Estimating the Contribution of Loose Deposits to Potential Landslides Over Wenchuan Earthquake Zone, China

Loose deposits may lead to catastrophic landslides and rockslides especially during or after heavy rainfall events. In this paper, we propose a method to estimate the volume and spatial distribution (VSD) of loose deposits using airborne and spaceborne optical remote sensing data and Interferometric Synthetic Aperture Radar (InSAR) coherence. The estimated VSD of coseismic loose deposits in Wenchuan, China, the epicenter of the Sichuan Earthquake, is then used to predict potential landslides. First, high-resolution digital elevation models (DEMs) and digital orthophoto map (DOM) are developed using stereo imagery collected by an unmanned aerial vehicle (UAV) over a core test site. Next, the VSD of loose deposits is determined using the UAV imagery, DEM, and a landslide inventory map developed by field surveys, and a power-law relationship between the area and volume is established. In order to determine the loose deposits of the entire study area, the InSAR coherence of PALSAR images collected before and right after the earthquake, Landsat image classification, and DEM combined with Analytical Hierarchy Process (AHP) model are integrated in a decision tree algorithm. Finally, we develop a quantitative method of determining the severity and likelihood of potential geohazards based on VSD of coseismic loose deposits and other variables including the Normalized Difference Vegetation Index (NDVI), slope gradient, elevation, and land-cover/land-use (LCLU). A total of 42 catchments area are identified as the hot spots with a very high or high possibility of potential landslides. The VSD of coseismic loose deposits over these catchments is about 92.34% and 77.96% of the total potential loose deposits area.