The role of fluids in earthquake cycles: insights from seismo-hydro-mechanical models

Understanding the role of fluids in earthquake mechanisms and designing a computational framework which couples solid rock deformation and fluid flow is a major challenge in geosciences. We present results from a newly developed Hydro-Mechanical Earthquake Cycle (H-MEC) numerical code, which can resolve inertia- and fluid-driven seismic events, as well as long-term deformation in and off-fault. The two-dimensional (2-D) code uses a finite difference method with rate dependent strength, while an adaptive time-stepping allows the correct resolution of both long- and short-time scales, ranging from years during slow tectonic loading to milliseconds during the propagation of dynamic ruptures. We investigate the evolution of a simple strike-slip fault with fluid flow in a poro-visco-elasto-plastic compressible media. We analyze which parameters could have a first-order control on the seismic and aseismic slip behavior. In particular, we explore  the effects of fault permeability, shear modulus and the rate-strengthening yield strength. Our results suggest that the mentioned parameters influence the recurrence time of seismic cycles. Furthermore, permeability controls the long-term slip behavior and has a significant impact on the self-pressurization of pore-fluid pressure inside the fault zone, both during earthquake nucleation and propagation. Notably, for a range of different fault permeability a temporal transition from seismic events to aseismic slip can be observed, due to a gradual increase of pore-pressure over multiple earthquake cycles. This new numerical framework can help us better understand earthquake mechanisms and earthquake cycles, the role of fluids along fault-structures, and their effect on long term geodynamic processes.