Investigation of co-seismic stress and aftershock distribution along the Sagaing fault zone

This study investigated the co-seismic stress and aftershock distribution in the Sagaing Fault Zone (SFZ). The fault parameters of the five strong earthquakes with a M ≥ 6.0 that occurred during 2010–2022 in the SFZ were employed to calculate the Coulomb stress change with numerical modeling techniques resolved on the receiver faults with a similar focal mechanism to the mainshock, strike-slip, thrust, and normal faulting, respectively. The earthquake events were declustered to identify the aftershocks of strong earthquakes in the area. These aftershocks were analyzed spatially to investigate the distribution of aftershocks and the stress changes in the areas. The results indicated that after a strong earthquake occurred in the SFZ, there are two possible patterns of aftershock generation in the area. First, for the strong earthquakes with all types of faulting, the stress changes computed on the receiver faults with similar focal mechanisms to the mainshock revealed that most aftershocks were distributed in areas of increased stress. Second, for the strong earthquakes with oblique faulting, the stress changes computed on the receiver faults with the optimum strike-slip, trust, and normal faulting showed no clear pattern in the distribution of aftershocks; most aftershocks can be generated in both areas of increased and decreased stress. After this study, the M7.7 Myanmar earthquake occurred on 28 March 2025 on the Sagaing fault. The Coulomb stress change analyzed on the receiver faults with similar focal mechanisms to the mainshock indicated that most aftershocks generated in the increased stress areas corresponded to the result obtained from this study.