MULTICOMPONENT STRAIN SEISMOGRAPH.
Final rept. 1 Jul 65-31 Dec 67,
GEOTECH GARLAND TX
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A multicomponent system of strain and inertial seismographs has been developed and evaluated at Wichita Mountains Seismic Observatory. The capability of strain and inertial seismographs to operate as matched pairs has been demonstrated. The predicted response of strain seismometers to earth motion is verified by the existence of the proper phase and amplitude relationship and high coherence among selected seismographs for single-source signals. Theoretical values of displacement and differential displacement were computed for several wave types to assist in seismogram interpretation. Investigation of data recorded by vertical strain, crossed strains, and vertical-inertial seismographs shows that the vertical-inertial and strain outputs, when combined through a linear filter, do not provide a significant improvement of the signal-to-noise ratio in the range 0.2 - 10.0 Hz. The application of the azimuthal properties of horizontal strains is examined both in the short-period and long-period pass bands. In the short-period range enhancement of P-waves from near events, and rejection of microseisms is illustrated. Enhancement of long-period surface waves is successfully demonstrated by discriminating between simultaneous arrivals from two epicenters. The identification of SV, and discrimination between longitudinal phases such as pP and PCP is accomplished using strain and inertial seismograms. Strain data from another site was examined and found to behave essentially like that from WMSO. Author