Seismic velocity structure of the Puget Sound Region from three dimensional nonlinear tomography

In this dissertation I describe a non-linear seismic tomography experiment in the Greater Puget Sound Region (GPSR). The GPSR contains portions of three distinct geologic provinces: (1){A0}the Coast Range Province---composed of the Olympic Mountains and the Siletzia terrane lying along the Washington Coast (the western edge of the GPSR). (2){A0}The Puget Lowland---an approximately linear depression that stretches from Oregon's Willamette Valley to the Strait of Georgia in Canada. The Puget Lowland lies in the middle of the GPSR. (3) The Cascade Range---lying along the eastern edge of the GPSR and characterized by extensive episodic volcanism since the later Mesozoic.; The result of this study is a three-dimensional model of the P-wave velocity within the GPSR. Interpretation of this model provides information about the subsurface geology in the region. The method used to perform the tomography has been developed as part of this research. The method uses a finite-difference algorithm to calculate seismic travel-times to every point in the region using the full 3-d velocity model. The method is capable of using three different types of data: (1){A0}earthquakes with unknown hypocenters. The earthquake hypocenters are found as part of the model during solution of the tomography problem. (2){A0}Explosions or other seismic events with known locations. (3) External data constraining the seismic velocity at known locations within the model.; There is a good correlation between the velocity model derived in this experiment and several known geologic structures in the GPSR, including: the core of the Olympic Mountains; high seismic velocity where the basalt that makes up the Siletzia terrane outcrops; and low-velocity regions at basins under the cities of Seattle, Tacoma, Everett, and Chehalis. The data provides sufficient resolution to delineate the geometry of the contacts between these units within a large portion of the GPSR.