The geological structure and sliding mode of the slopes in the Yigong landslide source area, Tibet

The unstable slopes of BH01, BH02, and BH03 in the Yigong landslide source area in Tibet threaten the safety of major engineering facilities downstream. In order to prevent and control the disaster risk caused by the high-elevation sliding of blocks, it is urgent to analyze the geological structure of the slope in the above-mentioned source area and their deformation trends. Based on the Pleiades digital elevation model with a precision of 2 m and its topographical shadow, this paper draws up evidence from three aspects: quantitative geomorphology, geological structure, and landslide science. In addition, it is preliminarily determined that the source area of the Yigong landslide has four secondary slope units, including the cuesta in the front imbricated thrust-fault zone, the block in the thrust-fault zone, the block in the strike-slip fault zone, and the NE-trending rift zone. There are two primary control structural planes in the slope, dipping southeast and southwest, respectively. The geological survey of the line has confirmed that the above two groups of structural planes are related to thrust faults and strike-slip faults in the imbricated nappe. The NE-trending rift crosscutting the ridge may be related to the recent EW-extensional deformation of the nappe. With the above-mentioned geological structures, the slopes in the Yigong landslide source area show multi-stage and multi-phase deep sliding along the NE-trending rift zone and have the creep-tension-shear sliding mechanism with rock landslide. According to the extension depth of the tensile fractures in the source area, the BH02 block has the potential risk of accelerated slippage. Moreover, the BH03 block is also unstable.