Numerical investigation of the role of Thermal pressurization in the faults frictional response under large coseismic slip.

We study the role of thermal pressurization in the frictional response of a fault under large coseismic slip. We investigate the role of the seismic slip velocity, mixture compressibility, characteristic grain size and viscosity parameter in the frictional response of the coupled Thermo-Hydro Mechanical problem, taking into account the faults microstructure. We start from the mass, energy and momentum balance equations for Cosserat continua and we combine them with an elasto-(visco-)plastic material law using perfect plasticity and Perzyna viscoplasticity. We investigate both the rate independent as well as the rate dependent frictional response and compare with existing models found in literature, namely the rate and state friction law. We show that our model is capable of predicting strain rate hardening and velocity softening without the assumption of a state variable. We observe traveling instabilities inside the layer that lead to oscillations in the faults frictional response (see Figure 1), a phenomenon similar to the case of Portevin Le Chatelier (PLC) instability. This behavior is not captured by the existing model of uniform shear (Lachenbruch, 1980) and shear on a mathematical plane (Rice, 2006), which predict a strictly monotonous behavior during shearing. Experimental analyses, which have managed to insulate Thermal pressurization from the other weakening mechanisms (Badt et al., 2020) corroborate our numerical results.