HR: 1340h
AN: S53B-1272    [Abstracts]
TI: Analyses and Simulation of 3D Scattering due to Heterogeneous Crustal Structure on Regional Phases; Seismic Source Discrimination
AU: * Pitarka, A
EM: arben pitarka@urscorp.com
AF: URS Corporation, 566 El Dorado St. 2nd Floor, Pasadena, CA 91101, United States
AU: Helmberger, D V
EM: helm@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, MS 252-21, Pasadena, CA 91125, United States
AU: Ni, S
EM: sidao ni@urscorp.com
AF: URS Corporation, 566 El Dorado St. 2nd Floor, Pasadena, CA 91101, United States
AB: The purpose of our study is basic understanding of wave propagation scattering and its effect on regional phases through step-by-step numerical experiments, with the goal of providing useful insights into ongoing research for seismic source discrimination and development of simple empirical models of scattering that can be used in reducing the scatter in measures of Lg and coda wave magnitude. We performed anelastic 3D finite-difference simulations of wave propagation in highly heterogeneous media for a range of receiver distances using double- couple and isotropic explosion point sources. Using a parallelized computer code and models with flat surface topography we have produced synthetic seismograms up to 4.5 Hz at regional distances up to 300 km. Our numerical experiments with 3D velocity models that include random velocity perturbations and small-scale heterogeneities such as microbasins, design to produce wave scattering in the upper 6km of the crust, clearly show that wave-path scattering alone can produce Lg, P and S coda waves with significant energy even for explosion sources. The energy of Lg coda waves depends on the source depth. P/Lg ratios estimated at different frequencies indicate that at high frequencies this ratio could be a good discriminant between explosions and earthquakes. P/Lg ratios below 1Hz are very similar for shallow explosions and deep earthquakes.
DE: 7207 Core (1212, 1213, 8124)
DE: 7219 Seismic monitoring and test-ban treaty verification
SC: Seismology [S]
MN: 2007 Fall Meeting