Calibration of the HGLP seismograph network and centroid-moment tensor analysis of significant earthquakes of 1976

Details Calibration of the HGLP seismograph network and centroid-moment tensor analysis of significant earthquakes of 1976 Calibration of the HGLP seismograph network and centroid-moment tensor analysis of significant earthquakes of 1976

May 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997pepi..101..219e&link_type=abstract

Physics of the Earth and Planetary Interiors, v. 101, p. 219-243.

Physics

8

Scientific paper

A methodology is developed for determining accurate instrument response functions for seismographs of the High-Gain Long-Period (HGLP) Network. Recordings of daily transient calibration pulses provide a detailed history of the time-varying responses of the HGLP stations. When the instrument displacement transfer function is available, knowledge of the seismometer mass, calibration coil constant, and calibration current allows for the prediction of the shape and amplitude of the calibration signal by simple integration of the transfer function. In theory the inverse of this statement is also true, but in practice noise in the recordings contaminates the instrument response function recovered through direct differentiation of the calibration pulse. The unknown transfer function of the seismograph system is, instead, first described by the product of the nominal responses of its mechanical and electromagnetic components. Specific values of the characteristic parameters for each seismograph component are subsequently determined by iterative least-squares minimization of the misfit between observed and model transient calibration pulses. By application of this method to daily calibration pulses recorded on the ten stations of the HGLP network, refined instrument response functions for 1976 and part of 1975 are determined. The results agree well with single frequency amplitude calibration data recovered from station maintenance records, and produce synthetic waveforms which are consistent with data from other well-calibrated stations. We use the recalibrated HGLP data together with long-period data from early International Deployment of Accelerometers (IDA) and Seismic Research Observatory (SRO) digital stations to determine 108 centroid-moment tensor (CMT) solutions for moderate and large earthquakes of 1976. The new CMT results for several major earthquakes, including the Tangshan, Guatemala, and Friuli events, are compared with those of previous studies.

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