Characteristics of earthquake- and rain-induced landslides near the epicenter of Wenchuan earthquake

Numerous landslides were triggered by the 12 May 2008 Wenchuan earthquake in China, particularly near the epicenter. During the rainy season in 2010 after the earthquake, much of the landslide debris was reactivated, causing a large number of fatalities. The earthquake has a significant impact on the subsequent rain-induced landslides. Based on interpretation of satellite images taken in 2008 and 2010, combined with yearly field investigations, this paper attempts to (1) map the earthquake-induced landslides near the epicenter; (2) present the distribution of the landslides occurring during a subsequent extreme storm in the same area; and (3) compare the distribution characteristics of the earthquake-induced landslides and the rain-induced landslides. Through this study, the following findings were obtained: (1) the internal relief of the landslides in the study area is much higher than that in other affected regions of the Wenchuan earthquake zone; (2) the landslide area in hard rocks (i.e. the granite and diorite zones) is much larger than that in alluvium; (3) the volume of hill-slope loose deposits decreased while the volume of channel deposits increased during the process of mass transportation caused by rainfall after the earthquake; (4) during the rainy seasons after the earthquake, the density of landslides increased while the area of landslides decreased significantly and the type of landslides transformed from debris slides to debris flows; and (5) the rain-induced landslides are less steeper than the earthquake-induced landslides.