Determination of source parameters at regional distances with three‐component sparse network data

Abstract

We find remarkable similarities between regional body waves recorded by the TERRAscope network of broadband stations and synthetics constructed 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 the 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, only the three‐component records of a single station are required because the ratio of SV to SH energy is dependent upon source orientation. Sensitivity analyses examining the effects of source mislocations and velocity model on the inversion results show that the long‐period body waves appear relatively insensitive to lateral mislocations but are sensitive 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, (Mw = 5.2) Lee Vining and the December 3, 1991, (Mw = 5.1) Baja California events are used to demonstrate the effectiveness of the inversion method. For the Baja event, we obtained unique results using a single station. For the Lee Vining event, inversions using a single station were not as stable. However, we found that using two stations with only a 24° aperture provided enough constraint to obtain unique results.

Source Description of the 1999 Hector Mine, California, Earthquake, Part I: Wavelet Domain Inversion Theory and Resolution Analysis

“…The simple layered models can model the wavefield reasonably well. The southern California standard model (SoCal: Dreger and Helmberger, 1993), which is used in the automated source inversion for events in this region (Zhu and Helmberger, 1996), seems to be a good choice. The Mojave model (Jones and Helmberger, 1998) was shown to work well in explaining the waveforms from the Landers aftershock sequence, with similar paths for the Hector Mine earthquake, and could be another candidate.…”

“…We fix the rake angles of all asperities to 175Њ, but each asperity has an individual rise time and slip amplitude. (Jones and Helmberger, 1998) and the dashed lines show the Southern California standard model (SoCal; Dreger and Helmberger, 1993). Moreover, the rupture velocities are also varied asperity to asperity. For instance, rupture front speed is only 1.8 km/ sec for the asperity on fault 2.…”

Slip history of the 2003 San Simeon earthquake constrained by combining 1‐Hz GPS, strong motion, and teleseismic data

“…For the observations recorded at stations less than 100 km from the hypocenter, we chose a velocity structure suggested by Walter and Mooney [1982] to generate both static and seismic Green's functions [Xie and Yao, 1989;Zhu, 2003]. The Southern California Crust model (Socal [Dreger and Helmberger, 1993]) was used to generate the waveforms of distant stations. Since there is no surface rupture [Hardebeck et al, 2004], the slip of near-surface subfaults was held fixed at zero.…”

Source Parameters of Moderate and Strong Earthquakes in the Broader Area of Zakynthos Island (W. Greece) From Regional and Teleseismic Digital Recordings

“…Two kinds of regional waveform data are typically used for source estimation, surface waves (Thio & Kanamori 1995) and body waves (Fan et al, 1994;Dreger & Helmberger, 1993). In the present study body waves are used, which are generally less affected by shallow heterogeneities and are more stable than surface waves, although they have a lower signal-to-noise ratio due to their smaller energy.…”