Focal mechanisms and seismic anisotropy analysis of local earthquakes at the Cove Fort-Sulphurdale geothermal site, United States.

Cove Fort-Sulphurdale is located in central-western Utah, which is characterized by its unique geologic features and rich geothermal resources. For better development of geothermal reservoirs, it is necessary to have the know-ledge of stress and fracture distribution of the region. Based on the previous work, we use the waveform matching method to invert the focal mechanisms of local earthquakes collected in Cove Fort-Sulphurdale, constrained by first arrival P wave polarities and S/P amplitude ratios. Furthermore, we also use the shear wave splitting analysis method to study the anisotropy in this region. Combining both focal mechanism and anisotropy results, we can determine the stress distribution and fault/fracture directions. The results show that the waveforms of synthetic data match real data very well, and the first arrival P wave polarities and S/P amplitude ratios are close. Fault plane solutions have strikes trending in approximately N-S direction, which is consistent with the maximum horizontal principle stress indicated by the stress map of America and our current understanding of the tectonics in this region. Shear wave-splitting analysis results also show that if the anisotropy is mainly caused by the fault structure in this region, the strikes of the main faults/fractures should be in the N--S direction.