Abstract

Earthquake activities in the Salton Sea geothermal field were monitored for 8 weeks in 1975 with an array consisting of five portable seismographs and two USGS permanent stations. Two to three events per day (ML < 3.0), commonly occurring in clusters along with intermittent swarm activities, characterize the seismicity of the study area. Focal depths decrease toward the geothermal area where they range from 0.5 to 3.5 km, suggesting aseismic creep occurs at higher temperature regime in the deeper part. The previously inferred Brawley fault is probably offset into two segments but connected by a leaky transform fault where the crustal spreading is reflected by normal faulting in one earthquake swarm and the crustal shearing by strike-slip faulting in another more active swarm. The activities of the latter swarm were poorly correlated with tidal gravity.

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