A major goal in earthquake physics is to derive a constitutive framework for fault
slip that captures the dependence of shear strength on fault rheology, sliding velocity,
and pore-fluid pressure. In this study, we present H-MEC (Hydro-Mechanical Earthquake
Cycles), a newly-developed two-phase flow numerical framework ??? which couples solid
rock deformation and pervasive fluid flow ??? to simulate how crustal stress and fluid
pressure evolve during the earthquake cycle. This unified, continuum-based model,
incorporates a staggered finite difference???marker-in-cell method and accounts for
inertial wave-mediated dynamics and fluid flow in poro-visco-elasto-plastic compressible
medium. Global Picard-iterations and an adaptive time stepping allow the correct resolution
of both long- and short-time scales, ranging from years to milliseconds. We present
a comprehensive in-plane strike-slip setup in which we test analytical poroelastic
benchmarks of pore-fluid pressure diffusion from an injection point along a finite
fault width. We then investigate how pore-fluid pressure evolution and solid???fluid
compressibility control sequences of seismic and aseismic fault slip. While the weakening
phase is controlled by localized compaction of pores and dynamic self-pressurization
of fluids inside the undrained fault zone, the subsequent propagation of dynamic ruptures
is driven by pore-pressure waves. Furthermore, pore-fluid pressure conditions on the
fault and shear strength weakening associated with rapid selfpressurization of fluids
control the characteristic slip-weakening distance, the final size of seismic events,
and the scaling between slip and fracture energy observed for large earthquakes. Our
modeling results demonstrate that fault failure can occur due to poroelastic coupling
on a finite-width shear zone, thus highlighting the importance of considering the
realistic hydro-mechanical structure of faults to investigate fluid-driven seismic
and aseismic slip, either as a natural process or induced by human activities.
