Three-dimensional anatomy of a geothermal field, Coso, southeast-central California

This paper reviews geophysical and seismological imaging in the Coso geothermal field, located in southeast-central California. The Coso geothermal production area covers 6 10 km. Although regional seismicity is addressed, as it sheds light on the magma, or heat, sources in the field, the primary focus of this paper is on the main production area. Three-dimensional inversions for Pand S-wave velocity variations, distribution of attenuation, and anisotropy are presented side-by-side so that anomalies can be compared spatially in a direct manner. Velocity inversions for P and S waves are combined for direct determination of Poisson’s ratio and indirect estimation of variations of porosity in the field. Anomalies southeast of Sugarloaf Mountain are prominent on nearly all analyses. The anomalies coincide with high levels of seismicity and with stress anomalies as determined from earthquake focal mechanism analysis and seismic anisotropy distribution. The anomalies also correlate with high heat flow in the field and the termination of geothermal production to the south. I speculate that an intrusion is present in this region that causes significant perturbation of stress in the field.