Characteristics and genetic analysis of submarine landslides in the northern slope of the South China Sea

Abstract

Although the structural characteristics and triggering mechanisms of submarine landslides have been investigated, little attention has been paid toward the submarine landslides in canyons. In the Baiyun canyon, there are many small submarine landslides that could be an important sediment transport process of the canyons, but few have been studied. This study aims to examine the characteristics and mechanisms of submarine landslides in the Baiyun canyon on the northern continental slope of the South China Sea using multibeam depth data, acoustic sub-bottom profiles, and borehole data. The results suggest that the submarine landslides are mainly distributed in the head and side valley walls of the canyons. The surface morphology of the landslides is broken-stepped, tongued, or round, and the area of the landslides varies between 0.04 and 15.13 km2. Nevertheless, most of the landslides have an area of less than 2 km2. The scarp height of most landslides is between 20 and 40 m. Based on the internal acoustic structures of the landslides, the submarine landslides can be divided into brittle and plastic. The brittle landslides have clear landslide walls or sliding surfaces, whereas the interior of the landslides in the upper slope area of 650–740 m near the source of submarine canyon has the original stratigraphic structure. The interior of the plastic landslides is typically chaotic and has no clear landslide walls or sliding surfaces. The plastic landslides mainly occur in the head and sides of the canyon. We determined the slope stability using the software GeoSlope and concluded that the strength of the soil on the seabed slopes and the slope gradient are the main factors that control the landslides in the study area. Landslides occur when the slope gradient is greater than 9°. In addition, when the horizontal seismic load is not zero, slopes with a gradient of less than 9° are unstable. This study will be helpful in geological risk assessments and understanding of sediment transportation in the northern margin of the Northern South China Sea.