ADVANCEMENT IN-SOURCE ESTIMATION TECHNIQUES USING BROAD-BAND REGIONALSEISMOGRAMS

One important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases (such as P nl/surface wave, SV/SH). Because the misfit errors used in some wavefo rm inversions are normalized by the data and synthetics, the amplitude information in the data has not been fully utilized. In this article, we modify the ''cut and paste'' source estimation technique (Zhao and Helmberger, 1994) by removing this type of normalization. It is shown that the modified method increases the stability and resolution of in version. When multiple stations at different distance ranges are used, a distance scaling factor is introduced to compensate for the amplitu de decay with distance. By applying the technique to the TERRAscope da ta, we have determined source mechanisms and depths of 335 southern Ca lifornian events with M(L) greater than or equal to 3.5. The amplitude decays with distance are r(1.13) for Pnl, r(0.55) for Love waves, and r(0.74) for Rayleigh waves. In contrast to generally shallow source d epths reported by the southern California short-period network, the de pth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km.