Effects of pore pressure-dependent friction laws on supershear earthquakes

Supershear earthquakes are a particular class of seismic events in which the rupture velocity exceeds the shear wave velocity. These high-speed ruptures challenge conventional fault mechanics and have significant implications for the assessment of seismic hazards. This work investigates the relationship between pore pressure-dependent friction laws and the propagation of seismic ruptures, particularly the transition to supershear speeds. We present a numerical approach that couples fluid flow, rock deformation, and frictional contact, using stress-rate-dependent rate-and-state friction laws to simulate fault reactivation and rupture propagation. Our simulations demonstrate that the dependence of frictional properties on the effective normal stress rate can partially explain the occurrence of supershear ruptures, leading to a transition from sub-Rayleigh to supershear propagation patterns, as opposed to classical rate-and-state laws. We perform a parametric sweep, varying confining stresses, tectonic ratio, and fluid compressibility, and perform a dimensionless analysis to quantify the impact of hydromechanical parameters on supershear ruptures. Our analysis reveals that the stress drop during rupture is a key parameter in distinguishing between sub-Rayleigh and supershear rupture regimes. This study contributes to understanding the mechanisms that control fault friction behavior and its impact on seismic risk in underground reservoirs, which is crucial for the safe implementation of technologies such as green hydrogen storage and geothermal energy.