Kinematic and Mechanical Heterogeneity Along the Xianshuihe Fault Zone from Nine Years of Continuous Seismicity and a Crustal Velocity Model

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Abstract
The Xianshuihe fault zone (XSHF), a major strike-slip system on the southeastern Tibetan Plateau, is one of the most seismically active structures in China. However, the relationship between its kinematics and long-term seismic behavior remains poorly understood. Here, we utilize continuous seismic data from 2014 to 2022, employing machine learning to detect 12,534 events, and invert for a regional 3D velocity model. We further derive a fault locking model from Global Navigation Satellite System data and systematically analyze spatiotemporal seismicity patterns and statistical features. Results reveal pronounced segmentation in seismicity along the northern XSHF. Along with low b values and a southward shallowing of seismogenic depths, locking constraints delineate two primary zones of enhanced locking north of the Bamei region, which are embedded within a northern fault segment that remains predominantly locked as a whole. In the Bamei–Kangding segment, a releasing bend concentrates seismicity along the western and southeastern faults, with marked spatial variations in b values. Velocity and resistivity structures indicate that the extensional environment of pull-apart basins facilitates deep melt upwelling. Overall, the northern XSHF is progressively entering a locked state, with potential for Mw 6.8+ earthquakes, whereas the Kangding segment structural assemblage modulates regional compressive and strike-slip stress loading. These constraints help clarify aspects of seismic behavior and deformation in intracontinental block-margin strike-slip systems and may inform regional seismic hazard assessment.

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