Potential failure mechanism and movement process of an ancient river-damming landslide in the SE Qinghai-Tibet Plateau

Large ancient landslides are widely distributed in the Jinsha River suture zone of the SE Qinghai-Tibet Plateau. Understanding how these landslides were triggered and moved is important for future landslide risk management. Here, a detailed investigation of an ancient river-damming landslide in this zone is conducted. Field survey suggests that the deep-seated landslide developed in a scarp rock slope composed of Mesoproterozoic gneiss and Paleozoic hornblende schist. The debris volume of the landslide is estimated to be 3.3 x 107 m3. Evidence of a landslide damming event, including dam remnants and upstream lacustrine sediments, has been well preserved. Optically stimulated luminescence dating shows the landslide formed at about 5.4 ka BP. The geological setting, frequent seismic activity, and characteristics of the landslide source area suggest that the landslide was most likely triggered by a strong earthquake. The movement process of the landslide under seismic shaking is simulated using the discrete element method, with the novelty of applying a viscoelastic boundary to the model to avoid seismic wave reflection at the slope base. The simulation results show that the progressive failure process of the landslide lasts 120 s, and could be divided into three stages: (1) rupture of the rock mass at t = 0-10 s, (2) formation of a sliding surface at t = 10-20 s, and (3) rapid movement of the landslide body with a maximum movement rate of 34 m/s and blockage of the river at t = 20-120 s. This study could provide guidance for understanding the dynamic process of ancient landslides in the Qinghai-Tibet Plateau.