Mechanism of induced seismicity at the Geysers Geothermal Reservoir, California

Abstract

The Geysers reservoir is situated in a 60–80 km‐wide right‐lateral shear zone associated with the North American‐Pacific plate boundary. A small fraction of the shear may be occurring as permanent aseismic creep, which is being converted to stick‐slip movement in The Geysers reservoir due to steam production. Two mechanisms could be responsible for the induced seismicity: a large (>100 bars) increase in effective rock pressure; and an increase in the coefficient of friction. The first mechanism requires that the initial state of the reservoir be predominantly liquid‐dominated. The second mechanism is a consequence of dehydration of the reservoir causing both the ‘hardening’ of clay and fault gouge, and the precipitation of silica.