Mechanisms and Seismological Signatures of Rupture Complexity Induced by Fault Damage Zones in Fully‐Dynamic Earthquake Cycle Models.

Damage zones are common around faults, but their effects on earthquake mechanics are still incompletely understood. Here, we investigate how damage affects rupture patterns, source time functions (STF) and ground motions in 2D fully‐dynamic cycle models. We find that back‐propagating rupture fronts emerge in large faults and can be triggered by residual stresses left by previous ruptures or by damage‐induced pulse‐to‐crack transitions. Damage‐induced back‐propagating fronts are modulated by slip rate oscillations, amplify high‐frequency radiation, and sharpen the multiple peaks in STF even in the absence of frictional heterogeneity or fault segmentation. Near‐field ground motion is predominantly controlled by stress heterogeneity left by prior seismicity, and further amplified within the damage zone by trapped waves and outside it by secondary rupture fronts. This study refines our knowledge on damage zone effects on earthquake rupture and identifies their potentially observable signatures in the near and far field. Plain Language Summary: Faults are surrounded by layers of fractured rocks, known as damage zones, which can affect earthquakes and related hazards, but in ways that are still not well understood. Here, by running computer simulations, we investigate how damage zones influence earthquake ruptures and consequent ground motions. Our models fully account for seismic wave effects, produce multiple earthquake cycles, and span a large range of fault lengths and damage zone properties that are representative of natural faults. We identify characteristic patterns of earthquake rupture produced by damage zones: back‐propagating fronts that re‐rupture the fault, and oscillatory fault motions that affect ground shaking amplitude and frequency content. We identify which of these effects might be observable in seismograms recorded near and far from the fault. Overall, our computational study highlights significant effects of damage zones on earthquakes and on the shaking they produce. These results can guide us to better interpret earthquake source and ground motion observations, and to predict the potential characteristics of future events. Key Points: Reduction of nucleation size and pulse‐crack transitions are two distinct damage zone effects that induce back‐propagating rupture frontsDamage effects can enhance high‐frequency radiation and complexity of source time functions, potentially observable in the far fieldBack‐propagating fronts have potential signatures in near‐field seismograms and can affect peak ground motions [ABSTRACT FROM AUTHOR]