On the role of thermal stress and fluid pressure in triggering seismic and aseismic faulting at the Brawley Geothermal Field, California.

Surface deformation and earthquake swarms are correlated in space time with operations at the Brawley geothermal field southern California. The seismicity culminated 2012, about 2 years after onset of activity, a M5.4 earthquake. These earthquakes occurred >5km depth, much larger than ∼1km reach wells, raising questions triggering mechanism. shows that aseismic slip on normal fault intersecting reservoir preceded swarm possibly triggered it. In this study, we resort to geomechanical modeling investigate how sequence seismic unfolded. accounts for thermo- poro-elastic stress changes induced by allows inelastic faulting surrounding medium. simulation successfully reproduces flow rates well-head pressures reported operator as well measured surface subsidence. By varying model parameters, show subsidence is due thermal contraction faulting. reactivation driven pressure unclamping. pressure-driven rapid influences area, while temperature-driven more gradual localized near injection wells. our simulation, operation leads elastic release via yielding within volume and, conversely, build-up beneath reservoir, where 2012 developed. Such transfer provides plausible explanation swarm. Our study can, principle, contribute hazard mitigation through tectonic stresses but points difficulty mitigating posed transfers area.