July/August 2002

A Study of Earthquake Science

After an extended period of study, the National Research Council's Committee on the Science of Earthquakes has finally released its report, Living on an Active Earth: Perspectives on Earthquake Science. As the chairman of the committee that produced the report, I hope it will be effective in documenting the marvelous progress made in earthquake research and in helping scientists and their supporting agencies set a vigorous research agenda for the years ahead. I have to admit, however, that digesting this tome-more than 400 pages long and hardly the type of book one hauls to the beach-could be a challenge. So I jumped at the opportunity offered by the SRL editor to summarize some aspects of the report and salt in a few personal perspectives.

The NRC study was motivated by questions surrounding the effectiveness of the "knowledge based" strategy taken by the National Earthquake Hazard Reduction Program (NEHRP), the mainstay of federal earthquake research since 1977. A series of critiques in the early to mid-1990's, including a 1995 report by the congressional Office of Technology Assessment titled Reducing Earthquake Losses, concluded that the NEHRP approach short-changed practical measures for mitigating earthquake losses, creating an "implementation gap" in which risk-reduction efforts lagged far behind the knowledge base created by basic research. I was chairman of the NRC Committee on Seismology at the time, and it seemed to us that, while everyone could get behind a more vigorous program to implement research, the implication that the $100 million per year allocated to NEHRP--a small budget for a vast problem--would be better spent on short-term mitigation efforts was misguided. Missing from the NEHRP debate was an appreciation of the outstanding prospects for, and potential payoffs from, long-term basic research. We thus submitted a proposal to the National Academy of Science and received a sizable grant from its Arthur L. Day Fund to "prepare a comprehensive summary of the multidisciplinary research throughout the earth and physical sciences on the origins, properties, and consequences of earthquakes, assess the research goals for the field of earthquake science, particularly as they support engineering and policy efforts to improve seismic mitigation strategies, and identify strategies to improve the communication of earthquake science to engineers, policy makers, and the general public." A Committee on the Science of Earthquakes was duly constituted by the NRC to conduct the study. (The other committee members were Gregory Beroza, C. Allin Cornell, C. B. Crouse, James Dieterich, Arthur Frankel, David D. Jackson, Arch Johnston, Hiroo Kanamori, James S. Langer, Marcia K. McNutt, James R. Rice, Barbara A. Romanowicz, Kerry Sieh, and Paul G. Somerville.)

In its report, the committee has attempted to articulate the rationale for earthquake research from four complementary perspectives: (1) the need to improve seismic safety and performance of the built environment, especially in highly exposed urban areas; (2) the requirements for disseminating information rapidly during earthquake crises; (3) the opportunities for exciting basic science, particularly in the context of current research on complex natural systems; and (4) the responsibility for educating people at all levels of society about the causes and effects of earthquakes. The study comprised five elements, each presented as a separate chapter of the report:

  • Survey of earthquake science from ancient times to the present day, with a discussion of lessons drawn from past research.
  • Evaluation of the current status of seismic hazard analysis and its connections to earthquake engineering, loss estimation, and risk mitigation.
  • Examination of the new technologies in the main observational disciplines of seismology, geodesy, geology, and rock mechanics.
  • Technical assessment of the key issues for future earthquake science, including the application of a dynamic systems approach to integrate observations.
  • Analysis of research opportunities and requirements.

The rise of earthquake science proved to be a fascinating topic, and I was personally struck by how much the deep interplay among geology, physics, and engineering has elucidated earthquake processes and effects. During most of the last century, researchers tended to separate themselves into two distinct communities, one focused on earthquake complexity and how it arises from the brittle response of the lithosphere to deep-seated forces, and another on the forecasting of earthquakes and their site-specific effects. Investigations of the first problem began with attempts to place earthquake occurrence in a global framework and contributed to the discovery of plate tectonics, while work on the second addressed the needs of earthquake engineering and led to the development of seismic hazard analysis. The committee noted how the historical separation between these two lines of inquiry has been narrowed by recent progress on dynamic modeling of earthquake occurrence and strong ground motion. This research has transformed the field from a haphazard collection of disciplinary activities into a more coordinated system-level science that seeks to describe seismic activity not just in terms of individual events but as an evolutionary process involving dynamic interactions within networks of interconnected faults. Not surprisingly, the bright prospects for this kind of "earthquake system science" emerged as a major theme of the report.

Our historical survey reviewed how much has been learned from coordinated interdisciplinary investigations in the aftermath of large earthquakes, beginning with the publication of The Great Earthquake in Japan, 1891 by the Seismological Society of Japan and the seminal work on the 1906 San Francisco earthquake by the Lawson Commission and continuing with the rich postevent studies of Landers, Northridge, Kobe, and Hector Mine. The lesson here is that the scientific community must be well organized to take advantage of widely felt earthquakes, which create opportunities for new research, effective education, and major funding. In fact, while the publication of Living on an Active Earth is not likely to cause much of a stir inside the Beltway--unlike most NRC studies, it was not requested by any federal agency--its time will come when the government is pressed into action after the next big one.

Experience also makes clear the importance of standardized instrumental data, synoptic observations, and geologic field work. The report documented the impressive degree to which research has been accelerated through the development of new technologies. The long list includes networks of broadband seismometers and GPS receivers, InSAR systems for imaging ground deformations, high-precision geochronologic methods for neotectonic and paleoseismic studies, and laboratory apparatus for investigating fault friction. Using high-performance computing and communications, scientists now have the means to process massive streams of observations in real time and, through numerical simulation, to quantify the many aspects of earthquake physics that have been resistant to standard analysis. We can expect a lot of new information about earthquake processes to come from these observational systems, and we are now in a better position to capitalize on this information in understanding active fault systems on time scales of days to centuries for the purpose of improving earthquake forecasting, and fault ruptures on time scales of seconds to minutes for the purpose of predicting strong ground motions.

Despite these successes, many scientific questions about earthquakes remain to be answered. No theory adequately describes the dynamic interactions among faults or the basic features of rupture nucleation, propagation, and arrest. The report identified specific long-term goals in eight areas of interdisciplinary research that offer exceptional opportunities to further the national effort in earthquake science:

  • Fault Characterization: Document the locations, slip rates, and earthquake history of dangerous faults throughout the United States.
  • Global Earthquake Forecasting: Forecast earthquakes on a global basis by specifying accurately the probability of earthquake occurrence as a function of location, time, and magnitude, as well as the magnitude limits and other characteristics of likely earthquakes in a given place.
  • Fault-system Dynamics: Understand the kinematics and dynamics of active fault systems on interseismic time scales and apply this understanding in constructing probabilities of earthquake occurrence, including time-dependent earthquake forecasting.
  • Fault-zone Processes: Characterize the three-dimensional material properties of fault systems and their response to deformation through a combination of laboratory measurement, high-resolution structural studies, and in situ sampling and experimentation.
  • Earthquake Source Physics: Understand the physics of earthquake nucleation, propagation, and arrest in realistic fault systems, and the generation of strong ground motions by fault rupture.
  • Ground-motion Prediction: Predict the strong ground motions caused by earthquakes and the nonlinear responses of surface layers to these motions, including fault rupture, landsliding, and liquefaction, with enough spatial and temporal detail to assess seismic risk accurately.
  • Seismic Information Systems: Develop reliable seismic information systems capable of providing (a) time-critical information about earthquakes needed for rapid alert and assessment of impact, including strong-motion maps and damage estimates, and (b) early warning of impending strong ground motions and tsunamis outside the epicentral zones of major earthquakes.
  • Partnership for Public Education and Outreach: Collaborate with earthquake engineers to educate emergency-response officials, government authorities, commercial interests, and the general public about the nature of earthquake hazards and the proper use of earthquake information.

The prospects for earthquake science are well illustrated by the vexing issue of earthquake predictability. On short time scales (hours to days), no method for event-specific earthquake prediction has yet demonstrated skill at a statistically reliable level; indeed, the chaotic nature of brittle deformation may imply that useful short-term prediction cannot be achieved, even with substantial improvements in the ability to detect precursory signals. Near-field observations before and during large earthquakes are too few and too limited, however, to rule out categorically the feasibility of short-term earthquake prediction. For example, we do not understand the interplay between major earthquakes in subduction zones and the "silent earthquakes" recently observed in these zones by geodetic networks in Japan and Cascadia. Moreover, there are both observational and theoretical reasons to believe that large-scale failures within some fault systems may be predictable on intermediate time scales (years to decades), provided that adequate knowledge about the history and present states of the systems can be obtained. It is not yet clear whether probabilistic forecasting methods can be devised that take advantage of this potential predictability, but such methods could contribute significantly to the reduction of earthquake losses. Fundamental understanding of earthquake predictability will likely come through a broad research program with the goals of improving knowledge of fault-zone processes; the nucleation, propagation, and arrest of fault ruptures; and stress interactions within fault networks.

Substantial investments will have to be made in order to realize the scientific goals outlined in the report. The committee catalogued the research requirements in the key observational disciplines of seismology, geodesy, geology, and rock mechanics, as well as the integrative, multidisciplinary studies needed to gain a comprehensive understanding of earthquake phenomena. It argued that the transition of earthquake science to a systems-oriented, physics-based approach has important ramifications for the types of cooperative research activities and organizational structures that will be most effective in addressing the outstanding research problems, both basic and applied. For example, multi-institutional research centers and distributed collaboratories with advanced information-technology infrastructures will play a larger role in coordinating research and synthesizing results into system-level models of earthquake behavior. Such organizational structures will provide new capabilities for disseminating earthquake information and research results, formulating science-based strategies for loss reduction, and educating groups at all levels about the role of science in disaster mitigation and loss reduction.

The committee concluded that the technological investments and programmatic support required for earthquake research during the next ten years will outstrip the resources currently available through NEHRP and other federal programs. Major initiatives by the two NEHRP science agencies illustrate this situation. The USGS has proposed the deployment of an Advanced National Seismic System (ANSS), which would improve the U.S. National Seismographic Network, modernize regional networks, and set up 6,000 strong-motion stations in high-risk urban areas. A fully implemented ANSS would upgrade regional networks to modern seismic information systems and provide the framework for developing real-time warning systems. The ANSS plan, if brought into full operation, would greatly enhance seismological instrumentation in the United States and would contribute substantially to the objectives outlined in our report. This system will require capital investments of approximately $170 million, and its annual operational costs are estimated to be about $47 million. In comparison, the congressional appropriation for the entire USGS component of NEHRP budget was only about $50 million in FY 2001.

The second example is the EarthScope Project, proposed by the National Science Foundation in conjunction with NASA and the USGS. This facility-oriented program includes the Plate Boundary Observatory (PBO), which would expand existing geodetic networks with additional permanent GPS stations and campaign-style observations and fill major gaps in measurements of plate-boundary deformation in the western United States. The second geodetic component--a satellite-based InSAR imaging system--would map decimeter-level deformations of fault ruptures continuously over areas tens to hundreds of kilometers wide, as well as a range of nonseismic phenomena such as volcano inflation, glacial flow, and ground subsidence. USArray, the seismological component of EarthScope, would map lithospheric structure nationwide on scales of tens of kilometers and provide new capabilities for active-source imaging of specific features, including sedimentary basins where seismic risk is often high. EarthScope would also construct a San Andreas Fault Observatory at Depth (SAFOD) that would for the first time sample the fault by deep drilling, monitor its seismicity and strain, and perform in situ experiments to depths of 4 kilometers. Deployment costs for the EarthScope instrumental systems are estimated to be $91.3 million for PBO, $245 million for InSAR, $64 million for USArray, and $17.4 million for SAFOD. Data analysis and management will require an additional $15 million to $20 million per year during the first decade of EarthScope operations. In comparison, the total FY 2001 geoscience expenditures by the NSF in support of NEHRP were about $12 million.

Geologic field work will be an important part of EarthScope; yet, even if the NSF initiative were fully funded, it would not boost resources for earthquake geology to the levels envisaged in our report. The research opportunities for characterizing the structure and history of active fault systems warrant a severalfold increase in the neotectonic and paleoseismic studies currently supported by the USGS and NSF. Work in this area is limited by the small number of earthquake geologists engaged in this type of research, underlining the need for increasing efforts in geoscience education at both the undergraduate and graduate levels.

The experience gained during NEHRP demonstrates that the willingness of society to invest in risk reduction is best achieved through an active collaboration among scientists, engineers, government officials, and business leaders, working together with an informed populace. A corollary is that earthquake research will contribute to risk reduction more effectively when it is carried out in a context that recognizes the problem's engineering, economic, and political dimensions. The report pointed out that no agency is responsible for ensuring an integrated approach to research problems in earthquake science and engineering, and better mechanisms should be developed for bringing the two fields together to exploit potential synergies. Cooperation among the NSF and USGS earthquake science centers and the NSF earthquake engineering centers will be critical to this goal, as will science participation in engineering programs such as the Network for Earthquake Engineering Simulation (NEES).

The basic message in Living on an Active Earth is that research to understand earthquakes and their effects will be central in any plausible strategy for decreasing earthquake risk. The technological and conceptual developments have positioned the field of earthquake science for major advances, and investments made now will eventually pay off in terms of saved lives and reduced damage. These returns can be realized sooner by encouraging unconventional lines of research, coordinating scientific activities across disciplines and organizations (especially between scientists and engineers), and supporting international programs to investigate the global diversity of earthquake behavior. Few problems are more challenging to science or strategically relevant to the nation, and few have a greater potential for elucidating the fundamental geological processes that shape the face of the planet.

I'm much too close to this study to assess with any degree of objectivity how well the committee accomplished its task of assessing the status and prospects of earthquake science or whether the vision offered in the report is adequate. However, writing this document provided the committee with a fine education in the achievements and excitement of the science, and I hope our efforts will help to convince young scientists to pursue earthquake research with the energy it deserves.

Thomas H. Jordan
Director, Southern California Earthquake Center
University of Southern California
Los Angeles, CA 90089-0742, USA

To send a letter to the editor regarding this opinion or to write your own opinion, contact the SRL editor by e-mail.

Posted: 4 December 2002