Coseismic deformation and fault slip distribution inversion of the 2025 M_W7.1 Dingri, Xizang, earthquake

On January 7, 2025, an M_W7.1 earthquake struck Dingri County, Xigaze City, on the southern margin of the Qinghai–Xizang Plateau, China. The epicenter was located at the intersection between the southern segment of the Shenzha–Dingjie Rift and the South Tibetan Detachment System, a tectonically complex region characterized by active extensional deformation. The earthquake induced large-amplitude coseismic surface deformation with a highly heterogeneous spatial distribution. To clarify the seismogenic structural characteristics and fault slip distribution of this event, we conducted a systematic investigation by integrating Interferometric Synthetic Aperture Radar (InSAR) observations with seismic source mechanism and fault slip inversion methods. (1) The InSAR-derived deformation fields reveal that the coseismic deformation was dominated by a nearly north–south-trending subsidence zone, with a maximum line-of-sight (LOS) subsidence of approximately 1.4 m and a maximum uplift of about 0.9 m. The two-dimensional deformation field further indicates pronounced subsidence accompanied by westward horizontal motion on the western side of the fault, while the eastern side exhibits relative uplift and eastward motion. These deformation characteristics suggest that the earthquake rupture was primarily governed by normal faulting, with a minor strike-slip component. (2) Based on the assumption of a homogeneous elastic half-space, a single-fault model was first employed to invert the observed coseismic deformation, yielding the optimal geometric parameters for the Dengmocuo Fault, with a strike of 184.6° and a dip angle of 54°. Although this single-fault model satisfactorily explains the major deformation features in the vicinity of the main fault, significant residual deformation remains on the western side of the fault. This result indicates the inherent limitations of a single planar fault model in fully reproducing the complete spatial pattern of the observed deformation field. (3) To reasonably account for the residual deformation, a conjugate double-fault model was introduced for joint inversion. The results demonstrate that the earthquake rupture was dominated by a west-dipping main fault, accompanied by the synchronous rupture of an east-dipping, high-angle subsidiary fault. Both faults exhibit typical normal-faulting characteristics. Compared with the single-fault model, the conjugate double-fault model significantly improves the deformation fitting accuracy, particularly within incoherent zones near the subsidiary fault, and provides a more comprehensive explanation for the overall observed deformation pattern. Assuming a shear modulus of 30 GPa, the joint inversion based on the double-fault model yields a total seismic moment of approximately 3.69 × 10¹⁹ N·m, corresponding to a moment magnitude of Mw 7.03. The results indicate that the 2025 Dingri earthquake represents a typical conjugate normal-faulting rupture event within the southern Tibetan Rift system. This study highlights the important role of conjugate fault systems in strain partitioning and energy release in extensional tectonic settings and provides valuable insights into the regional deformation mechanisms and seismic hazard assessment of the southern Qinghai–Xizang Plateau.