Formation mechanisms and evolution model of the tectonic-related ancient giant basalt landslide in Yanyuan County, China

To comprehensively investigate formation mechanisms of tectonic-related basalt landslides in the Yanyuan County in China, the Boli ancient landslide was studied. Its morphological, geomechanical, and structural features were determined to reconstruct its evolution process. Field investigations, remote sensing imagery interpretation, and topographical analyses were conducted to assess the tectonic constraints, influencing factors, and clarify the structural, geological, and geomorphological context. The inherited tectonic brittle features involving faults and joint sets determine the location, geometrical properties, and failure process of the landslide. The Maijiaping thrust fault that cuts through the landslide area was demonstrated as the major controlling factor in the landslide’s evolution. The ductile tectonic features, the sedimentary rock intercalations, created the basal sliding surface of the landslide, as it has weaker mechanical properties with hydrophilic content when compared with the surrounding hard basaltic rock mass. Thus, a landslide-prone structure formed in the basalt slope. The conceptual evolution model was divided into five geological historical stages: (1) fold movement, (2) early fault formation, (3) relief generation, (4) landslide occurrence, and (5) recent deformation. Tectonic features and the steep relief resulting from the historical tectonic activities played important internal roles in bringing the basalt slope to final catastrophic failure. The Boli ancient landslide provides a crucial case study for evaluating landslides in an active tectonic zone in which structural plane geometries, weak intercalations, high-relief, and steep topography combine to create significant mass movement during large tectonic activities.