Seismicity and seismic stress in the Coso Range, Coso geothermal field, and Indian Wells Valley region, southeast-central California (original) (raw)

The temporal and spatial distribution of seismicity in the Coso Range, the Coso geothermal field, and the Indian Wells Valley region of southeast-central California are discussed in this paper. An analysis of fault-related seismicity in the region led us to conclude that the Little Lake fault and the Airport Lake fault are the most significant seismogenic zones. The faulting pattern clearly demarcates the region as a transition between the San Andreas-type strike-slip regime to the west and the Basin and Range extension regime to the east. We present the spatial and temporal variations in seismicity immediately following significant earthquakes in nearby regions from 1983 to 1999 with special emphasis on larger earthquakes (M Ն 5) in 1995-1998. The Ridgecrest earthquakes of 1995 show a complicated faulting pattern as the rupture changed from normal slip to right slip at depth. The interrelationships between the Coso Range earthquakes of 1996 and 1998 are presented as a set of conjugate events. Analysis of earthquake source mechanisms shows evidence for lateral variations in the faulting pattern in southeast-central California. Earthquake focal mechanisms are used to estimate local stress orientation within the Coso geothermal field. We have identified a boundary between a transpressional regime and a transtensional regime inside the field that correlates with observed spatial variations of heat flow and seismic attenuation, velocity, and anisotropy.