HR: 0800h
AN: S21C-0716    [Abstracts]
TI: Propagation of the Near-Field Point Source Finite-Difference Seismograms to Teleseismic Distances Using Propagator Matrices
AU: * Saikia, C K
EM: csaikia@aftac.gov
AF: HQ Air Force Technical Applications Center, AFTAC/TTR 1030 S. Hwy A1A, Patrick AFB, FL 32925, United States
AU: Pitarka, A
EM: arben_pitraka@urscorp.com
AF: URS Corporation, 556 El Dorado Street, Pasadena, CA 91101, United States
AU: Ichinose, G A
EM: gichinose@aftac.gov
AF: MTC Technologies, AFTAC/TT (MTC) 1030 S. Hwy A1A, Patrick AFB, FL 32925,
AB: In this study we present an approach to model teleseismic P waves by interfacing near-field point source seismograms computed using a parallelized finite-difference (FD) algorithm for a localized three-dimensional earth model with the one-dimensional teleseismic seismograms calculated using the propagator-matrix technique. Our finite-difference algorithm includes the effect of topography and treats the free surface as a boundary between two media where the upper medium is represented by the Lame's constants set equal to zero and the lower medium by the established geophysical parameters. The free-surface formulation to handle topography is taken from Pitarka and Irikura (1996) in which the free surface perpendicular to the x axis is set just on the grid points and for the surfaces perpendicular to the z and y directions are set half way between two grid points in the z and y directions, respectively. To propagate the near-source wave field to a teleseismic distance, the point-source FD wavefield is stored on a 2D plane underneath the source and transformed to the ω-p domain using a 2D radon transformation. The transformed F(ω,p) response is filtered using a 2D exponential filter around the desired ray parameter and inverse transformed to the time domain. This filtered wavefield is now a down-going wavefield into the lower structure which is propagated through the remaining part of the source crust followed by a convolution with the t* of the medium and propagation through the receiver crust. The method has proved useful in understanding the effects of the topography and laterally varying crustal layers on the initial part of the P-wave seismograms.
DE: 7203 Body waves
DE: 7219 Seismic monitoring and test-ban treaty verification
SC: Seismology [S]
MN: 2007 Fall Meeting