Abstract

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 20kPa in the basement and sedimentary cover, but the seismicity rate in the sedimentary cover is 4 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.