Coseismic surface rupture probabilities from earthquake cycle simulations: influence of fault geometry

Abstract. Earthquake surface ruptures are a significant hazard for critical infrastructure and society. Probabilistic Fault Displacement Hazard Analysis (PFDHA) uses empirical and numerical models to estimate the surface rupture likelihood as the first component. However, empirical datasets are often incomplete and limited to few geodynamic settings, reducing their accuracy for site-specific analyses. Moreover, existing models do not capture the influence of physical fault parameters, such as geometry, on surface rupture occurrence nor its spatial variability. We use the RSQSim rate-and-state earthquake simulator to simulate seismicity across twelve alternative geometries of a test fault that incorporate variations of fault connectivity at depth, dip and fault trace sinuosity, aiming for a systematic evaluation of their influence on the probability of primary surface rupture and its spatial variability. Our results show that fault geometry is key in controlling the probability of surface rupture. Models with fault connectivity at depth and greater fault trace sinuosity yield higher probabilities than their counterparts. Conversely, disconnected models limit rupture propagation across segments, reducing surface rupture capability in specific fault regions. This study demonstrates the importance of considering fault geometry when assessing seismic hazards and confirms that earthquake cycle simulators offer a robust tool for next generation PFDHA models.