Reservoir Induced Seismicity Modelled Using a Fully Coupled Poro-Visco-Elasto-Dynamic Model with Frictional Contact and Rate-and-State Dependent Friction: Dynamics of Spontaneous Coseismic Rupture

Reservoir-induced seismicity (RIS) is a critical concern in geo-engineering, arising from the coupled interactions among in-situ stress, fluid flow, and fault mechanics, associated with reservoir impoundment. Improving our understanding of earthquake dynamics is therefore essential for elucidating the dynamics of rupture processes at RIS. In particular, understanding fault reactivation and the transition from quasi-static aseismic slip to dynamic rupture is crucial, as the nucleation phase may provide valuable information for detecting pre-seismic signals and estimating earthquake magnitudes.

We develop a novel two-dimensional, fully coupled poro-visco-elasto-dynamic finite-element model (implemented in COMSOL) to simulate RIS under reservoir impoundment in extensional tectonic settings. The porous medium is represented as a Kelvin–Voigt poro-visco-elastic solid to capture elastic deformation and intrinsic damping, while inertial effects are included to resolve rupture dynamics and seismic wave propagation. The fault is modeled as  non-penetrating surfaces enforced using an augmented Lagrangian contact formulation and governed by rate-and-state friction, where fault deformations are tolerated by using a virtual thin layer capability.

Model results show that when frictional and hydromechanical conditions permit fault reactivation, slip may become unstable and transition into a coseismic event, with rupture propagating along the fault in asymmetric two–crack-tip–like slip pattern emanating from the hypocenter. Rupture propagation speed is higher in the stiffer rock than in the softer one. Preferential flow induced by the reservoir impoundment forces the rupture nucleation earlier. Porosity and permeability of the fault damage zone decrease with depth (higher than that of the ambient rock at the upper part of the fault), providing the conduit for fluid flow over the fault and promoting longer rupture lengths at RIS.

These findings highlight the critical role of mechanical and hydraulic properties in controlling nucleation and rupture processes in RIS, with important implications for the design and management of reservoir impoundment.