Microphysical Modeling of Fault Slip and Stability Transition in Hydrothermal Conditions

Field and laboratory observations indicate that the frictional behaviors of faults depend on hydrothermal conditions. We extend the microphysical Chen-Niemeijer-Spiers (CNS) model to hydrothermal conditions by using the observed temperature variation of indentation hardness to infer the temperature dependence of a microphysical para....meter (........similar to). This parameter is assumed constant in previous versions of the CNS model. A simple spring-slider system is used to simulate the fault system and investigate the steady-state frictional behaviors of wet granite gouges. Our numerical results quantitatively reproduce experimental data showing the frictional-plastic transition. The results also describe the transition from velocity-strengthening at low temperatures (<160 degrees C), to velocity-weakening at intermediate temperatures (160 degrees C-370 degrees C), then back to velocity-strengthening at high temperatures (>370 degrees C). In our extended CNS model, these results suggest that the dominant shear deformation mechanism does transition from frictional granular flow to fully plastic creep with increasing temperature. Plain Language Summary Rapid fault slip in the Earth's crust is generally observed at a depth of similar to 3-40 km where the temperature range is similar to 150 degrees C-350 degrees C. A transition from slow to rapid and back to slow slip with increasing temperature has been observed in laboratory experiments under realistic conditions. However, the underlying mechanisms remain unresolved. We extend a previous model based on microscale processes by including additional temperature dependence. We use this extended model to explore the frictional behaviors of granite gouges under conditions representative of the crust. Our numerical results are quantitatively consistent with experimental data and natural observations, in particular, the temperature-dependent frictional-plastic transition and depth distribution of earthquakes.