When Earthquakes Cross the Gap: Physics-Based Dynamic Modeling of Stepover Jumps in Normal Faults

Abstract

Understanding the mechanisms that enable earthquakes to jump across stepovers in fault systems is essential for improving seismic hazard assessment. Although many previous studies focused on strike-slip fault systems, the physics of rupture jumping across normal faults remains less investigated. In this study, we perform a series of 3D dynamic rupture simulations to explore the key factors that govern rupture jumps across normal-fault segments. By systematically varying critical parameters such as prestress levels, principal stress orientation, the distance between emitting and potentially triggered faults, and their relative positions, we identify conditions and dynamic effects that allow ruptures to successfully jump stepovers of up to 5 km. Our findings provide insights into why some dynamically triggered events propagate as self-sustained runaway ruptures, while others are rapidly self-arrested after nucleation. Our results highlight the trade-offs between the stress-shadowing effect, relative fault positioning, fault proximity, and stopping phases. For instance, fault geometry introduces a fundamental trade-off: closely spaced fault sections enhance rupture-jump potential, yet do not necessarily favor larger magnitudes. For very closely spaced faults, stress-shadowing suppresses slip and limits magnitude, whereas at larger gaps, where the shadow weakens, the rupture can grow and release more energy. Our simulations show that the largest magnitudes occur in configurations where the receiver fault lies on the hanging wall of the emitter fault at specific overlap and gap distances, highlighting the strong geometric control on multifault earthquake behavior for normal faults. Furthermore, the simulations reveal that the static Coulomb stress change approach, commonly used to predict rupture connectivity, does not fully capture the complexities of dynamic rupture processes across normal-fault systems: Dynamically jumping between normal-fault segments is more rare than static criteria would suggest.