Date of Completion

5-4-2017

Embargo Period

5-4-2017

Keywords

computational seismology, Earth modeling, radiative transport, earthquakes and explosions, wave scattering, Monte Carlo simulations

Major Advisor

Vernon Cormier

Associate Advisor

Richard Jones

Associate Advisor

Michael Fehler

Field of Study

Physics

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

This dissertation presents Radiative3D, a computer code for radiative transport simulations of seismic events, including earthquakes and explosions, in 3-D Earth models, and allowing output of seismogram envelopes from virtual seismometers or information representing bulk energy transport through the model. Radiative transport is an efficient algorithm for Monte-Carlo simulation of high-frequency elastic wavefield energy transport through models featuring both large-scale (larger than wavelength) structure, simulated by deterministic ray tracing, and small-scale structure (wavelength scale and smaller), simulated by a stochastic scattering process. The 3-D models are composed of a collection of adjoining model cells inside of which material properties have simple mathematical description. Within cells, the deterministic mechanism implements curved ray paths in linear gradient background media, and the stochastic mechanism implements pseudo-random preferential scattering based on a formulation that computes mean-free-path and scattering cross sections from a characterization of material heterogeneity in which fluctuation of elastic properties are assumed to follow a von Kármán spectrum of scale lengths. Between cells, material properties may be continuous or discontinuous, in which case reflections and refractions may occur. At the model’s surface, virtual seismometers may be emplaced to record signal channels representative of seismogram envelopes. After introducing the code and theory of operations, two chapters describing initial experiments with the code are presented. In Chapter 4, we present experiments in layered Earth models exploring the effects of variations in the heterogeneity spectrum and their effect on seismic coda generation. In Chapter 5 we present experiments in which crust structure is subject to localized thinning or thickening, simulating graben structures or mountain structures, and analyze their contribution to blockage of the Lg and Pg seismic phases at distant seismometers. We conclude with a roadmap describing the future continued development of Radiative3D.

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