Pre- and co-seismic stress loading promoted low-angle splay fault during the 2025 Mw7.1 Tingri earthquake

Major (M ≥ 7) continental normal-fault earthquakes are rare, and the potential for low-angle ( < 30°) fault slip in such events remains highly debated. The 2025 Mw 7.1 Tingri earthquake provides a pivotal case study. Here our Bayesian inversion of geodetic data reveals complex slip on a west-dipping main fault dipping at 45-55° and a synthetic, low-angle splay fault dipping at 27°. Aftershock seismicity confirms the coexistence of both steeply and shallowly dipping fault segments. Coulomb stress modeling shows the main fault slip partially loaded the splay, while stress inversion of regional historical seismicity indicates a pre-stress regime that promoted instability on the low-angle splay. This demonstrates a cascading process, enabled by the pre-stress environment and co-seismic stress transfer, which together facilitated the low-angle faulting. Our findings suggest the mechanical viability of low-angle faulting in major normal-fault earthquakes, refining models of fault activation and seismic rupture dynamics in continental extensional regions. The 2025 Tingri earthquake occurred in an extensional, low friction regime on a low-angle splay fault that had been rendered unstable by a rotation of the principle stress axes, according to an analysis of InSAR observations and aftershock catalogues