Rupture Dynamics of Cascading Earthquakes in a Multiscale Fracture Network.

Fault‐damage zones comprise multiscale fracture networks that may slip dynamically and interact with the main fault during earthquake rupture. Using 3D dynamic rupture simulations and scale‐dependent fracture energy, we examine dynamic interactions of more than 800 intersecting multiscale fractures surrounding a listric fault, emulating a major listric fault and its damage zone. We investigate 10 distinct orientations of maximum horizontal stress, probing the conditions necessary for sustained slip within the fracture network or activating the main fault. Additionally, we assess the feasibility of nucleating dynamic rupture earthquake cascades from a distant fracture and investigate the sensitivity of fracture network cascading rupture to the effective normal stress level. We model either pure cascades or main fault rupture with limited off‐fault slip. We find that cascading ruptures within the fracture network are dynamically feasible under certain conditions, including: (a) the fracture energy scales with fracture and fault size, (b) favorable relative pre‐stress of fractures within the ambient stress field, and (c) close proximity of fractures. We find that cascading rupture within the fracture network discourages rupture on the main fault. Our simulations suggest that fractures with favorable relative pre‐stress, embedded within a fault damage zone, may lead to cascading earthquake rupture that shadows main fault slip. We find that such off‐fault events may reach moment magnitudes up to Mw ≈ 5.5, comparable to magnitudes that can be otherwise hosted by the main fault. Our findings offer insights into physical processes governing cascading earthquake dynamic rupture within multiscale fracture networks. Plain Language Summary: Large geological faults are surrounded by many small fractures of different sizes and orientations, forming a fracture network around the main fault. The characteristics of an earthquake and its size may depend on the orientation of the main fault (and surrounding fractures) within the ambient stress field. Can a small (initial) rupture within a fracture network start a domino‐like (cascading) earthquake across the entire fault network? How does the compounded earthquake process depend on fracture orientation, local stress, and rupture starting point? To address these questions, we study earthquake rupture physics in a complex fault‐zone model comprising over 800 multiscale fracture planes surrounding a main fault. Using 3D dynamic rupture simulations and supercomputing, we explore how different ambient stress orientations, earthquake hypocenters, and levels of fault loading affect earthquake dynamics in fracture networks. The simulations demonstrate that cascading rupture in a fault zone is possible under certain conditions. Our results provide important insights into the physics of cascading earthquakes in multiscale fracture systems and hence are useful for advancing seismic hazard assessment for both natural and induced earthquakes. Key Points: We perform 3D dynamic rupture simulations in a network of >800 fractures and a listric main fault, assuming scale‐dependent fracture energyCascading rupture is possible under high fracture connectivity if a subset of fractures is favorable with respect to the ambient stressWe demonstrate the feasibility of dynamic rupture cascade irrespective of hypocenter locations within the fracture network [ABSTRACT FROM AUTHOR]