The 2025 𝑀𝑤 7.1 Tingri (South Tibet) Earthquake: Rupture of Normal Conjugate Optimally Oriented Faults, Shallow Coseismic Slip Deficit, and Early Afterslip

On 7 January 2025, a magnitude 7.1 earthquake struck Tingri County at the south of the Tibetan Plateau, China, producing widespread damage in the Lhatse-Sa'gya-Tingri region and adjacent areas. The earthquake ruptured a pair of conjugate north-south striking normal faults in the Dengmecuo graben, and was the largest normal earthquake instrumentally recorded in the region. We use Interferometric Synthetic Aperture (InSAR) observations from Sentinel-1A, ALOS-2, and Lutan-1 satellites to investigate coseismic and early postseismic deformation due to the 2025 Tingri earthquake. We invert line of sight (LOS) displacements and pixel offsets for the fault geometry and slip distribution using an iterative scheme that incorporates a 3-D curved fault geometry and layered rigidity structure constrained by seismic tomography. The ruptured faults are modeled using a triangular mesh with a linear variation in slip between the nodes. The preferred model suggests average dip angles of 60-70$^\circ$ for both the main (west-dipping) rupture, and the subsidiary (east-dipping) conjugate fault, indicating optimal fault orientations consistent with Byerlee's law and coefficient of friction of 0.6-0.7. The best-fit model has a variance reduction of 91\%, and an equivalent moment magnitude of 7.0. The modeled coseismic slip exhibits a large ($\sim$60\%) shallow slip deficit, only a small fraction of which is relieved by shallow afterslip in the first $\sim$8 months following the earthquake. The observed coseismic and postseismic deformation suggest velocity-strengthening friction, as well as extensive off-fault damage in the top several kilometers of the Earth's crust. Contributions from the early viscoelastic and poroelastic relaxation are found to be negligible. Continued geodetic observations will help quantify the evolving roles of afterslip and viscoelastic relaxation, provide tighter constraints on the effective rheology of the lower crust, and illuminate the mechanisms of the ongoing E--W extension in the Southern Tibetan Rift Zone.