Title

Regional characterization of the seismic wave propagation of central Eurasia using deterministic crustal models

Date of Completion

January 1997

Keywords

Geophysics

Degree

Ph.D.

Abstract

This study investigates the effects of large and small scale 3-D heterogeneities on the efficiency of regional seismic waves using deterministic models of crustal structure. Dynamic ray tracing is used to investigate effects on regional wave propagation due to large scale variations in the crustal thickness and shallow sediments. Ray tracing results are compared to amplitude ratio studies and regional data from three different arrays in central Eurasia. The effect of the large scale variations in crustal and basin thickness on Lg wave propagation are predicted. The method of locked modes implemented with the Born approximation for single scattering is developed and used to determine the effect on Lg coda of small scale heterogeneities in both the lateral and vertical direction. The mode-Born method is used to model regional data using arbitrary placement of scatterers. Regional array data from Pinon Flats, CA, which exhibits off azimuth arrivals from local faults, is compared to synthetic seismograms synthesized from a fault structure using the Born-locked-mode method.^ The location and scale lengths of the crustal heterogeneities that are important to the scattering of regional seismic waves, and thus the shape and amplitude of Lg phase and Lg coda, are determined at both the large and small scale. Ray tracing predicts large scale effects of blockage and focussing of Lg, where as the mode-Born scattering due to small scale heterogeneities predicts the complexity, shape, and length of the coda that is observed in regional data. The programs developed for this research enable the rapid calculation and prediction of the efficiency of regional Lg propagation in an arbitrary region of the world given only a crude model of crustal and basin thickness and a regional 1-D velocity model. ^