Mechanisms of stress- and fluid-pressure-driven fault reactivation in Gonghe granite: Implications for injection-induced earthquakes

We explore the impacts of stress- and fluid-pressure-driven frictional slip on variably roughened faults in Gonghe granite (Qinghai Province, China). Slip is on an inclined fault under simple triaxial stresses with concurrent fluid throughflow allowing fault permeability to be measured both pre- and post-reactivation. Under stress-drive, smooth faults are first slip-weakening and transition to slip-strengthening with rough faults slip-strengthening, alone. A friction criterion accommodating a change in friction coefficient and fault angle is able to fit the data of stable-slip and stick-slip. Under fluid-pressure-drive, excess pore pressures must be significantly larger than average pore pressures suggested by the stress-drive-derived failure criterion. This overpressure is conditioned by the heterogeneity of the pore pressure distribution in radial flow on the fault and is related to the change in permeability. Fault roughness impacts both the coefficient of friction and the permeability and therefore exerts important controls in fluid-injection-induced earthquakes. The results potentially improve our ability to assess and mitigate the risk of injection-induced earthquakes in Enhanced geothermal systems.