Mineralogy Controls on Injection‐Induced Fault Slip

Abstract Fault rocks vary in mineralogy but understanding the role of mineralogy in injection‐induced fault slip behavior remains challenging. We conduct laboratory fluid injection experiments on representative faults with distinct surface mineralogy, injecting fluid at a constant rate of 0.6 mL/min and under a confining pressure of 20 MPa, to examine how mineralogy affects fluid‐driven slip and seismicity. We find that the fault surface with a higher content of tectosilicates (quartz, microcline, albite, totaling 96%) exhibit higher shear strength. The tectosilicate‐rich fault takes a longer time to reactivate but accumulates seismic moment more rapidly, indicating more intense seismicity. In contrast, the fault containing abundant phyllosilicates (50% biotite) promotes a transition from unsteady stick‐slip to steady slip during fluid injection. Stick‐slip events in the tectosilicate‐rich fault exhibit higher peak slip rates and greater slip displacements. We propose a microscopic mechanism to elaborate how fluids may influence mineral friction and thereby affect injection‐induced fault slip.