Application of P-Wave Spectral Measurements to Short-Period Discrimination
TEXAS INSTRUMENTS INC DALLAS EQUIPMENT GROUP
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A method was developed for computing the displacement spectrum of earthquake dislocations and presumed explosions with greater accuracy. Measurements of corner frequencies and displacement amplitudes are considerably less ambiguous than those derived from conventional spectra. The relatively narrowband system response is apparently correctly accounted for in the equations for ground displacement, so that the displacement spectra are in principal valid up to 10 Hz. Presently, roundoff errors compounded by estimation errors due to the coda of the events limit the accuracy and validity of spectra at low frequencies less than approximately 1 Hz. It is anticipated that with further development of the method, valid displacement spectra can be measured at lower frequencies. Discriminants between earthquakes and explosions were derived from measurements of corner frequency and displacement amplitudes taken from the spectra of events. These discriminants appeared to be at least as effective as other short-period spectral discriminants such as spectral splitting, spectral moments, and spectral magnitudes. The discriminants utilized measurements of spectra which are accurate only at frequencies greater than 1 Hz. Addtional discriminants based on low frequency characteristics of the displacement spectra may be possible in the future when the accuracy of displacement spectral calculation is improved.
- Seismic Detection and Detectors