Modelling fluid transfer and slip in a fault zone when integrating heterogeneous hydromechanical characteristics in its internal structure

Fluid pressure has significant effects on the mechanical behaviour of fault zones, because it can change dramatically throughout the earthquake cycle. Here, we discuss how the heterogeneity of the fault materials affects the fluid transfer and slip processes in and around a fault zone. We present a numerical analysis of the interaction between fluid, stress and the development of slip in a fault zone with heterogeneous hydromechanical characteristics through the brittle seismogenic portion of the crust. In the model, the fault core, characterized by a low permeability and Young's modulus, is surrounded by a high permeability and more rigid damage zone with spatial variations of the hydromechanical properties. Strain-dependent porosity and permeability equations are specified, and the inelastic response of the material is described by a Coulomb criterion. This study shows various evolutions of fluid overpressure, stress, and slip along the principal shear zone depending on the heterogeneity of the fault. The analysis suggests that a pressure pulse can trigger earthquakes by reducing the effective normal stress of the fault, and that the size of the slip zone and the magnitude of the slip are significantly affected both by the reduction in fault effective strength and by the increase in fault porosity and permeability.