Stress and fluid transfer in a fault zone due to overpressures in the seismogenic crust

Stress and fluid transfers were analyzed on the surface of a 30 m thick dextral strike-slip fault zone subjected to an overpressure of 63 kPa. Pressure-strain measurements taken during the pressurization indicated a strain state primarily controlled by the hydromechanical behavior of permeable fractures, and then, by the fluid diffusion in the matrix. Using THM modeling, we simulated an extension of these hydromechanical effects to a 25 km depth in the seismogenic crust, applying a lithostatic pressure at the base of the fault. The simulations indicate that a significant strain in the damage zone greater than that in the protolith, along with the differences in hydraulic diffusivity between the damage zone and protolith, may induce high static stress and fluid accumulations in the core. Under this stress, this core is projected to exhibit deformity - as much as a 12 m shear slip distributed over a 175 m long active zone.