Three-dimensional Vp, Vs, and Vp/Vs imaging of the January 7, 2025 Mw7.1 Dingri Earthquake reveals its seismogenic mechanism in southern Tibet, China

The January 7, 2025, MS 6.8 Dingri earthquake in southern Tibet occurred within the active extensional system of the southern Tibetan Plateau. Based on more than 2.9 million P- and S-wave arrivals from 12,300 local earthquakes using an artificial intelligence–based workflow, We employed double-difference seismic tomography (tomoDDMC) and high-precision relocation to image the three-dimensional Vp, Vs, and Vp/Vs structures of the Dingri source region and to obtain high-precision earthquake locations. The relocated seismicity delineates the Dengmocuo Fault (DMCF) as the primary seismogenic fault, with the mainshock hypocenter located at the transition between high- and low-velocity zones. Tomographic results reveal that the DMCF dips steeply in the upper crust and flattens at 10–12 km depth, consistent with an extensional listric fault geometry. Prominent low-Vp and low-Vp/Vs anomalies west of the fault indicate fractured, fluid-influenced felsic rocks, while the low-Vp, low-Vs, and high-Vp/Vs (~1.85) zone beneath Dengmocuo Lake reflects fluid-saturated sediments. Aftershock clusters concentrate in intermediate-Vp (5.2–6.3 km/s) regions, whereas low-velocity or high-Vp/Vs zones show sparse activity, suggesting that fluids and strong heterogeneity limit strain accumulation. These results indicate that the Dingri earthquake resulted from extensional faulting along the DMCF, modulated by upper-crustal heterogeneity and fluid–rock interactions, providing new insights into continental extension and seismogenesis in the southern Tibetan rift system.