recent studies have found that non-volcanic tremor can be triggered instantaneously during the surface waves of large teleseismic events in California, Japan, Cascadia, and Taiwan. However, it is still not clear how widespread the triggering phenomenon is, and what are the necessary conditions for tremor to occur. We conduct a systematic search of tremor in California triggered by teleseismic earthquakes with Mw ≥ 7.5 between 2001 and 2010. We identify triggered tremor by visually examining 2-8 Hz band-pass-filtered seismograms recorded by regional seismic networks around the San Jacinto fault in southern California (SC) and the Central Calaveras fault in northern California (NC). Out of the 42 events, only the 2002 Mw7.8 Denali Fault earthquake have triggered clear tremor in both regions. Tremor is excited by the Love waves when the major fault is sheared in the right-lateral sense, and become further intensified during the large-amplitude Rayleigh waves. This is consistent with a model of simple frictional response to driving stress as inferred from previous studies of triggered tremor in central California (CC) and elsewhere. In addition, we quantify the background noise level of each teleseismic main shock in CC, SC, and NC and compare the difference of triggering potential in these three regions. We found that the signal to noise ratio of ~1.5 is needed for the triggered tremor to be visually identified, and that the background noise level in SC and NC is higher than in CC. However, the lack of widespread triggering of tremor in SC and NC cannot be solely explained by the background noise levels and/or the difference in network quality, but rather suggests different ambient tremor rate or tremor triggering threshold in these regions.
Session:Probabilistic Methods in Tectonophysics and Seismic Hazard Assessment
Presenter   Scharer, Kate
Schedule   Fri AM / Poster
Room   Ballroom B
Comparison three paleoseismic chronologies from the Pallett Creek, CA site on the San Andreas fault: methods and implications
SCHARER, K., Appalachian State University, Boone, NC, scharerkm@appstate.edu; BIASI, G., Univeristy of Nevada, Reno, NV, glenn@unr.edu; WELDON, R., University of Oregon, Eugene, OR, ray@uoregon.edu
The Pallett Creek paleoseismic record, originally published by Sieh and colleagues, provides important constraints on the rupture history of the San Andreas fault and includes nine paleoearthquakes in the last 1500 years. Existing chronologies for this record include Sieh et al. (1989) which estimated earthquake ages based on the stratigraphic position of earthquake horizons relative to dated layers, and Biasi et al. (2002) which developed a probability distribution function (PDF) for each earthquake age using a Bayesian approach that employs stratigraphic ordering and sedimentologic constraints. Both studies were based on conventional radiocarbon dates that required over 7 g of carbon in each sample. Each sample would have included varying (but unknown) amounts of in situ plant material, recalcitrant charcoal, and partially decomposed roots and the relative amounts of each component could change the age of the sample by hundreds of years. Advances in radiocarbon techniques since the late 1980’s have decreased the amount of carbon needed for each sample to 2 mg, which permits targeted dating of discrete samples with known relationships to the stratigraphic record (e.g., charcoal dates are considered maximum ages). We present 65 new radiocarbon dates including 46 from individual charcoal pieces, 17 bulk organic dates, and 2 macrofossil dates, and then apply a similar Bayesian approach to determine paleoearthquake PDFs. Overall, the new layer ages are similar to the original ages, but individual earthquake ages changed by as much as 120 years. The new record is visually more regular than suggested in the earlier records, coincident with a reduction in the coefficient of variation (COV) from ~0.8 to 0.6. We explore the significance of these results by examining the affect of paleoseismic dating uncertainties (layer age, sedimentation rate, and Bayesian refinement) on the COV, and present non-parametric tests that explore the recurrence behavior of each record.
Session:Geometry effects in Ground Motion: Focusing, Scattering and Waveguides of Seismic Rays in the Near-surface
Presenter   Huerta-Lopez, Carlos
Schedule   Wed AM / Poster
Room   Ballroom B
The Puerto Rico MW 5.8 Earthquake of May 16, 2010: Distribution of Peak Ground Acceleration and Intensity in the Puerto Rico Island
HUERTA-LOPEZ, C. I., Research Center and Higher Education at Ensenada (CICESE), Ensenada, Baja California, Mexico and University of Puerto Rico (PRSMP) at Mayaguez, Puerto Rico, m-huerta@alumni.utexas.net; DE BASABE-DELGADO, J. D., Research Center and Higher Education at Ensenada (CICESE), Ensenada, Baja California, Mexico, jonas@cicese.mx; MARTINEZ-CRUZADO, J. A., University of Puerto Rico at Mayaguez, Mayaguez, PR, jose.martinez44@upr.edu; ROMAN-BATISTA, R. E., University of Puerto Rico at Mayaguez, Mayaguez, PR, ingromanruth@hotmail.com; CARO-CORTES, J. A., University of Puerto Rico at Mayaguez, Mayaguez, PR, andres.caro@upr.edu; SUAREZ-COLCHE, L. E., University of Puerto Rico at Mayaguez, Mayaguez, PR, luis.suarez3@upr.edu
An earthquake of MW 5.8 occurred in the northwest region of Puerto Rico Island (18.4o Lat, -67.07o Lon, and focal depth 113.1 km) at 05:16:10 UTC on May 16, 2010. An analysis and discussion is presented with the aim to explain the anomalous distribution of peak ground motions, which may be associated not only by local site effects due to the presence of soft soils.In the city of Añasco, which is located at approximately at 15 Km from its epicenter, an intensity (MMI) of V was reported, while in some cases hardly reach the value of III at closer epicentral distances. An instrumental intensity of VII was estimated in the area of Utuado town located roughly at 45 Km from the epicenter.The observed maximum peak ground acceleration was: (i) 0.0651 of g at Añasco (AÑS1 station, located at an epicentral distance of 15 km in alluvial soil), and (ii) 0.2301 of g at station UTD2 located at an epicentral distance of 42 km on rock. The instrumental intensity (MMI) estimated with Wald et al., (1999) relationship was V and VII, respectively for these two previously described sites.This earthquake was widely felt in Puerto Rico, the eastern Dominican Republic, and The Virgin Islands. It was recorded also by 59 stations of the Puerto Rico Strong Motion Program (PRSMP) providing a reliable set of acceleration records distributed around the island. According to the USGS Centroid Moment Tensor solution, this earthquake occurred in an inclined seismic zone that dips south from the Puerto Rico Trench and that consists of subducted lithosphere of the North America plate. Earthquakes that have focal-depths between 70 and 300 km, are commonly termed "intermediate-depth" earthquakes and typically cause less damage on the ground surface above their foci than is the case with similar magnitude shallow-focus earthquakes. Large intermediate-depth earthquakes may be felt at great distance from their epicenters.
Session:Creative Wavefield Recording and Analysis
Presenter   Kendall, Lauren
Schedule   Fri 10:45 AM / Oral
Room   Ballroom E
Testing Rotational Seismometers with Array Computed Rotations
KENDALL, L. M., University of Memphis, Memphis, TN, lmkndall@memphis.edu; LANGSTON, C. A., University of Memphis, Memphis, TN, clangstn@memphis.edu; LEE, W. H. K., USGS, Palo Alto, CA, lee@usgs.gov; LIN, C. J., Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ; LIU, C. C., Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan,
On 4 March, 2008, two explosions were set off in northeastern Taiwan associated with a TAIGER (TAiwan Integrated GEodynamics Research) long-range refraction experiment. The first one (N3P) used 3000 kg of explosives and the second (N3) used 750 kg. Thirteen strong motion seismic stations were installed close to the explosions including an 11 station gradiometric array with a sensor spacing of 5 m from each other and an average distance of 500 m from the sources. Each station contained an accelerometer and 5 also contained eentec R-1 rotational sensors. The objective of this experiment was to test the response of these experimental rotational sensors against calculated rotations about the local x, y, and z axes using wavefield gradients computed with the array data. Computed array rotations have little variation across the array but the point rotation measurements obtained from individual rotation sensors show large deviations with each other and with the array rotations. A computation of cross-correlation of these array computed rotations and point rotation measurements was calculated, and the normalized maximum cross-correlation coefficient for each station set was relatively low. These comparisons suggest that either point rotation measurements are actually highly variable in space because of very local site conditions and instrument installation practices or that a method be developed to accurately determine the rotation instrument response before installing these instruments in the field.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Ogwari, Paul
Schedule   Thu AM / Poster
Room   Ballroom B
Effects of Style of Faulting on Earthquake Ground Motions in NMSZ
OGWARI, P. O., University of Memphis, CERI, Memphis, TN, opogwari@memphis.edu; HORTON, P. S., University of Memphis, CERI, Memphis, TN, shorton@memphis.edu; WITHERS, M., University of Memphis, CERI, Memphis, TN, mwithers@memphis.edu; CRAMER, C. H., University of Memphis, CERI, Memphis, TN, ccramer@memphis.edu
We investigate the effects of style of faulting on earthquake ground motion in the New Madrid Seismic Zone (NMSZ). Style of faulting has not been considered in previous ground-motion relations in Eastern North America (ENA) although it has been found to produce systematically different ground motion in recent western U.S. ground motion models that distinguish between reverse and strike-slip earthquakes. We undertake a detailed analysis of local waveform data using a multistage processing method (e.g. Raoof et al., 1999; and Malagnini et al., 2000) to produce empirical attenuation relations for frequencies between 1 and 16Hz. The dataset consists of 1350 local events of magnitude 1.6≤M≤4.3 recorded at an hypocentral-distance ranging from 5.6 to 145km. Earthquake focal mechanisms are from two recent studies (Johnson et al., 2008; and Horton, 2008). The modeling procedure yields geometrical spreading as a piecewise continuous function of distance, parameterized as ra, within a discrete number of distance ranges. Preliminary results show r-1 geometrical spreading with Q(f)=660f0.35 within the first 60 km hypocentral distance. Beyond 60 km distance, the geometrical spreading changes to r0.5. This is comparable to previous relations in ENA although the change in geometrical spreading typically occurs at 70 km instead of 60 km. This could be due to a proposed high velocity rift pillow, lying above the Moho within Mississippi Embayment, which could reduce the crustal thickness hence travel time of critically refracted rays producing pseudo-Moho post-critical reflections at a shorter distance. Of particular interest are preliminary results indicating a faster decay of the amplitude with distance for reverse fault events, and slower decay for strike-slip fault events, compared to the average attenuation of the region at frequencies greater than 8Hz. At lower frequencies, no difference is discerned for the two styles of faulting.
Session:Combining Geodetic and Seismic Measurements
Presenter   Mataracioglu, Mehmet Onur
Schedule   Fri PM / Poster
Room   Ballroom B
Wave Gradiometry of the Mw=8.8 Maule, Chile Earthquake Using Absolute Displacement Seismogram from High-Rate GPS for the Western U.S.
MATARACIOGLU, M. O., University of Memphis - CERI, Memphis, TN, mmtrcglu@memphis.edu; SMALLEY, R., University of Memphis - CERI, Memphis, TN, rsmalley@memphis.edu; LANGSTON, C. A., University of Memphis - CERI, Memphis, TN, clangstn@memphis.edu; DAVIS, J. P., University of Memphis - CERI, Memphis, TN, jpdavis@memphis.edu
We compute and compare the wave gradiometry parameters of azimuth, slowness, geometrical spreading change, radiation pattern change, and horizontal strains from 1 Hz. high-rate GPS (HRGPS) displacement time series for the February 27, 2010, Mw=8.8 Chile earthquake for two different regions in the western United States. Then, we compute the wave attributes of propagating Love wave using wave gradiometry of the absolute displacement seismograms for a site near the Salton Sea and another around San Francisco Bay. The wave gradiometry results show that displacement gradients and, thus, shear strain, in northern California was anomalously high compared to displacement gradients of the Love wave near the Salton Sea. This resulted in unrealistic low estimates of the phase velocity in northern California for 120 seconds period Love waves. We investigate this anomaly by comparing wave gradiometry results determined from arrays of broadband seismometers near both regions to first see if the GPS results are consistent with the seismic data and then to investigate the influence of ocean/continent boundary that could cause multipathing, violating a principal assumption in wave gradiometry analysis. Nevertheless, the use of HRGPS data with seismic array processing represents a new use of this unique data set that should yield useful information about earth structure and source processes for high amplitude seismic signals.
Session:Seismic Sources and Parameters
Presenter   Kilb, Debi
Schedule   Wed 3:30 PM / Oral
Room   Ballroom E
Surface Icequakes from the Gornergletscher in Switzerland
KILB, D., Scripps Inst. of Oceanography, La Jolla, CA, dkilb@ucsd.edu; WALTER, F., Scripps Inst. of Oceanography, La Jolla, CA, fabian.t.walter@gmail.com; ROUX, P. F., CGGVeritas, Massy, France, pfrancois.roux@gmail.com; DEICHMANN, N., Swiss Seismological Service, ETH, Zurich, Switzerland, deichmann@sed.ethz.ch; FUNK, M., Laboratory of Hydraulics, Hydrology and Glaciology, ETH, Zurich, Switzerland, funk@vaw.baug.ethz.ch
We study surface icequakes (driven by surface crevasse openings) on Gornergletscher, Switzerland’s second largest glacier. These data were recorded over 1-2 month periods in the summers of 2004, 2006 and 2007. Of the >175,000 cataloged events, we restrict our analysis to surface events within the footprint of our network and we discard data from time windows when the full network was not functioning. We apply the method of Roux et al 2010, which is automated to assess waveform cross-correlation values of pairs of vertical component recordings of the Rayleigh wave phase. Requiring correlation values of 95% or above, we locate 14,528 surface icequakes. We find the distribution of icequakes form distinct clusters, often appearing as lineations mapping surface crevasses. For each year of data, we bin the icequakes according to their spatial distribution. These distributions vary, sometimes being uniformly distributed along the crevasse and sometimes concentrating near the crevasse tips. In the 2006 and 2007 data we find a strong diurnal signal in the seismicity, exhibiting favoritism for icequake activity during the day when there is more melt water and glacier flow is more rapid. We also find the individual crevasses, or data subsets, often show a preferred ‘time of day’ for rupture. The regions of ‘daytime’ rupture tend to be spatially separated from those of ‘nighttime’ rupture, a pattern repeatable in all three years of data. We propose this favoritism for day or night rupture is a signature of differences in basal conditions (e.g., basal water pressure, basal topography). For example, one bed region may receive more water from the diurnal surface melt than the other. Another possibility is that diurnal variations in glacier flow speed combined with the local ice flow pattern (i.e., ‘turning a corner’) shift the regions of maximum tensile stresses. If true, this would indicate that surface fracturing depends not only on stress, but also on stress change.
Session:Broadband Ground-Motion Time Series Generation
Presenter   Olsen, Kim
Schedule   Wed 11:00 AM / Oral
Room   Ballroom E
Goodness-of-fit Criteria for Broadband Synthetic Seismograms, with Application to the 2008 Mw 5.4 Chino Hills, California, Earthquake
OLSEN, K. B., San Diego State University, San Diego, CA, kbolsen@sciences.sdsu.edu; MAYHEW, J. E., San Diego State University, San Diego, CA, ; WITHERS, K., San Diego State University, San Diego, CA,
We present a new goodness-of-fit (GOF) measure for broadband ground motion time histories. As is the case with the GOF measure proposed by Anderson (2004), our method includes a set of user-weighted metrics such as peak ground motions, response spectrum, the Fourier spectrum, cross correlation, and energy release measures. The scale for the GOF ranges from near 0 to 100 (perfect fit). We apply the method to synthetic seismograms for the 2008 Mw5.4 Chino Hills, CA, earthquake, simulated in two different velocity models: CVM-4 and CVM-H6.2, and the spatial distributions of GOF values are presented as maps. The two CVMs generate generally similar (and generally high) long-period (0.1-0.5 Hz) levels of GOF for this event. However, parts of Orange and Riverside counties and western Mojave Desert locations produce less favorable GOF values for both CVMs, and CVM4 tends to be more accurate at most basin sites. These results provide guidance for improvement in accuracy of the velocity structure. The long-period synthetics for Chino Hills were combined with high-frequency scattering functions to generate broadband synthetics (0-10Hz) using the method by Mai et al. (2010). At shorter periods, the GOFs fall above our general acceptance level (as well as that proposed by Anderson, 2004) at about 2/3 of the selected sites for the event. In addition to the metrics used for the long-period synthetics, we computed the GOF for the Chino Hills event including an additional metric with specific interest for structural engineers, the ratios of inelastic/elastic displacements (IE ratios). We find a good fit between IE ratios for synthetics and data at long periods, which degrades at shorter periods, in agreement with Baker and Jayaram, 2008. It is possible that the use of site-specific parameters (kappa, scattering coefficient) may improve the fit for the shorter periods of the synthetics.
Session:Verification Science
Presenter   Slinkard, Megan
Schedule   Fri AM / Poster
Room   Ballroom B
Parameter Selection in Waveform Correlation
SLINKARD, M., Sandia National Laboratories, Albuquerque, NM, meresor@sandia.gov; CARR, D., Sandia National Laboratories, Albuquerque, NM, dbcarr@sandia.gov
For nuclear explosion seismic monitoring, major earthquake aftershock sequences can be a significant problem, because each event must be processed correctly to insure that no nuclear tests are missed. Fortunately, the high degree of waveform similarity expected within aftershock sequences offers a way to more quickly and robustly process these events than is possible using traditional methods (e.g. STA/LTA detection).We explore how waveform correlation can be incorporated into an automated event detection system to improve both the timeliness and the quality of the resultant bulletin. Last year we presented our Waveform Correlation Detector and results from processing 3 aftershock sequences. Our system compares incoming waveform data to a continuously updating library of known events. Incoming waveform data that correlates above a specified threshold with a library event is marked as a repeating event. In this manner, between 3% and 92% of the events in a sequence were recognized as repeating events. This year, we explore how to adaptively and in real time determine appropriate parameters such as window length, filter bands, and correlation thresholds. These parameters are crucial to obtaining maximum benefit from the WCD in an operation system. Our system is designed to begin running shortly after a large mainshock, and adaptively determine parameters appropriate to the swarm as it runs. We present results from the adaptive WCD and demonstrate the effect of parameters on the effectiveness of waveform correlation.
Session:Ground Motion Attenuation Modeling: Functional Form, Input Parameters, Standard Error and Testing Criteria
Presenter   Chapman, Martin
Schedule   Wed 2:45 PM / Oral
Room   Room 204/205
Modeling of Near-Source Geometrical Spreading and Vertical/Horizontal Component Amplitudes for Eastern North America
CHAPMAN, M. C., Virginia Tech, Blacksburg, VA, ; GODBEE, R. W., Virginia Tech, Blacksburg, VA,
Geometrical spreading and the relative amplitudes of high-frequency vertical and horizontal components of ground motion within 120 km of the source were examined using a full wavefield simulation method. One-dimensional, horizontally layered velocity models representative of the Appalachian region and the Atlantic coastal plain were used, in conjunction with point-source and finite-fault sources. Simulations were done for a grid of receivers with 2-4 km spacing to 120 km, for a range of focal depths, and for strike-slip and reverse focal mechanisms. The modeling shows apparent geometrical spreading of the geometric mean of randomly oriented horizontal component amplitude, averaged over all azimuths, significantly exceeding the ideal case for body waves in a homogeneous whole space, for hypocenter distances less than approximately 60 km. The behavior of the vertical component is different from the horizontal: vertical component apparent geometrical spreading near the epicenter is much greater, and is dependent on focal mechanism and source depth. The vertical component amplitude versus distance trend flattens in the distance range 60 to 120 km. This is due to the effect of the free surface on the vertical component of direct Sv waves, which reduces amplitudes for large angles of incidence, leading to a situation where post-critical reflections from the mid-lower crust and Moho control the vertical component amplitude in the 60-120 km hypocenter distance range. Near-source vertical component amplitudes averaged over all source-receiver azimuths are less than azimuthally averaged geometric mean horizontal motions for strike-slip faults. However, at distances within a few tens of kilometers from the epicenter of reverse faults, the modeled vertical component amplitude equals or exceeds that of the mean horizontal.
Session:Recent Advances in Understanding Scaling Characteristics: How Similar Are Small and Large Earthquakes?
Presenter   Lozos, Julian
Schedule   Thu 4:45 PM / Oral
Room   Room 204/205
The Effects of D0 on Rupture Propagation on Geometrically-Complex Faults
LOZOS, J. C., University of California, Riverside, Riverside, CA, jlozo001@ucr.edu; DIETERICH, J. H., University of California, Riverside, Riverside, CA, dieterichj@ucr.edu; OGLESBY, D. D., University of California, Riverside, Riverside, CA, david.oglesby@ucr.edu
Laboratory studies show that fault friction drops from a static to a dynamic value over a short slip weakening distance D0. In earthquake models, rupture nucleation and propagation are strongly affected by D0, but appropriate values for modeling natural faults are uncertain. We use a 2D finite element method to model the effect of D0 on rupture propagation through two strike-slip fault geometries: connected stepovers, with two parallel segments joined at a set angle by a linking segment of variable length, and disconnected stepovers, with two parallel segments with a set overlap and variable separation between them. Each geometry poses different problems. In the disconnected case, propagation requires rupture to renucleate on the second fault segment, which depends on a critical patch size that is determined by D0. In the connected case, in addition to requiring that a critical patch size be reached on each segment, there is also the issue of propagation through a segment with a different static and dynamic favorability relative to the regional stress field. Extensional and compressional cases are modeled for both stepover types. We simulate earthquakes in these systems using five values for D0. We test several stress states, to determine whether the same behaviors occur with both supershear and subshear rupture velocity, and whether the specific intensity of the regional stress field affects scaling. We find that, regardless of rupture velocity or stress state, smaller D0 allows propagation through larger geometrical discontinuities, but that maximum propagation length/width does not scale linearly with D0. Nonlinearity is likely controlled by whether the area of static stress change induced by rupture on the nucleating segment exceeds the critical patch size needed for rupture on the next segment. We find that increasing the absolute intensity of the regional stress field increases maximum propagation length/width, but this scaling relationship also is not linear.
Session:Strain Accumulation Inside Continents: Observations, Uncertainties, and Models
Presenter   Hetland, Eric
Schedule   Thu 3:45 PM / Oral
Room   Ballroom C
Models of Interseismic Strain Accumulation and Earthquake Activity in Intercontinental Fault Zones
HETLAND, E. A., University of Michigan, Ann Arbor, MI, ehetland@umich.edu; MEDINA LUNA, L., University of Michigan, Ann Arbor, MI, lmedina@umich.edu
It is most commonly assumed that geodetic measurements near active faults record surface deformation due to strain accumulation on those faults. In the standard model of interseismic deformation, the concentration of strain rates measured across a fault depends on both the rate at which the fault is being loaded (i.e., the fault slip-rate) and the depth of the fault over which strain is accumulating (i.e., the locking depth). This standard model is often used in its elastic limit, where the steady viscoelastic relaxation time of the ductile lithosphere (lower crust and upper-most mantle) is much longer than the characteristic repeat time of earthquakes. When the steady relaxation time of the lithosphere is shorter than the earthquake repeat time, strain rates across the fault decrease throughout the interseismic period. For a steady relaxation time significantly shorter than the repeat time, deformation following an earthquake is due solely to that earthquake and deformation long after the earthquake is simple shear. It is important to note that the standard interseismic model assumes that the fault system is in a “mature” state, meaning that it has “spun-up” by repeated fault ruptures. The time required for a fault system to mature is proportional to the time-scale of the steady component of viscoelastic relaxation. When geodetically inferred fault slip-rates are lower than those inferred geologically, a low viscoelastic relaxation time of the lithosphere is often appealed to. However, an alternative consideration is that the fault is not mature, and thus that the standard model is inapplicable to that fault. In this presentation, we explore the applicability of the standard interseismic deformation model to the New Madrid seismic zone and the region of the 2008 Wenchuan, China earthquake, two regions where geodetic surveys indicated low levels of interseismic strain accumulation on the faults.
Session:Integrating Geodynamic, Structure and Deformation Studies of the Seismogenic and Transition Zones in Subduction Zones and Other Margins
Presenter   Chao, Kevin
Schedule   Thu PM / Poster
Room   Ballroom B
Deep Tremor Activities beneath the Central Range in Taiwan and their Relationship to Local, Regional, and Teleseismic Earthquakes
CHAO, K., Georgia Institute of Technology, Atlanta, GA, kevinchao@gatech.edu; PENG, Z., Georgia Institute of Technology, Atlanta, GA, zpeng@gatech.edu; WECH, A., Victoria University of Wellington, Wellington, New Zealand, Aaron.Wech@vuw.ac.nz; TANG, C., National Chung Cheng University, Chia-Yi, Taiwan, iori897@gmail.com; LIN, C., Academia Sinica, Taipei, Taiwan, lin@earth.sinica.edu.tw; CHEN, C., National Chung Cheng University, Chia-Yi, Taiwan, seichen@eq.ccu.edu.tw
Deep “non-volcanic” tremor has been observed at many major plate-boundary faults, which provides new information about fault slip behaviors below the seismogenic zone. Several studies have shown that large earthquakes at regional and teleseismic distances can trigger tremor activity. However, it is not clear whether tremor precedes large earthquakes or tremor triggered by distant earthquakes leads to other local earthquakes. Here we conducted a systematic analysis of tremor activity beneath the southern Central Range of Taiwan one month before and after the 03/04/2010 M6.4 Jiasian earthquake. The study period is chosen mainly because the hypocenter of the Jiasian event was located at the southwest (~30 km away) of the triggered tremor sources identified from our previous studies. In addition, the 02/27/2010 Mw8.8 Chile earthquake occurred a few days before the Jiasian event, providing a unique dataset to better understand the relationship between tremor activities and large earthquakes. We computed envelope functions from the 2-8 Hz band-passed-filter data recorded by short-period and broadband stations. We used standard envelope cross-correlation technique to auto-detect and locate tremor and visually confirm the results as bursts of high-frequency, non-impulsive seismic energy that are coherent among many nearby stations. The preliminary tremor locations are scattered around the region where triggered tremors are located. In addition, we examined triggered tremors during the surface waves of the Chile earthquake. Although the dynamic stress from the Chilean event is higher than the tremor-triggering threshold of ~9 kPa in Taiwan, this event did not trigger tremor. However, we do find a moderate increase of tremor activity ~1 day after the Chile mainshock, and long after the Jiasian earthquake. In our next steps, we will refine our tremor detection and locations, and then quantify the relationship among the tremor, the Jiasian main shock, and distant earthquake.
Session:Guide to Sustainable Seismographic Networks
Presenter   Kim, Won-Young
Schedule   Fri PM / Poster
Room   Ballroom B
Deployment of a Seismographic Network in Bangladesh: Fostering a Seismological Community through Training and Facility Development
KIM, W. Y., Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, wykim@ldeo.columbia.edu; AKHTER, S. H., Department of Geology, University of Dhaka, Dhaka, Bangladesh, shakhter@univdhaka.edu; SEEBER, L., Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, nano@ldeo.columbia.edu; STECKLER, M. S., Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, steckler@ldeo.columbia.edu
There is a lack of seismological capacity in Bangladesh for a country with a significant earthquake hazard. Small to moderate earthquakes are not uncommon, and the country has a history of large historical earthquakes. Most notable are the M8.7 Great Indian Earthquake of 1897 and the M7.5? Arakan earthquake of 1762, which affected the northern and southeastern parts of the country. Despite this, and the hazard from a possible seismic gap on the eastern side of Bangladesh, there are no fully trained seismologists in the country. We established an initial seismic station at Dhaka University in 2003 and since 2007 have expanded it to a permanent network that includes stations at five other universities and a temporary portable network. The permanent Bangladesh University Seismic Network (BUSN) utilizes surplus dataloggers donated by the IRIS/PASSCAL program and the Earthworm seismic data acquisition and processing software developed and supported by the U.S. Advanced National Seismic System (ANSS). We adopted a strategy to make the seismic data acquisition in real time via the Internet together with co-located GPS geodetic system for long-term stability and sustainable operation. At this stage only a few people have received significant seismological training in the operation of the equipment and analysis of the data. The scientists at the other universities in Rajshahi, Khulna, Patuakhali, Sylhet and Chittagong cannot use the network data to locate or study the earthquakes they help record, even if they had the training to do so. They are therefore currently limited in using the data for teaching or research, despite an interest in doing so. Thus we plan a mixture of starting a basic training program and developing a long-term training facility at Dhaka University through the USAID support. The US scientists who will provide the training will be supported by the PIRE grants from NSF.
Session:New Madrid Seismic Zone: Our Understanding on the 200th Anniversary of the New Madrid Earthquake Sequence
Presenter   Pratt, Thomas
Schedule   Wed 3:00 PM / Oral
Room   Ballroom C
Kinematics of the New Madrid Seismic Zone, Central U.S., Based on Analog Stepover Models
PRATT, T. L., U. s. Geological Survey, Seattle, WA, tpratt@ocean.washington.edu
Simple, three-fault stepover models have been proposed to explain the unique pattern of earthquakes in the New Madrid Seismic Zone (NMSZ) of the central United States, with the northwest-trending Reelfoot thrust fault transferring slip between two northeast-trending strike-slip faults. However, these simple models fail to explain the presence or orientation of several faults and seismicity lineations. Analog sandbox models of stepover structures produce a far more complex fault pattern than those proposed for the NMSZ. Comparison of the NMSZ with one