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SURFING THE INTERNET FOR STRONG MOTION DATA

  • INTRODUCTION

    Earthquake strong motion data are useful for a wide array of seismological and engineering research and applications. Unfortunately, strong motion data has never been easy to acquire. Data are available from a diverse array of organizations and services, and 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 remote collection of strong motion data easier; what has not changed is the fact that many organizations collect strong motion data, and few have direct approaches for providing the data to other users. Although I am not directly associated with any data source, I presently receive at least 5 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. As you can see, it is to my benefit to provide the information below, and hence, I created this web page (column) on the subject. (Since space is limited, a more extensive version of this summary can be found online at http://www-socal.wr.usgs.gov/smdata.html.)

    While the purpose of this web page is to provide information on online resources, for completeness sake, I include other means for acquiring data and information since it seems to be lacking elsewhere. Accessing weak motion data is not addressed here and I apologize in advance for any omissions or inaccuracies. Please address corrections or updates to me directly (wald@usgs.gov), 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.

  • TYPES OF DATA RESOURCES

    I classify strong motion resources into three categories:

    DATABASES

    (true relational databases)
    DATA SOURCES AND/OR ARCHIVES
    (data collection agencies, or archived single- and multi-agency collections)
    PRODUCTS AND INFORMATION
    (ground motion maps, slip models, etc.)

  • DATA ACCESS AND FORMATS

    So, how does 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, the DATABASES are particularly useful for choosing an accelerogram within a given set of parameters, say all stations within 10 km of a magnitude 6-to-7 earthquake. However, this flexibility also requires some investment in time: getting a user account, downloading the users' manual, and learning at least the basic tools for manipulating the database.

    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 choosing what you see in front of you. There is no way to choose subsets of data based on selected 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 (see information on contacts under CDMG, NGDC, and LDGO).

    A further (unfortunate) reality is that at this time there is no standard format for ground motion data. There are nearly as many data formats for strong motion data as there are data sources: Try SAC, SMC, Volume 1, 2 and 3, SEED, numerous ASCII, *.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) and the University of Southern California (USC), I will briefly mention these formats below. There is a program "V2S" in the USGS BAP software (see USGS Web site) for DOS that translates CDMG, USC, Caltech and a few other formats into USGS SMC format.

    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, velocity, and displacement). 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 web 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, velocity and displacement) 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.



    ACKNOWLEDGMENTS

     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/).



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    This page is <URL:http://www-socal.wr.usgs.gov/smdata.html/>
    Created and Maintained by David Wald (U.S.G.S) (wald@usgs.gov)
    Last modified 4.29.97 (djw). General Disclaimer .