The Electronic Seismologist has recently been involved with adding strong-motion accelerographs to a regional seismic network. In the process of trying to see how others have done this and, in particular, how others handle strong-motion data and make it available to interested parties, he surfed the Internet looking for what is out there. A few places, such as the USGS strong-motion program and the National Center for Earthquake Engineering Research (NCEER), seem to have lots of data and information about them. The Kyoshin Net in Japan is huge and has lots of data right up to the present. Access to the California Division of Mines and Geology Strong-Motion Instrument Program just changed to a very nice Web page, but its index map is confusing to use. In fact, in each case the techniques for finding out details of the available strong-motion data, reviewing them, or downloading and using them are different, and the interfaces are not always easy or obvious to use for a narrow-minded seismological Web surfer such as the Electronic Seismologist.
Trying to shortcut this wild surfing-safari the "ES" sent e-mail to several people that he knew were experienced in the production or use of strong-motion data, asking for clarification as to what was where and how to get it. Many kind and patient responses were received, most indicating that what he reported being found was a pretty good start, and indeed there was a lot of variability in access techniques, review techniques, data formats, and acquisition procedures. So, it looked like a major surfing expedition complete with multiple Web browsers, careful note-taking, and lots of head scratching was going to be needed.
But wait. One letter was from someone who had started this type of review already and who was experienced at obtaining, integrating, and even using strong-motion data from different sources. Not only that, but with a bit of arm-twisting the ES was able to talk this dude into writing his column for him. The ES guest author this issue is David Wald of the U.S. Geological Survey, who provides his article in an electronic form on the Web at URL http://pasadena.wr.usgs.gov/info/smdata.html. Very much as the "Seismosurfing" document (http://www.geophys.washington.edu/seismosurfing.html) provides an index to organizations providing basic seismological data and information, this work by David might be called "Strongmosurfing", since it provides the same type of information, and then some, for the specialized world of strong-motion seismology.
After reviewing the following summary the weak and timid may decide to forego trying to assemble a comprehensive strong-motion data set from multiple sources. However, we may be able to take heart in an NSF-funded effort called the "US Committee for Advancement of Strong Motion Programs", which I am told by its Chairman, Carl Stepp, will soon be addressing the issue of uniform access and formats for all strong-motion data.
SURFING THE INTERNET FOR STRONG-MOTION DATA
Earthquake strong-motion data are useful for a wide array of seismological and engineering research and applications. Unfortunately, strong-motion data are often difficult to acquire. While they are available from a diverse set of organizations and services, knowing where to look in order to retrieve a particular set of records is, to put it nicely, complicated. This brief summary is intended to provide information on obtaining strong-motion records online (or in other digital form), contacting data sources, retrieving ground-motion parameters, and accessing products and information pertaining to strong ground motions.
The advent of the Internet has certainly made the acquisition of strong-motion data from recording organizations easier. However, there are many such organizations, and few have easy, direct approaches for providing the data to other users. Although I am not directly associated with any data source, I presently receive at least five requests per month for strong-motion data, simply because I have gone through the trouble of assembling collections for individual earthquakes for my own studies. It is to my benefit to provide the information below, and hence I wrote this article on the subject. Since space is limited here, a more extensive version of this summary can be found online at http://pasadena.wr.usgs.gov/info/smdata.html.
While the purpose of this Web page is to provide information on online resources, for the sake of completeness I include other means for acquiring data and information, since this information seems to be lacking elsewhere. I apologize in advance for any omissions or inaccuracies. Please address corrections or updates to me directly (email@example.com), bearing in mind that World Wide Web links often change without notice. These pages will be frequently updated as new sites come online or are modified.
Data Access and Formats
So, how does an engineering research group, a consulting firm, or a high school student for that matter, go about getting strong-motion data for a research project? First off, databases are particularly useful for choosing an accelerogram within a given set of parameters, say all stations within 10 km of a magnitude 6-7 earthquake. However, this flexibility also requires some investment in time and effort that may include getting a user account, downloading the users' manual, and learning at least the basic tools for manipulating the database before getting useful information.
With some of the data sources and archives (e.g., KNET, USGS, CDMG), it is particularly easy to retrieve data, usually sorted by event date, followed by a list of stations, but you are limited to choices based on file names. There is no way to choose subsets of data based on event or site parameters. It is also still possible to get selected digital strong-motion records sent on other media (CD, floppy, tapes) from some of the agencies listed here.
A further (unfortunate) reality is that at this time there is no standard format for strong-motion data. There are nearly as many data formats as there are data sources. I have found the following being used: SAC, SMC, "Volume 1", 2 and 3, SEED, numerous different ASCII formats, and compression or archiving in *.exe, *.zip, etc. Since a large portion of the strong-motion data available is from the U.S. Geological Survey (USGS), the California Division of Mines and Geology (CDMG), or the University of Southern California (USC), I will mention the variability their formats specifically as examples.
The USGS files have .zip suffixes, so on DOS machines use "pkunzip" and with UNIX use the "unzip" utility. The data available from the USGS Web page expands to ASCII Volume 1 data (uncorrected acceleration). The USC files also have .zip suffixes for Volume 1 data; unzipped they expand to Volume 1 ASCII format, but with a different ASCII format than that of USGS. From the CDMG ftp site, files have .exe suffixes which are self-extracting with DOS and can also be extracted with the UNIX "unzip" utility, resulting in ASCII-formatted Volume 2 (corrected acceleration) and Volume 3 (response spectra) files. However, the ASCII format is slightly modified from the ASCII format of USC. Got it? The details of the formats are available from the respective sites.
Types of Data Resources
I classify strong-motion resources into three categories. Under each I list organizations providing information or data, their Web URL's (if there is one), and a very brief description of what can be found. A much more complete description with additional access information can be found through the Web page located at http://pasadena.wr.usgs.gov/info/smdata.html.
There are only a few full relational databases for obtaining strong-motion time histories and parameters and each has its own unique interface and features.
Southern California Earthquake Center (SCEC)
A true relational database is provided here that provides access to parametric (event, station, and accelerogram parameters) and time-series data for earthquakes in southern California (1933-present). There is both an X and Web interface. Time series and station maps can be viewed remotely, and seismograms can be downloaded in SAC or ASCII format with the X version or in ASCII format with the WWW version. The WWW interface is in the final stages of development. Data sources include those from CDMG, USGS, USC, and SCEC. Caveats: SCE, TERRAScope, LADWP data are not included for important earthquakes (Landers and Northridge, for example).
National Center for Earthquake Engineering Research (NCEER)
Both parametric and waveform data can be accessed and downloaded online using "strongmo", an interactive menu-driven program, via the Internet or in dial-up mode. The database contains primarily free-field U.S. and world strong-motion records (up to 1994, pre-Northridge) from the joint LDEO/NCEER/USGS strong-motion digital network as well as USGS, CDMG, and archives from the National Geophysical Data Center (NGDC) and a host of other groups. Caveats: Terminal and dial-up interfaces only now; the Web interface is currently under development.
Center of Geophysical Data Studies and Telematics Applications (CGDS)
This database is part of the European-Mediterranean Seismological Centre (EMSC). In 1996, the CGDS developed a client/server model with a Web interface, and in 1997 scanned photo images of historical strong-motions records were included. Strong-motion recordings of important earthquakes in Asia including the Gazli, Spitak, and Tanshang earthquakes are among the collection.
Data Sources and/or Archives
This section is a list, by region, of organizations which collect data and/or archive their own data. Records can be obtained directly over the Internet or in a variety of formats, including magnetic tapes, floppy disks, CD-ROM, or hard copy. The format of the archives is likely to be a simple table with events listed by dates, followed by station lists.
This large-scale national archive for United States and worldwide earthquake data contains over 15,000 strong-motion records worldwide from 1933 to 1994 and is available on a three CD-ROM collection. An online list of parametric information is available at http://www.ngdc.noaa.gov/seg/hazard/smcat.html.
The USGS provides uncorrected data from the National Strong-Motion Program for recent (1990-1996) earthquakes. Data are from the USGS, Veteran's Affairs, Metropolitan Water District of Southern California, DOE, Army Corps of Engineers, and selected instrumented local structures. There are available accelerograms of historical earthquakes in North and Central America and Hawaii for the years 1933-1986 from a number of agencies.
A new Web page provides a direct online source for CDMG's Strong Motion Instrumentation Program data from most sizable California earthquakes in ASCII-formatted Volume 2 (filtered, corrected acceleration, velocity and displacement) and Volume 3 (response spectra) files.
Northern California Earthquake Data Center (NCEDC), UC Berkeley
NCEDC allows access to strong-motion data from the Berkeley Digital Seismic Network (BDSN) and from the strong-motion borehole stations of the Hayward Fault Network. Broadband Query and Request Form (BREQ_FAST) can be used for information and to obtain data in SEED format.
Southern California Earthquake Center (SCEC), California Institute of Technology
Strong-motion data from CIT/USGS Southern California Seismic Network (SCSN) and TERRAscope stations are archived among other waveform data (short-period and broadband). Acceleration data are available in SAC format.
University of Southern California Earthquake (USC)
USC strong-motion data are available at several other major archive sites and Northridge data is available here by direct ftp.
The K-NET system provides particularly impressive, rapid access to strong-motion data from 1,000 new (1995-96) observatories throughout Japan. Data can be in UNIX, DOS, or ASCII format, depending on request. Internet users can also search the K-NET archives of strong-motion records, site information, and maximum acceleration data, and details about the Kyoshin Net.
A collaborative effort of the Seismological Laboratory, UNR, and the Instituto de Ingeneria, UNAM, the Guerrero Network consists of thirty digital strong-motion accelerographs in Guerrero and neighboring states in Mexico. The Guerrero Strong Motion Network Archive provides acceleration records from 1985 to 1995.
Mexican Strong Motion Database
A CD-ROM is in the making and information should be made available on the World Wide Web.
The Swiss National Strong motion Network has 75 strong motion instruments, including many free-field and dam sites installed over the last five years. On the Web site, there is abundant information about the network and the data recorded to date as well as examples of recorded data.
Friuli Strong-Motion Network, University of Trieste
The Friuli Strong-Motion Network includes ten broadband (with strong motion sensors) stations. Online one can access general network information and station maps, response, and locations. Data available are tabulated, but are not accessible directly through the Internet.
Deprem Arastirma Dairesi (Turkey)
Accelerograms are available for earthquakes recorded on the SMA networks of Turkey since 1976.
Products and Other Information
There are several sources of interesting data or information related to or derived from basic strong-motion data. These can often be considered finished products of interest to end users.
Trinet (USGS, CDMG, CALTECH) rapid interactive ground-motion contour maps and focal mechanism following earthquakes in southern California.
USGS, CDMG, and CALTECH ground-motion parameters are used to generate a rapid (about 3-5 minutes after the event) peak ground-motion contour map and first-motion focal mechanism for significant earthquakes in southern California (M > 4.0). Station locations, peak motion values, and epicentral parameters are also provided in accompanying tables.
A collection of strong-motion maps and finite-fault (slip) source models for California earthquakes.
USGS Pasadena provides a collection of strong-motion maps, strong-motion slip models, and rupture movies via clickable image maps to choose an earthquake and then view different parameters.
NCEER Guide to Obtaining Strong Motion Records
Here there are general references on information about obtaining strong-motion data, recommended relevant publications, and a set of chosen records from several important events, particularly in eastern North America.
CIT Strong Motion Accelerogram Transfer System
SMARTS is a stand-alone "QuickBasic" program to enable users to browse, find, view, and plot various accelerograms from the Caltech and other databases and to compute and plot Fourier and Response Spectra. Recently introduced Inter-story Drift Demand Spectrum can also be computed and plotted.
Thanks to all who provided information used on this page. Some portions of this information were obtained, modified, and updated from NCEER's home page under "obtaining strong-motion records" (http://nceer.eng.buffalo.edu).
SRL encourages guest columnists to contribute to the "Electronic Seismologist." Please contact Steve Malone with your ideas. His e-mail address is firstname.lastname@example.org.
Posted: 6 April 1999