Structural and frictional controls on the nucleation, propagation, and arrest of the 2025 Mw 6.2 Central Marmara Earthquake, Türkiye

How large earthquakes initiate, propagate, and ultimately arrest remains a central question in seismology, particularly in high-risk regions such as the Istanbul metropolitan area, home to more than 20 million people. The 2025 Mw 6.2 Central Marmara earthquake ruptured a ~20 km-long segment of the right-lateral east-west trending North Anatolian Fault Zone beneath the Sea of Marmara (hereafter NAFZ-Marmara), immediately adjacent to a long-recognized Istanbul seismic gap. The ruptured fault segment belongs to a complex, structurally heterogeneous system, bounded by a creeping segment to the west and a locked segment to the east. This setting allows us to investigate how slip heterogeneity may control rupture behavior.

Here, we combine newly derived seismicity and focal mechanism catalogs spanning both the pre- and post-mainshock periods with strong-motion back-projection imaging to constrain earthquake nucleation processes and to characterize rupture propagation, aftershock evolution, and triggered seismicity. We observe that roughly two weeks before the mainshock, seismicity subtly localized and migrated ~10 km toward the future epicentral area from the west, within a portion of the NAFZ-Marmara characterized by high creeping rates and the presence of repeating earthquakes. Back-projection reveals that the mainshock rupture propagated unilaterally ~24 km eastward through a sedimentary basin at velocities approaching the shear-wave speed, but without evidence of supershear behavior, before abruptly arresting upon reaching a topographic high. Notably, immediately ahead of the eastern rupture tip, aftershock activity is very sparse. In contrast, no evidence is found for rupture propagation toward the west, suggesting that the creeping segment inhibited rupture growth in that direction. This is further supported by the aftershock migration pattern to the west, which evolves approximately logarithmically with time, consistent with afterslip-driven aftershocks.

Despite the abrupt rupture arrest at the eastern rupture tip, the earthquake triggered intense seismicity in a region located ~15–20 km south of Istanbul, spatially disconnected from the actual rupture, but kinematically linked to the NAFZ-Marmara system. The timing and source kinematics of the triggered events, occurring within minutes to days and persisting for months after the mainshock, indicate a strong response of the surrounding fault network to the stress perturbations imposed by the rupture.

Our results show that the 2025 Mw 6.2 Central Marmara earthquake ruptured a complex fault system in which frictional and structural heterogeneities strongly modulated rupture nucleation,  propagation, arrest, and the spatiotemporal pattern of aftershocks and triggered seismicity. Finally, we highlight that the abrupt eastern rupture termination and the activation of faults immediately south of the Istanbul megacity are particularly significant in the context of the region’s seismic hazard assessment.