Characteristics and slope structure of the Beishan landslide group in Tianshui City

The Beishan area in Tianshui City is located in the transition zone between the mountainous area on the northern edge of the Qinling Mountains and the Loess Plateau. The solid internal and external dynamic coupling has induced large landslide groups with a zonal distribution, which seriously restricts urban planning and disaster risk prevention in Tianshui City. Based on the systematic summary of existing geological hazard data, this study used the space-sky-earth integrated survey method to identify the variations of loess thickness from west to east, typical slope structure types, and key slip-controlling strata. The seismic landslides' development characteristics, distribution rules, and geometric and kinematic features are systematically analyzed. The results show that the landslide groups in the Beishan area are concentrated along the north bank of the Jihe Valley in a zonal distribution. The landslide types are mainly mudstone landslide and loess-mudstone interface landslide, with multi-stage rotation, translation, and multi-stage sliding. The stratigraphic structure consists of the overlying Quaternary loess and the underlying lacustrine-fluvial mudstone and claystone of the Neoproterozoic Yaodian and Ganquan formations. The landslides belonging to the bedding rock slope have three typical slope structures from west to east. The loess thickness increases gradually from west to east, the elevation and apparent friction angle are lower in the east and west and higher in the middle, and the scarp height of the landslides is higher in the east and west and lower in the middle. In addition, the seismic landslides in this region have long-runout characteristics. The equivalent friction coefficients of these landslides are between 0.21 and 0.28, and the seismic landslides in the eastern and western sections have stronger movement.