HR: 14:50h
AN: S22D-05    [PDF]
TI: Constraining hypocentral position by focal mechanism and 3D velocity model
AU: * Zhou, H
EM: hzhou@uh.edu
AF: University of Houston, Dept of Geosciences University of Houston, Houston, TX 77204 United States
AB: The quality of earthquake hypocentral position relies on distribution of stations, precision of traveltime picks, and quality of the velocity model. In light of recent advance in improved station coverage, cross-correlation time picking, and more detailed 3D velocity models, I will discuss two approaches to further improve the hypocentral determination. The first is a joint determination of hypocenters with first-motion focal mechanisms. While the hypocentral determination suffers from the tradeoff between focal depth and origin time, focal mechanism solution depends on the hypocentral position but not the origin time. Hence a joint determination of both hypocenter and focal mechanism could improve both solutions. Since the first-motion polarity data is now available at many stations, the joint process is very effective, as shown by tests on over 40,000 earthquakes in southern California. The second approach is a thorough evaluation of the impact of 3D velocity model on the hypocentral determination, particularly in some general scenarios where hypocentral position can be systematically biased by the model error. One such scenario is near the edge of a basin, where the wedge-shaped low velocity basin is difficult to be constrained accurately by most tomographic methods. In this case the location of the basement boundary will greatly impact both lateral and depth positions of the earthquakes. I will present a new deformable-layered tomography method that is effective in constraining the basin boundaries. In general, the 3D velocity model shall be determined together with hypocenters and focal mechanisms of most earthquakes.
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2003 Fall Meeting