We examine two issues related to the radiation of tectonic earthquake sources: (i) the complexity of the shape of observed source spectra, and (ii) the effect of recording site characteristics on the cut-off frequency fmax of acceleration spectra beyond which spectral amplitudes diminish sharply.
We compute the far-field spectra of the 1979 Imperial Valley and the 1984 Morgan Hill earthquakes from the slip functions that were inferred from detailed inversion studies of strong motion and teleseismic data of these two California strike-slip events. These spectra, along with data from the 1983 Central Japan Sea earthquake sequence (main shock and aftershocks), demonstrate the existence of the so-called patch corner frequency, which is related to the scale-length of heterogeneities of the fault plane. Such a frequency is a distinct feature of the source spectrum of the specific barrier model of Papageorgiou and Aki.
By analyzing accelerograms of the San Fernando earthquake of 1971, we found that fmax determined from records at soil stations is nearly the same as that determined from records at hard rock stations.