Geological and morphological study of the Daguangbao landslide triggered by the Ms. 8.0 Wenchuan earthquake, China

Abstract

Landslides are one of the most significant geomorphic processes in mountainous regions. Recently, a gigantic landslide (Daguangbao (DGB) landslide) with a volume of 1.2 × 109 m3 was triggered by the Ms. 8.0 Wenchuan earthquake, China, and has attracted widespread attention. This landslide (28°38′16.93′′ E, 104°06′02.35′′ N) is located 85 km north-northeast (NNE) of the epicenter and on the hanging wall side, 4 km away from the surface rupture zone of the earthquake. Our long-term (2008 - present) study, which includes topographic interpretation and geological and geomorphological investigations, allows us to define the geological model of the DGB landslide and estimate the initiation and traveling mechanisms. The topography was studied by using high-resolution digital elevation models. Arial images and abundant photos at different scales are used to performed geomorphological analysis. The geology in the landslide area was studied by exploratory trenches, a tunnel, and terrestrial laser scanning (TLS). The results show that the mass movement destabilized a folded slope along a deep-seated (average depth of 400 m) bedding fault developed in the dolomite of the Sinian Formation. The morphology of the landslide main scarp is characterized by steep (55–75°) and high (up to 730 m) release surfaces, resulting from the linkage of three joint sets. An excess pore-water pressure-dependent loss of shear strength at the basal layer during the earthquake is assumed to have favored landslide initiation. An internal shear running subparallel to the stratification surface is confirmed to have dominated the longitudinal mobility of the landslide and driven landslide mass thrusting to a height of 500 m on the slopes on the other side of the valley. The DGB landslide, as a transient destabilization and morphogenesis event, has largely contributed to erosion in the study area.