DETERMINATION OF SOURCE PARAMETERS AT REGIONAL DISTANCES WITH 3-COMPONENT SPARSE NETWORK DATA

We find remarkable similarities between regional body waves recorded b y the TERRAscope network of broadband stations and synthetics construc ted from a standard southern California velocity model. This model is shown to be effective for a variety of azimuths and ranges throughout southern California. At short periods some of the relative timing of t he body waves are discordant, but at longer periods this becomes less of a factor. Thus we have developed a waveform inversion technique to rapidly determine source parameters using stored Green's functions for events out to 500 km, well outside the TERRAscope network. Often, onl y the three-component records of a single station are required because the ratio of SV to SH energy is dependent upon source orientation. Se nsitivity analyses examining the effects of source mislocations and ve locity model on the inversion results show that the long-period body w aves appear relatively insensitive to lateral mislocations but are sen sitive to source depth. However, the choice of velocity model can be a factor in obtaining reliable estimates of source depth. In this study the October 24, 1990, (M(w) = 5.2) Lee Vining and the December 3, 199 1, (M(w) = 5.1) Baja California events are used to demonstrate the eff ectiveness of the inversion method. For the Baja event, we obtained un ique results using a single station. For the Lee Vining event, inversi ons using a single station were not as stable. However, we found that using two stations with only a 24-degrees aperture provided enough con straint to obtain unique results.