Little Murray Ridge Subduction Controls the Segmentation of Megathrust and Co-Seismic Rupture Along the Eastern Makran Margin

Abstract

Whether subducted seafloor topography can generate or inhibit large earthquakes is a long-standing debate, primarily due to the lack of three-dimensional constraints on megathrust morphology and frictional properties over large earthquake ruptures. The eastern Makran subduction zone is characterized by the subduction of the Little Murray Ridge and a strong segmentation in seismicity and large earthquake ruptures. By integrating 6,200 km of 2D seismic profiles and 50-m-resolution multibeam bathymetry with the critical wedge theory, we show that the ridge subduction has locally developed a rough plate interface, characterized by high apparent basal friction ${\mu }_b^{\prime }$ (0.09–0.14), and significant yield stress variations, while the non-ridge segment exhibits a smooth plate interface, low ${\mu }_b^{\prime }$ (0.06), and less yield stress variation. These distinct structural and mechanical properties effectively controlled the rupture behavior of the 1945 Mw 8.1 and 2017 Mw 6.3 earthquakes, which were both facilitated by the smooth plate interface, but halted upon encountering the rough segment. Moreover, the 1945 Mw 8.1 earthquake nucleated at a basement high front, where the ${\mu }_b^{\prime }$ is elevated. This nucleation location, combined with the earthquakes rupture behavior, suggests that subducted topography can act as both an asperity and a barrier. To the best of our knowledge, the 1945 Mw 8.1 event is likely the largest instrumental event generated by a subducted topographic feature, contrasting with previously globally observed magnitude ∼7 events linked to rough asperities. Therefore, the earthquake potential associated with subducting topographic features has likely been underestimated in global active margins, and requires re-evaluation.