Observation and numerical modeling of seismic wave propagation in both isotropic and anisotropic media

The goal in this Ph.D. research is to constrain lithospheric strain and mantle flow using seismic anisotropy, and to investigate the characteristics of ground motions due to the presence of sedimentary structures. Both seismic observations and numerical modeling have been developed and applied to study a variety of tectonic regimes such as mid-ocean ridges, subduction zones, and sedimentary basins.; The observational studies of seismic anisotropy using shear wave splitting analysis are presented in the first two chapters. Chapter One describes constraints on seismic anisotropy in the North Atlantic using teleseismic S and SS phases. Shear wave splitting analysis shows that anisotropy exists in the North Atlantic upper mantle and may be caused by mantle flow that is not simply coupled to surface plate motions. Chapter Two describes constraints on anisotropy in the eastern Aleutians using local S phases. The observed splitting can be modeled by weak seismic anisotropy in the mantle wedge, and is consistent with compression in the mantle wedge accommodated by arc-parallel or vertical flow.; The last two chapters include the development of numerical modeling of seismic wave propagation in both isotropic and anisotropic media using a 3D fourth order finite difference method. Chapter Three describes ground motion simulations in isotropic basin structures. Amplified and prolonged ground motions as well as body to surface wave conversions are characteristic of sedimentary basins as shown in 3D numerical simulations. Chapter Four describes the development of waveform simulations in anisotropic media and shear wave splitting analysis to model the location, strength and orientation of subduction zone anisotropy. 3D full wavefield modeling shows that shear wave splitting in subduction zones is consistent with seismic anisotropy due to lattice preferred orientation of anisotropic minerals.