ACTIVE FAULTS AND ASSOCIATED TECTONIC STRESS IN THE COSO RANGE, CALIFORNIA

The Coso Range contains faults that have been active in the Holocene. Some of these faults have moved about 100 years ago, possibly with the 1872 Owens Valley earthquake. Exploratory trenches exposed offsets up to 3.4 meters for one faulting event. Thus, a magnitude of 7.5 could be expected on these faults based on displacement versus length equations. Recent local and regional earthquakes have caused property damage in the city of Ridgecrest.; The tectonics of the Coso Range have been described as having arcuate and ring faults both of which suggest the presence of a circumscribed subsidence bowl or caldera-like feature. Data presented in this paper suggest the tectonism of the Coso Range is in transition between stresses from the right-slip, San Andreas fault-plate interaction and the extensional tectonics of the Basin and Range province. Arcuate faults in the Coso Range are interpreted to have been produced by the regional stress field, rather than being from volcanogenic origin. Focal mechanisms of small-magnitude earthquakes support the stress directions indicated by local fault patterns. Fumeroles in the area are primarily associated with oblique-slip faults, rather than with arcuate or ring faults. The geothermal reservoir is, therefore, much different from that of a caldera or subsidence bowl, and the overall geothermal potential is probably less than the earlier estimates.; This diverse structural zone between the Sierra Nevada and Walker Lane could be caused by a clockwise rotation of the Sierra Nevada Range about its northern axis.