Multi-segmented rupture, coseismically-triggered aseismic slip, and shallow rake rotation during the 2025 Mw 7.1 Tingri, South Tibet, earthquake

On January 5, 2025, the Mw 7.0 Tingri earthquake ruptured the Dingmuco fault in the Xainza-Dinggye rift, Southern Tibet. This event was the largest normal-faulting earthquake recorded in the slowly deforming Southern Tibetan rift system and is among the largest continental normal-faulting earthquakes worldwide. Understanding the mechanics of the Tingri earthquake provides a unique opportunity to understand the regional tectonics and the rupture processes of large continental normal-faulting earthquakes in evolving rift systems. 

Here, we combine space geodetic analysis and 3D dynamic rupture simulations to investigate the earthquake. Our geodetic analysis, based on near-fault 3D optical displacement measurements and a joint optical-InSAR-SAR fault slip inversion, indicates oblique normal-left-lateral slip on a west-dipping fault that steepens toward the surface, with an average slip of 1.8 m and a shallow slip deficit of 60%. Both our fault zone width estimates and our geodetic slip model show an increase in slip-obliquity toward the surface, with left-lateral slip reaching the surface more efficiently than dip-slip, a pattern consistent with shallow rake rotation. Our geodetic analysis also reveals 0.5 m of shallow normal slip on a secondary antithetic fault located 20 km west of the main fault, which did not host aftershocks.

Next, we perform 3D dynamic rupture simulations with the open-source software SeisSol, incorporating geodetically constrained main and antithetic fault geometries, heterogeneous initial stress and fast velocity-weakening rate-and-state friction. A preferred dynamic rupture scenario that reproduces the observations suggests pulse-like, subshear rupture, with a modeled average stress drop of 6.3 MPa, higher than the observationally inferred average for normal faulting earthquakes.  A strong velocity-weakening behavior at depth, characterized by a large negative stability parameter (a − b) = −0.009, transitioning to velocity-strengthening behavior in the shallowest ~2 km is required to reproduce the observed slip distribution and moment rate release. None of our dynamic rupture scenarios dynamically triggers slip on the antithetic fault. The maximum positive dynamic and static  stress changes due to rupture on the main fault occur at shallow depths of the antithetic fault, where it is expected to be governed by velocity-strengthening friction. Together with the shallow geodetically inferred slip and the absence of aftershocks, these results indicate that slip on the antithetic fault might have occurred aseismically. However, future events across the same fault system may involve deeper coseismic slip on both faults. The high stress drop and large shallow slip deficit are characteristics of rupture on an immature fault such as the Dingmuco fault. Our study demonstrates that combining geodetic analysis with dynamic rupture simulations can shed light on  the physical processes governing seismic and aseismic slip in continental rift systems.