Landslides induced by the Wenchuan earthquake and the subsequent strong rainfall event: A case study in the Beichuan area of China

The Wenchuan earthquake on May 12, 2008 triggered massive landslides and a subsequent, strong rainfall prompted the development of new landslides as well as the reactivation of some pre-existing landslides. The highest seismic intensity zone of the Wenchuan earthquake in Beichuan, China was selected as a case study to analyze the influence of the earthquake and the subsequent, heavy rains on landslide evolution. We selected this study area (414 km2) since it was close to the coseismic surface rupture and because it suffered strong ground motion. Based on the interpretation of high-resolution aerial photographs and remote sensing imagery combined with field investigation, 40 pre-earthquake landslides and 2221 coseismic landslides were identified with total landslide areas of 2.68 km2 and 30.81 km2, respectively. There were 134 large (over 50,000 m2), co-seismic landslides that covered a surface area of 15.54 km2 and represented approximately 50.4% of the total area of the co-seismic landslides. The coseismic landslides were mainly located on the hanging wall of the causative fault and on the steep, valley sides of the Jian River and its tributaries. A strong rainfall event occurred four months after the Wenchuan earthquake and induced 969 new landslides (which covered a 6.90 km2 area) and enlarged 169 existing landslides (2.48 km2). The landslides were identified in SPOT5 images. Ultimately, we found that earthquake tremors and the subsequent rainstorm severely disturbed the surface strata, resulting in a large number of landslides.