Controls of temperature on seismic moment released from reactivated faults

Induced seismicity is the main uncertainty to safely produce geothermal energy, raising questions as to how applicable known physical laws are at increased temperatures. We explore the impact of elevated temperatures on maximum seismic moments anticipated in induced seismicity. We conduct laboratory reactivation experiments on a single inclined fracture (SIF) at equilibrated temperatures of 23 °C, 78 °C and 137 °C. Fractures are loaded at a constant shear stress of ∼80 % of the peak shear strength with slip activated by fluid injection. Reactivated seismic moments scale linearly with volume injected but decrease by one-order-of-magnitude with incremented temperatures over the range 23–137 °C. We provide a new perspective of temperature influence on fracture shearing – emphasizing the role of fracture properties (stiffnesses) of elastic tangential and normal stiffnesses on the energetics of slip. We use these stiffnesses to define a relationship linking injected volume to the resulting seismic moment. In transiting from 23 °C to 137 °C, tangential stiffness is halved and normal stiffness quadrupled, thus the resulting seismic moment is potentially reduced by a factor of eight – congruent with observations of reactivated seismic moments over the same temperature range. The change in stiffness can be explained by an increasing contact area, which we also observe by P wave measurements. Our results suggest that increased temperature inhibits fault seismicity and the expected maximum seismic moment of induced seismicity.