Determination of lateral heterogeneity in surface wave velocity using a two-dimensional Fourier analysis method with applications to the basin and range

Based on harmonic analysis, a new surface wave inversion method, the 2-D Fourier coefficient method, is developed and implemented in this thesis to study regional surface wave velocity lateral heterogeneities. If there exists a well-distributed path coverage and if appropriate approaches for improving resolution, such as eigenvalue truncation and coordinate rotation are used, then a reasonable surface wave inversion model can be reconstructed. This method represents a new approach to seismic tomography for regional areas of interest.; The results obtained using this method are comparable to or better than those obtained using the block-boundary regionalization method based on analysis of synthetic examples. When one has little knowledge of the earth structure, especially the location of velocity boundaries, this method is superior to the block-boundary regionalization method. To understand the resolving power that the data possess, the Backus-Gilbert theory was employed to analyze resolving power for both synthetic and real data studies.; This new method is then applied to observed surface wave phase velocity data to study lateral heterogeneity in the Basin and Range Province and its adjacent geological regions in the western United States. These limited data can only allow harmonic analysis up to a degree of 2 and a resolvable wavelength of approximately 500 km. The resulting Rayleigh and Love wave velocities show significant surface wave velocity lateral variations with respect to the region's average velocity model. The results are also consistent with these of Patton (1989, personal communication) using a pure-path regionalization method employing a block-province grid. The phase velocity anomalies found in this study generally correlate negatively with crustal thickness and Pn velocity; crustal thickness appears to be the most important factor in controlling the phase velocity anomalies.