Seismic tomography and synthetic calculation in Coso geothermal area, Inyo County, California

In this study, inverse and forward methods have been developed to map and model distributions of attenuation, velocity, anisotropy and cracks. Tomographic methods were used for inverse problems and the pseudospectral method was further improved for forward problems. The developed tomographic methods were applied to Coso geothermal field, California, and high resolution, three-dimensional models of attenuation, P- and S-wave velocities, Poisson's ratio, porosity and anisotropy were obtained.; Pulse widths were used in a tomographic inversion for attenuation structures. A high attenuation channel was identified at the southwestern tip of the geothermal field and is probably a fossil magmatic conduit. Numerical modeling with a pseudospectral method was performed to investigate the applicability of the inversion scheme to fractured regions. A linear relationship between pulse broadening and traveltime was confirmed.; Traveltimes for microearthquakes were used in a non-linear inversion to derive three-dimensional P- and S-wave velocity models. The models were further used to map distributions of Poisson's ratio and porosity, as represented by perturbations of {dollar}Vsb{lcub}p{rcub}{dollar}/{dollar}Vsb{lcub}s{rcub}{dollar}, ratio and {dollar}Vsb{lcub}p{rcub} cdot Vsb{lcub}s{rcub}{dollar} product, respectively. Poisson's ratio at Coso ranged from 0.15 to 0.35 with an average of 0.224, which is significantly lower than the crustal average of 0.25. High Poisson's ratios were more extensive at shallow depths ({dollar}<{dollar}1.5 km) and lower Poisson's ratios at greater depths (1.5-3.0 km). A magma intrusion model for the last major magmatism in the Coso region was proposed.; To map the distribution of anisotropy, seismic velocity was represented by a Cartesian tensor and new inversion methods for traveltime data were developed. The velocity representation was formally derived from a Taylor series expansion of a smoothly extended velocity function. The conventional isotropic traveltime tomography was a special case of this inversion scheme. The method was applied at Coso and the resultant anisotropy distribution was consistent with the proposed magmatic intrusion model. Deviatoric stress was estimated to be 3-6 MPa at geothermal production depths (1-2 km) and residual crack density ranged from 0.0078 to 0.041.; To use the tomographic models for waveform simulation, pseudospectral methods were developed to propagate waves in three-dimensional media. The pseudospectral method was extended to account for anisotropy, attenuation and cracks. New methods for calculating boundary conditions at the free surface and along absorbing boundaries of a finite grid were developed and tested. A finite, twice differentiable reduction function which achieved a 99% reduction of incident waves over 3 wavelengths was proposed. In the context of pseudospectral wave propagation, this implies a boundary layer of at least 6 grid nodes.