Analysis of Cause and Mechanism for Injection-Induced Seismicity at The Geysers Geothermal Field, California

Abstract

We analyzed relative contributions to the cause and mechanism of injection-induced seismicity at The Geysers geothermal field, California, using coupled thermal-hydrological- mechanical modeling. Our analysis shows that the most important cause for injection-induced seismicity is injectioninduced cooling and associated thermal-elastic shrinkage that changes the stress state in such a way that mechanical failure and seismicity can be induced. Specifically, the cooling shrinkage results in unloading and associated loss of shear strength in critically shear-stressed fractures, which are then reactivated. Thus, our analysis shows that cooling-induced shear slip along fractures is the dominant mechanism of injection-induced seismicity at The Geysers.