A thermo-chemo-mechanical model for fault friction
A substantial decrease of the apparent friction has been observed in many experiments performed on synthetic or recovered fault gouges or bare rocks at seismic slip rates for different materials. This phenomenon has major implications to understand the creation of earthquakes in the brittle part of the lithosphere. These observations have become possible thank to the development of experimental machines that allow to shear the material at high velocities (up to 1m/s) under moderately high normal stresses (up to 20 MPa). In this study, we show that the weakening of the apparent friction coefficient can be explained by thermochemo-mechanical mechanisms. We model the fault core as an infinite sheared layer and use thermo-chemo-mechanical couplings to account for the most important processes involved in a fault zone and in the laboratory experiments. In particular, the increasing velocity during a seismic slip induces a temperature rise, which can trigger phase transformations that affect the shear stress of the system. The evolution of friction at steady state obtained from the model fits adequately results of experiments performed on various materials such as clay, halite, carbonate, granite, serpentinite and silicate.
