Stress Barriers and Their Impact on Rupture Propagation

Abstract Earthquake ruptures often exhibit complex behaviors, including abrupt arrest followed by delayed re‐nucleation. While on‐fault stress heterogeneity is a recognized contributing factor, as it can arrest or slow down rupture propagation, its interaction with propagating ruptures remains complex and not fully understood. Here, we study frictional ruptures under controlled laboratory conditions by imposing a heterogeneous stress field along an artificial fault. This setup consistently led to the spontaneous emergence of a well‐defined stress barrier. Our results show that the presence and strength of the stress barrier systematically influence rupture propagation, sometimes in non‐trivial ways. As expected, strong barriers tend to arrest ruptures, while weaker ones reduce their velocity, inducing a time delay in the rupture propagation. However, we also observe several less‐intuitive outcomes, including static triggering, barrier‐induced supershear transition, and dynamic triggering. We elucidate the physics behind each interaction mechanism through Linear Elastic Fracture Mechanics (for the arrest and deceleration mechanisms) and the Rate‐and‐State framework (for the static triggering). Interestingly, static triggering and barrier‐induced supershear transitions can enable rupture propagation beyond barriers that are expected to arrest ruptures. Similarly, dynamic triggering can accelerate the onset of rupture beyond barriers that decelerate ruptures. Moreover, our experiments show that the barrier efficiency evolves over successive earthquake cycles, weakening with repeated partial ruptures and becoming permanent once complete ruptures break through the fault. This experimental study underscores the critical role of stress heterogeneity in controlling the dynamics of frictional ruptures and offers new insights into the physics of delayed rupture triggering.