Coarse-grid finite-difference synthetic-seismogram modeling in heterogeneous elastic media
Abstract
Two classes of discrete-grid methods, the Fourier method and high-order finite-difference methods are tested and applied to two-dimensional (2-D), laterally heterogeneous velocity models of geophysical interest. The Fourier method tested favorably for accuracy and computational efficiency with acoustic wave-propagation problems, although a high-order, staggered-grid, velocity-stress finite-difference method was preferred for elastic models. A modification was made to the finite-difference algorithm for simulating anelastic attenuation (Q$\sp{-1}$) in a velocity model by applying a single-frequency attenuation factor in the computations. The anelastic models allow vertically and lateral variations in Q$\sp{-1}$ as well as compressional and shear velocities. The finite-difference method was applied to a suite of laterally heterogeneous test models to provide a catalog of 2-D seismic propagation effects of structural features in the continental crust and uppermost mantle. The calculations were performed for both a near-surface explosion source and for a teleseismic source simulating an up-going plane, compressional wave. Waveform variations produced by the teleseismic source suggest that lateral velocity variations can strongly influence the character of seismograms which are normally analyzed utilizing a one-dimensional model approximation with the receiver function method. The finite-difference method was also applied to a study of Pg amplitudes in crustal seismology. The results of the study emphasize the utility of Pg amplitudes in reducing the suite of feasible models fitting a seismic data set. The finite-difference method was applied to a data set obtained from the KRISP 90 seismic refraction experiment conducted in Kenya in 1990. The numerical calculations were used to provide amplitude-distance curves of the interpreted velocity model for both Pg and PmP amplitudes for comparison with observed amplitude data. The comparison reveals a close match, particularly for the upper crust (Pg amplitudes) despite the two-dimensional complexity of the Kenya rift, providing support for the velocity model which was previously derived by travel-time analysis.
Degree
Ph.D.
Advisors
Braile, Purdue University.
Subject Area
Geophysics
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