Multi-Resolution Global Models for Teleseismic and Regional Event Location

摘要

Reconciliation of structures shown in global models of Earth structure with those shown in detailed, high-resolution regional models has become one of the most important tasks in seismic tomography. Recent studies have shown that combination of regional seismic phases with teleseismic phases can greatly increase location accuracy; however, for this to be the case, the velocity structure has to be well resolved on a fine scale. The most efficient method to accomplish this task is development of multi-resolution models using local (but smooth) basis functions that increase in resolution from regions with sparse data coverage to regions of dense coverage. This paper reports on recent results from an ongoing project designed to bridge the gap between regional and global seismic tomography and achieve correspondingly incremental improvements in event location. We have previously developed a moderately high- resolution global model (equivalent to spherical harmonic degree 18) using local spline functions. This model improves locations using teleseismic phases over other more finely parameterized models ( Antolik et al., 2001). Here we extend the same techniques to simultaneous development of more detailed regional models for inclusion within the global model. We describe progress in constructing a new regional model of the Africa/Mediterranean region which makes use of surface wave dispersion data, regional travel times and waveforms, and teleseismic phase arrivals. This model also incorporates shear wave anisotropy and agrees well with other published models for the region. Other regions for which we intend to develop combined regional/global models include the former Soviet Union and North America. Tomographic models can also be vastly improved through the use of sources with calibrated travel-time data (i.e., reference events with accurately known locations).