Surface Deformation and Seismicity Induced by Poroelastic Stress at the Raft River Geothermal Field, Idaho, USA

We investigate the relative importance of injection and production on the spatial-temporal distribution of induced seismicity at the Raft River geothermal field. We use time-series of InSAR measurements to document surface deformation and calibrate a hydro-mechanical model to estimate effective stress changes imparted by injection and production. Seismicity, located predominantly in the basement, is induced primarily by poroelastic stresses from cold water reinjection into a shallower reservoir. The poroelastic effect of production from a deeper reservoir is minimal and inconsistent with observed seismicity, as is pore-pressure-diffusion in the basement and along reactivated faults. We estimate an initial strength excess of ∼20 kPa in the basement and sedimentary cover, but the seismicity rate in the sedimentary cover is four times lower, reflecting lower density of seed-points for earthquake nucleation. Our modeling workflow could be used to assess the impact of fluid extraction or injection on seismicity and help design or guide operations.