Investigation on the development characteristics and reactivation mechanism of the Zhama ancient landslide in Batang County, Eastern Tibetan Plateau, China

This study examines the Zhama ancient landslide, one of several large-scale ancient landslides with complex formation mechanisms and significant reactivation trends found in the Batang Fault zone of the eastern Tibetan Plateau. The Zhama landslide, located in Deda Township, Batang County, Sichuan Province, has a dustpan shape with dimensions of 1750 m in length, 710 m in width, and a height difference of 1000 m. Based on unmanned aerial vehicle light detection and ranging (UAV LiDAR), small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), optical remote sensing interpretation, field investigation, geophysical prospecting, and drilling, the study identifies two-level sliding zones, which were found at 31.4–33.4 m and 77.7–81 m in drill hole ZK1 and at 46.6–47.6 m and 80.4–93.8 m in drill hole ZK2. The volume of the landslide is estimated to be approximately 2.5 × 10⁷–3.1 × 10⁷ m³. The Zhama landslide is divided into the landslide zone of depletion (I) and the landslide zone of accumulation (II), which can be further divided into the central local stability zone (II₁) and the foot edge strong deformation zone (II₂, II₃). The surface deformation rate of the strong deformation zone (II₂) at the foot edge of the Zhama ancient landslide is approximately − 65.8 mm/a. The reactivation of the landslide is influenced by heavy rainfall, earthquakes, fault activities, river erosion, and loading on the head edge of the landslide. Numerical simulations suggest that under heavy rain and seismic activities conditions, the head edge of the landslide deforms greatly, causing the middle and front slope to push and form a push-type landslide. Overall, this study sheds light on the development characteristics and reactivation mechanism of the Zhama ancient landslide, providing valuable insights into the hazards posed by large-scale ancient landslides in the Batang Fault zone.