New Insight into the Sliding Mechanism and Post-Stability of the 2017 Xinmo Landslide in Sichuan, China

On the 24th of June 2017, a catastrophic landslide, named the Xinmo landslide, occurred in Xinmo village, Sichuan Province, China, resulting in 103 casualties. In this study, multifield investigation data, unmanned aerial vehicle (UAV) images, and Google Earth images were adopted to explore the sliding mechanism; 47 Sentinel-1A images (2017/10-2021/11) were adopted for post-stability analysis based on permanent scatterer synthetic aperture radar interferometry (PS-InSAR). The results show that the source zone was divided into two subzones by three groups of cracks of neotectonic origin. The main source zone failed first and pulled the sub-source zone (left) down, striking the lower colluvium and causing massive sliding. The sliding provoked an unstable block (on the right side), which seriously threatened the village below. During the landslide movement, an apparent particle differentiation formed, and the large, fractured rocks ran over the hump and accumulated on the left side, while the small rocks were reflected and accumulated on the right side with the old colluvium. The differentiation finally resulted in different movement forms in which the fine particles were deposited more evenly than the coarse particles. The particle differentiation further led to two different river dam types. The five-year displacement monitoring based on PS-InSAR analysis indicated that the source zone of the Xinmo landslide and the unstable block were stable after September 2018, but the rock mass along the flank of the Xinmo landslide source zone has maintained continuous deformation thus far, with velocities of ~ 3.3 mm/yr. (right) and ~ 8.8 mm/yr. (left), respectively.