Hydro-Mechanical Modeling of Fluid-Regulated Deformation in Accretionary Wedges and Its Implications for Megathrust Slip

Understanding the physical mechanisms governing megathrust seismicity and the geodynamic feedback between the megathrust and the overriding accretionary wedge remains critical in subduction zone geophysics. The structural complexity of accretionary wedges—characterized by heterogeneous porosity, permeability, and fault networks—critically influences the configuration of pore fluid pressure and frictional properties along the megathrust interface. To investigate these interactions, we employ a fully coupled hydro-mechanical numerical model (Gerya, 2019) that simulates two distinct timescales within a single, consistent rheological framework. Our approach incorporates temperature-dependent dehydration reactions, including smectite-to-illite and zeolite-to-greenschist transitions, to evaluate how fluid production and migration evolve during both subduction and seismic processes. Additionally, we implement a dynamic fault-valving mechanism where reference permeability evolves transiently to mimic fracture-induced permeability enhancement during fast slip. The simulation follows a two-stage workflow: first, we conduct long-term wedge accretion modeling with adaptive time steps (10–500 years) using a higher stress tolerance to construct realistic wedge architectures. Subsequently, we switch to a rupture simulation mode by reducing the stress tolerance, allowing the adaptive time-stepping scheme to automatically resolve short-term seismic cycles (from days to years). This methodology successfully introduces the structural and hydrological complexity inherited from long-term geological evolution into the analysis of short-term megathrust slip behaviors. Results indicate that fast slip events preferentially initiate at the transition zones between low and high overpressure regions, whereas domains characterized by high pore fluid pressure ratios () predominantly host slow slip events. Furthermore, we find that hydraulic properties control the spatiotemporal stability of rupture nucleation: higher permeability promotes significant temporal pore pressure variability, resulting in scattered initiation depths, while lower permeability maintains stable pressure configurations, leading to spatially consistent rupture nucleation. We conclude that the long-term hydro-mechanical evolution of the wedge governs megathrust nucleation and slip segmentation.