Body wave spectra from propagating shear cracks

Abstract

An earthquake source model studied in this paper predicts a higher value of P wave corner frequency than S wave corner frequency; the ratio of P to S wave corner frequency is about 1.3 on the average. This result owes mainly to the slip characteristics on the fault, that is, the center of the fault slips for a longer time than the edges and consequently a greater relative displacement takes place near the center. Relationships of source dimension with the corner frequencies for P and S waves are derived to estimate the source dimension of earthquakes from teleseismic body wave spectra. The far-field spectra from the present model of equidimensional rupture propagation demonstrate the spectral decay of ω-2 at high frequencies. The seismic efficiency is found to be independent of the size of source dimension and expressed as a function of initial stress, stress drop, and rupture velocity. Being interpreted in terms of this model, the ratio of frictional stress to final stress can be estimated from observations of rupture velocity. © 1973, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.