Initial Results at Reducing Systematic Errors for Seismic Event Locations Using a Model Incorporating Anisotropic Regional Structures

摘要

We are utilizing a mapping of the lateral and anisotropic variations in Pn velocities beneath continents across the globe (Smith and Ekstrom, 1999) to predict travel times of P-wave propagation at distances of 2-14 degrees. At such distances the phase Pn is the seismic phase that is most frequently reported and that thus controls the location accuracy. This is important in CTBT applications as many events of interest are only detected at these distances. We are thus working on reducing the systematic errors in Pn travel- times and the resulting seismic event location at regional distances using our mapping. In our investigations we have begun by establishing a list of ground truth events by which to test locations using our different models. In establishing this list we have endeavored to include a variety of geographic areas and sizes of events. We have also developed a grid-search algorithm to relocate each of these events using isotropic, laterally varying, and full anisotropic models. In our initial studies we have not accounted for raypath effects which may prove to be significant. Our results from the first stage of this study indicate a progressive improvement in the relocation with increased model complexity. However, significant systematic errors remain in locations where heterogenity is accounted for but anisotropy is not. The most significant results appear to be for events with few stations reporting but with reasonable azimuthal distribution.