STRESS AND FAULTING IN THE COSO GEOTHERMAL FIELD: UPDATE AND RECENT RESULTS FROM THE EAST FLANK AND COSO WASH
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Conference Proceedings: STRESS AND FAULTING IN THE COSO GEOTHERMAL FIELD: UPDATE AND RECENT RESULTS FROM THE EAST FLANK AND COSO WASH
Abstract
We integrate new geologic mapping and measurements of stress orientations and magnitudes from wells 34-9RD2 and 58A-10 with existing data sets to refine a geomechanical model for the Coso geothermal field. Vertically averaged stress orientations across the field are fairly uniform and are consistent with focal mechanism inversions of earthquake clusters for stress and incremental strain. Active faults trending NNW-SSE to NNE-SSW are well oriented for normal slip in the current stress field, where the mean Shmin orientation is 108° ± 24º in a transitional strike-slip to normal faulting stress regime. These structures bound regions of intense micro-seismicity and are complexly associated with surface hydrothermal activity. WNW-ESE trending faults are also associated with distinct regions of enhanced seismicity but are only associated with surface hydrothermal activity where they intersect more northerly trending normal faults. These faults show no evidence for Quaternary slip at the surface and are poorly oriented in the modern stress field. These results together with stress magnitudes measured in the East Flank of the field suggest that the most productive portions of the Coso geothermal field are in stress environments conducive to normal faulting. In addition, significant horizontal principal stress rotations are recorded by drilling-induced structures in borehole image logs. These variations in the azimuth of induced structures suggest local stress heterogeneity induced by active fault slip and are consistent with the high rates of seismicity observed in the geothermal field.
- Authors
- Davatzes, N.C.; Hickman and S.H.
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Citation
Davatzes, N.C.; Hickman, S.H.. 1/1/2006. STRESS AND FAULTING IN THE COSO GEOTHERMAL FIELD: UPDATE AND RECENT RESULTS FROM THE EAST FLANK AND COSO WASH. Proceedings of (!) ;
(!) : PROCEEDINGS, Thirty-First Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 30-February 1, 2006.
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