FEM‐Peridynamic Modelling of Supershear Earthquake Ruptures in Dry and Fluid‐Saturated Media

Since ground shaking increases with rupture speed during earthquakes, the velocity transition from sub‐Rayleigh to supershear in mode II fracture is crucial for the propagation of seismic ruptures and associated strong ground motions. We employ a newly conceived 2‐dimensional hybrid Finite Element Method and Peridynamic (FEM/PD‐2D) model to investigate the transition from sub‐Rayleigh to supershear in dry and fluid‐saturated media. The FEM is used to simulate fluid flow, while PD is used to describe solid deformation. We first verify the results of the FEM/PD‐2D model against two experimental configurations: (a) rupture propagation along a Homalite plate with a pre‐notch subjected to impact shear loading and, (b) rupture propagation along a friction interface between two PMMA blocks. Once the robustness of the FEM/PD‐2D model has been verified, we apply it to explore rupture propagation along both dry and fluid‐saturated media under shear loading. Supershear crack speeds and the emergence of shear Mach cones are observed in both the dry and fluid‐saturated cases. Supershear rupture can be achieved through either the indirect (mother‐daughter cracks or Burridge‐Andrews mechanism) or a direct transition. In particular, under fluid‐saturated conditions, a frequent situation in natural fault zones but overlooked in previous studies, the direct transition from sub‐Rayleigh to supershear is favored by poroelastic effects near the rupture front.