Mainshock‐Induced Stress Changes Modulate Initial Aftershocks on Complex Branching Faults of the 2019 Ridgecrest Earthquake

Abstract Large earthquakes can activate complex aftershock fault networks. In such systems, what controls the spatiotemporal evolution of early aftershocks remains a critical yet unresolved problem. Here, using the 2019 M 7.1 Ridgecrest earthquake as an example, we partition the first 10 days of aftershocks onto 15 branching faults activated by the mainshock. For each branching fault, we assess the spatial and temporal influence of mainshock‐induced Coulomb failure stress change (ΔCFS) on aftershock patterns and b values. We find that positive ΔCFS may promote aftershock occurrence across multiple faults during the initial 3 days following the mainshock, but this effect diminishes afterward. Moreover, on most branching faults, higher aftershock b values tend to be associated with areas experiencing negative ΔCFS and reduced differential stress. These findings indicate that mainshock‐induced stress plays an important role in controlling initial aftershock generation and size‐frequency characteristics, providing constraints on aftershock forecasting in complex fault systems.