Concentrated Rupture of the 2022 Mw 6.6 Luding Earthquake Bounded by Stress and Geometry Barriers

ABSTRACT A comprehensive understanding of the earthquake rupture process and seismicity is crucial for revealing the physical mechanisms that govern fault behavior. The 2022 Mw 6.6 Luding earthquake occurred within the Xianshuihe fault system, a region where multiple geological block boundaries intersect and fault geometries remain poorly constrained. In this study, we investigate the mainshock rupture by integrating seismic and geodetic observations and analyze background and aftershock seismicity to better characterize this complex multifault system. Our results provide new insights into fault structures and their interactions. Kinematic modeling identifies three mainshock asperities, with spatial gaps filled by aftershocks and southward rupture propagation at ∼1.5 km/s. The northern rupture segment dips westward, whereas the southern segment dips eastward. The rupture was spatially concentrated (∼18 km along strike), contrasting with the broader ∼60 km aftershock zone. Seismicity delineates the boundaries of the concentrated rupture zone along the Xianshuihe fault, whereas much off-fault seismicity occurred northwest of the main fault, along shallow left-lateral strike-slip faults to the north and normal faults to the west. These patterns align with Oligocene–Miocene geologic units rotated ∼20° counter-clockwise relative to the Xianshuihe fault. North of the mainshock, seismicity outlines a deep conjugate fault intersecting the rupture near its northern termination, forming a potential stress barrier. South of the rupture, aftershocks confirm the east-dipping geometry of a branching segment, indicating a geometric barrier that limited further propagation. These findings highlight the importance of continuous seismological monitoring in complex fault systems, advancing our understanding of how heterogeneous fault properties and geological structure govern rupture dynamics and fault interactions.