Spatial distribution analysis of landslides triggered by 2008.5.12 Wenchuan Earthquake, China

Abstract

The 2008.5.12 Wenchuan Earthquake (seismic magnitude M w 7.9 according to the USGS) triggered a great number of landslides. A spatial database of landslides is built by interpreting the remote sensing (RS) data which covers 11 counties severely damaged by the earthquake with area of about 31,686.12 km 2. The geological settings of the study area are detailed mapped including geologic structure and lithology. The digital elevation model (DEM) of the study area with resolution of 30 m × 30 m is presented to address the topographic characteristics. Correlations between the occurrence of landslides with geological settings i.e. active faults (the coseismic surface ruptures), geological unit, slope gradient, slope elevation as well as slope aspect are analyzed using spatial modeling in GIS with the aids of field investigations. It can be concluded that the distance to the causative faults and slope gradient are much more important than other factors. Landslides are clustered distributed along the causative faults of F2 and F3, and landslides incidence are dramatically decreasing with the increasing of the distance to the causative faults. The landslides incidence has an obvious increase near the active faults i.e. F1. Landslide concentration (LC, landslides/km 2) has an obvious exponent increase with slope gradient. However, LC has no obvious relationship with geological unit and slope elevation; the difference of LC value in each geological unit (each slope elevation category) maybe have been the result affected by slope gradient for each geological unit (each slope elevation category) and distance of each geological unit (each slope elevation category) to causative fault zone. Isoseismal map reflects the incidence of landslides in some degree, and LC increases dramatically with Intensity increasing, almost all landslides occurred in the region above VI degree. Statistics result also indicates that in the near field of causative faults, landslides tend to have the initial sliding direction similar to the movement of the causative faults. And preliminary study shows that landslides incidence varies in different slopes with different structure, and consequent slopes and obsequent slopes have a higher landslides incidence than other layered slopes.