Rotational-translational landslides in the neogene basins at the northeast margin of the Tibetan Plateau

Rotational-translational landslides are common in Neogene basins throughout the world and are of high risk to the public. To understand the mechanism of rotational-translational failure, the spatial distribution and deformation of rotational-translational landslides in the northeast of the Tibetan Plateau are investigated in this study. The spatial distribution of these landslides is dependent on the regional tectonics and geomorphology, crustal stresses, and lithological properties. The rotational-translational landslides are concentrated in the Neogene mudstone basins, and the intensities of these landslides are observed to gradually decrease from the hinterland of the plateau to the marginal basins. The bedding-parallel shear zones within the location of the rotational-translational landslides are present in the overconsolidated Neogene mudstones with high clay content. Nearly horizontal tectonic stresses and erosion cause the formation of horizontal shear stresses in the sliding masses. In this stress environment, materials with low internal friction angle (<10°) are observed to develop in the shear zones. A weak layer with high clay content and low calcium content are observed in all the bedding-parallel shear zones of rotational-translational landslides. Further, illite-montmorillonite and illite are the main clay minerals of all the shear zones with no montmorillonite. Horizontal shearing is further accelerated by increasing the pore-water pressure and creep.