Geodetic Observations Revealing Crustal Deformation and Tectonic Transition in the Northeastern Nam Co Region, Southeastern Tibetan Plateau

Summary The northeastern Nam Co region, historically impacted by significant earthquakes such as the 1951 Ms 8.0 Beng Co and 1952 Ms 7.5 Gulu events, exhibits intricate crustal deformation patterns shaped by strike-slip and extensional fault systems. This study integrates multi-source geodetic data to analyze three-dimensional deformation patterns and fault interaction. In this region, we established 16 new GNSS campaign-model observation stations. By aligning these with existing GNSS data within a unified reference frame, we obtained a high-resolution horizontal velocity field. Additionally, ascending and descending InSAR deformation velocity fields were derived utilizing Sentinel-1A data and SBAS-InSAR technology. By fusing the GNSS and InSAR velocity fields, we extracted and analyzed the three-dimensional deformation velocity field. Utilizing an enhanced back-slip dislocation model that accounts for fault dip angles, we inverted the slip behaviors of three major faults and investigated their tectonic transition patterns. The deformation field reveals distinct kinematic behaviors among these faults. Specifically, the Beng Co fault demonstrates dextral strike-slip motion, increasing from 4.8 ± 0.1 mm/yr in west to 5.4 ± 0.1 mm/yr east, accompanied by thrusting at a rate of 3.5 ± 0.1 mm/yr. Notably, the locking depths deepen eastward from 12.6 ± 0.6 km to 17.4 ± 0.8 km. In contrast, the Dong Co and northern Yadong-Gulu faults exhibit sinistral strike-slip rates of 1.0 ± 0.1 mm/yr and 4.2 ± 0.1 mm/yr, respectively, paired with maximum extensional rates of 2.0 ± 0.3 mm/yr and 5.2 ± 0.5 mm/yr. Collectively, these faults form a stable strike-slip to extension coupled system, modulating regional crustal deformation through kinematic interactions. This study quantifies a tectonic transition model, elucidating how strike-slip faulting evolves into extensional structures in central Tibetan Plateau. Our findings contribute to a deeper understanding of strain partitioning and intracontinental deformation mechanisms within the central Tibetan Plateau.