A rate-and-state friction based criterion for the probability of earthquake fault jumps

Abstract

Geometrical complexities in natural fault zones, such as steps and gaps, pose a challenge in seismic hazard studies as they can act as obstacles to seismic ruptures. In this study, we propose a criterion, which is based on the rate-and-state equation, to estimate the efficiency of an earthquake rupture to jump between two spatially disconnected faults. The proposed jump criterion is tested using a 2D quasi-dynamic numerical simulations of the seismic cycle. The criterion successfully predicts fault jumps where the simpler Coulomb stress change calculation fails to do so. The criterion includes the Coulomb stress change as a parameter but is also dependent on other important parameters among which is the absolute normal stress on the fault the rupture jumps to. Based on the criterion, the maximum jump distance increases with decreasing absolute normal stress, i.e. as the rupture process occurs closer to the Earth's surface or as pore pressure increases. The criterion implies that earthquakes can jump to arbitrary large distances at the Earth's surface if the normal stress is allowed to go to zero, underscoring the potential for large jump distances (i.e. >5 km). We further propose a probabilistic framework to estimate the likelihood of rupture jumps by accounting for uncertainties in fault geometry and earthquake source parameters. Additionally to its role into seismic hazard assessment, this criterion could complement Coulomb stress change maps with those of triggered slip-rates on receiver faults due to quasi-instantaneous stress perturbations, as well as estimates of jump probabilities accounting for parameter uncertainties.