Co- and postseismic slip characteristics of the 2025 <italic>M</italic>_W 7.1 Dingri Earthquake and present-day extensional deformation of the Southern Tibetan Rift System

The seven north–south–trending rift systems distributed east-west across southern Tibetan constitute the most prominent extensional structures and are also the primary zones of strong seismic activity in the region. On January 7, 2025, an MW 7.1 earthquake struck the southern segment of the Shenzha-Dingjie Rift near Dingri County, marking one of the largest seismic events in the region over the past century. However, the seismogenic structures and earthquake mechanisms in this region remain poorly understood, highlighting the need for further investigation. In this study, we first analyzed high-resolution interseismic horizontal velocity and strain rate fields across southern Tibetan using Sentinel-1 InSAR (spanning 2015-2022) and GNSS data. Significant extensional deformation and strain accumulation were identified along several rift systems, including the Shenzha-Dingjie, Tangra Yum Co, Lunggar, Cona Oiga, and Yadong-Gulu rifts, indicating ongoing extensional tectonics and elevated seismic potential. Focusing on the 2025 MW 7.1 Dingri earthquake, we combined multi-track InSAR line-of-sight (LOS) and pixel offset tracking (POT) coseismic displacement fields to construct a two-fault geometric model and invert the coseismic slip distributions of the main and secondary faults. The results show that the main fault rupture was concentrated at shallow depths of 2 ~ 12 km with a maximum slip of ~ 4 m, while the secondary fault rupture was confined to depths of 2 ~ 7 km with a maximum slip of ~ 0.8 m. The rupture lengths of the main and secondary faults were approximately 50 km and 15 km, respectively, with only partial surface rupture, consistent with field observations. InSAR observations within 21 days after the earthquake reveal that postseismic afterslip on the main fault was concentrated in shallower regions corresponding to areas of lower coseismic slip, exhibiting spatial complementarity. Although the coseismic slip magnitudes differ significantly, the postseismic slip amplitudes of the main and secondary faults are comparable. Combined with interseismic locking inversion results, we infer that the secondary fault has distinct frictional and coupling properties from the main fault and may be in a long-term weakly locked state. Overall, the northern segments of the southern Tibetan Rift System exhibit higher regional extensional rates and stronger fault locking than the southern segments, suggesting greater strain accumulation and higher seismogenic potential in the Yadong-Gulu, Cona Oiga, Tangra Yum Co, and Lunggar rifts.