Active Fault Controls at High-Temperature Geothermal Sites: Prospecting for New Faults

Abstract

Our previous studies found spatial associations between seismically active faults and high-temperature geothermal resources in the western Basin and Range, suggesting that recency of fault movement may be a useful criterion for resource exploration. We have developed a simple conceptual model in which recently active (Holocene) faults are preferred conduits for migration of thermal water from deep crustal depths, and we infer that the detection of sites of recent crustal strain (i.e., large surface-rupturing earthquakes) may be an effective exploration tool. To further explore this model, we studied several known geothermal resource areas to determine the level of unrecognized active faults present in these areas. Analysis of low-sun-angle aerial photography acquired over the Needle Rocks, Astor Pass, Empire, and Lee/ Allen hot springs areas indicates that many unrecognized active faults are present. A detailed analysis was conducted of the northern Pyramid Lake-Smoke Creek Desert-San Emidio Valley fault system, and we found that many newly recognized active faults delineate a complex pattern of extensional strain release across several basins containing geothermal resources.