Seismic Fault Weakening Due To Thermal Pressurization of Comminution‐Induced Hydrophilic Talc

Abstract Talc is generally considered to be frictionally stable, yet the mechanochemical effect of extensive comminution along the fault gouge remains poorly understood. Here, we report that intact hydrophobic crystalline talc was mechanochemically changed into hydrophilic talc, by comminution using high‐energy ball milling. The weight fraction of water on the intact talc was close to zero, which gradually increased to approximately 0.13 with comminution. Then, we performed thermo‐mechanical‐chemical numerical modeling of thermal pressurization (TP) under seismic slip with parameterization of the water content of hydrophilic talc. In the comminuted hydrophilic talc model, the effective shear stress of the talc‐bearing fault patch converges to near zero, accompanied by pore pressure buildup due to seismic frictional heating and TP. Our results highlight that a fault containing the comminuted talc has the potential to exhibit slip‐weakening frictional behavior and catastrophic fault rupture, beyond the previous thought that the talc is frictionally stable with slip‐strengthening.