Controls on the spatial distribution of landslide hazards triggered by the 2008 Wenchuan Earthquake, Sichuan Province

During large earthquakes in regions of steep topography, seismically triggered landslides are a major secondary hazard, contributing significantly to total damage tolls. On 12th May 2008, the magnitude 7.9 Wenchuan earthquake occurred along the northwest striking fault system of the Longmen Shan mountain range, on the northwest margin of the Sichuan Basin. This area sits at the edge of the Tibetan Plateau, with high relief and steep slope gradients. The rupture zone of the earthquake and its aftershocks extend for around 300km to the NE of the epicentre (30.986° N, 103.364° E). Preliminary reports suggested that tens of thousands of landslides were triggered by the event, which greatly contributed to the high death toll of over 75,000 and widespread infrastructural damage. Our investigation seeks to identify controls on the spatial distribution of landslides triggered by the Wenchuan earthquake. This kind of investigation is commonly carried out through the production of a landslide inventory map. Landslides can be clearly identified in SPOT5 and EO-1 imagery acquired following the event. However, this investigation requires that slope failures are mapped across large areas adjacent to the 300km long coseismic rupture zone. Previous studies quote large working periods of up to 100 days to map areas of similar landslide impact using satellite imagery (Liu & Wong 1999). In order to more rapidly and efficiently map large numbers of landslides, algorithms have been developed for the automated classification of slope failures, using a combination of optical imagery and topographic data. This technique offers a tool for rapid data acquisition in the regional scale geomorphological study of landslide distributions. To date around 100,000 landslides have been mapped over an area of 20,000km2. The data is used to examine the interaction of fault rupture dynamics, topography and geology on landslide failure location. Notable are large areas of highly fractured Mesoproterozoic granite, with an average 19% area affected by landsliding. Rock-type and the structurally controlled drainage network show significant control on landslide density, in combination with marked hanging-wall / foot-wall effects, and distance decay from the fault rupture (shown in Figure 1)