Three-dimensional P and S waves velocity structures of the Coso geothermal area, California, from microseismic travel time data

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Journal Article: Three-dimensional P and S waves velocity structures of the Coso geothermal area, California, from microseismic travel time data

Abstract
High precision P and S wave travel times for 2104 microearthquakes with focus <6 km are used in a non-linear inversion to derive high-resolution three-dimensional compressional and shear velocity structures at the Coso Geothermal Area in eastern California. Block size for the inversion is 0.2 km horizontally and 0.5 km vertically and inversions are investigated in the upper 5 km of the geothermal area. Spatial resolution, calculated by synthetic modeling of a cross model at critical locations, is estimated to be 0.35 km for V (sub p ) and 0.5 km for V (sub s ) . Model uncertainties are estimated by a jackknife approach and simulation of random and associated picking errors. Low-velocity zones for both P and S waves are identified at geothermal production depths (1-3 km). A large, low V (sub p ) (-6%) zone is found at depth 2-2.5 km 2 km southwest of Sugarloaf Mountain where high attenuation has been previously reported. However, a general high- V (sub p ) zone is seen under Coso Hot Springs with a slightly low V (sub s ) zone, which is characteristic of fluid saturation. The overall distributions of V (sub p ) and V (sub s ) perturbations do not correlate. An isolated high- V (sub s ) (+9%) feature, about 2 km in diameter, is unambiguously seen 2 km due west of Sugarloaf extending from surface to depth. This feature is surrounded by a circular, low- V (sub s ) belt of approximately 1 km width. The surrounding belt is probably the cracked, high-porosity reservoir/conduit of geothermal fluid flow. In the 2 km southwest Sugarloaf region, we found low V (sub p ) and high V (sub s ) at geothermal production depths from 1 to 2.5 km. Combined with attenuation results, this may represent a hot, fluid-depleted center of magmatic activity.

Authors 
Wu, H.; Lees and J.M.  








Published Journal 
Journal of Geophysical Research, 6/1/1999





DOI 
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Citation

Wu, H.; Lees, J.M.  . 6/1/1999. Three-dimensional P and S waves velocity structures of the Coso geothermal area, California, from microseismic travel time data. Journal of Geophysical Research. (!) .


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  1. Coso Geothermal Area
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