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# Three-Component Borehole Seismometer for Earthquake Seismology

| **Background**The USGS operates extensive networks ofseismic sensors for earthquake hazards studiesand for monitoring man-made explosions.  Thesize of a network, depending upon its purpose,ranges from global to regional and to local. Examples of the application of a local seismicnetwork include the study of aftershockdistribution after a major earthquake and theevaluation of engineering site conditions insedimentary basins.  USGS scientists are alsoworking in partnership with industry to developtechnologies for rapid earthquake notification andresponse that will permit users of these data toavert losses or to guide recovery efforts.  Onetechnology recently developed is a three-component borehole seismometer.
**The Three-Component Borehole Seismometer**Scientists at the U.S. Geological Survey (USGS)have developed a three-component boreholeseismometer with leveling capability for useduring earthquake site response studies.  Thereare several reasons for using such a seismometerin earthquake studies.  For example, the lowvelocity and high attenuation of weathered near-surface rocks strongly influence the amplitudeand phase characteristics of seismic waves.  It istherefore important for earthquake-source andseismic-shear-wave-polarization studies to placeseismometers at depths below the weatheredrocks.  In another example, because surface-wave amplitude decreases exponentially withdepth, the seismic noise generated by humanactivities in a metropolitan area is reducedconsiderably even at a shallow depth.  Thus,borehole seismometers can be used as elements ofa seismic network for determining earthquakelocations and magnitudes.
The USGS three-component boreholeseismometer uses 2-Hz electromagnetic moving-coil geophones as sensing elements.  The systemfeatures a compact internal device for leveling thehorizontal components after emplacement.  TheUSGS three-component borehole seismometerhas a low noise level, consumes no power, issimple to build and is inexpensive.  It is alsosuitable for rapid deployment for after shockstudies and for low-noise operation at remotesites.
**Test Results**The USGS three-component boreholeseismometer has been installed at several sites inCalifornia.  Earthquake data recorded by theborehole seismometers have been used in studieson the effects of near-surface weathered rocks onthe corner frequencies of earthquake spectra nearAnza, CA; on the seismic-shear-wave-polarization characteristics of seismogramsrecorded in the southern California batholith at300 m depth; and on site-resonance amplificationcaused by sedimentary deposits overlyingbedrock in the Marina District of San Francisco.
**For More Information**The USGS is seeking partners tocommercialize this technology.  For moreinformation, please contact the principalresearcher:
Hsi-Ping LiuU.S. Geological SurveyWestern Earthquake Hazards Team345 Middlefield Road, MS 977Menlo Park, CA 94025tel: 650-329-5643fax: 650-329-5163E-mail: liu@usgs.govPrivacy StatementDisclaimerAccessibilityFOIAU.S. Department of the Interior | U.S. Geological Survey              URL: http://www.usgs.gov/tech-transfer/factsheets/FS-231-96.html              Maintainer: Technology Transfer                            Last modified: Thursday, 09-Oct-2003 08:51:43 EDT                            |
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