Geothermal Tectonics of the Imperial Valley as Deduced from Earthquake Occurrence Data

Abstract

An analysis of spatial and temporal change in the mode of earthquake occurrence allows identification of regions where episodes of tensional strain release have occurred. Temporal analysis of the coefficients in the recurrence relation log (NC) = a-b (MAG) is required because in regions like the Imperial Valley the average values of the coefficients in this equation are dominated by events involved with the release of regionally accumulating shear strain. The spatial distribution of this average b coefficient can only indicate a detailed temporal decomposition for two areas, one centered on the presumed region of spreading at the southern end of the Salton Sea and one centered approximately on the Heber geothermal anomaly. We conclude based on b coefficient temporal change that events of Oct. 27, 1963 located at the Niland geothermal anomaly involved tensional strain release.