Analysis of activity intensity for landslides triggered by the Wenchuan earthquake, Sichuan Province, China

Activity intensity for swarms of landslides is a key issue in geohazard predictions and assessment at a regional scale. From reviewed literatures, little work has been carried out on the description of activity intensity and its evaluation indicator system. On May, 12, 2008, the great Wenchuan earthquake triggered numerous landslides and debris flows. To evaluate the activity intensity of coseismic landslides, a variety of regional slides, debris flows and rock falls was investigated concerning the geological characteristics, damage to property, and life loss. After the interpretation using high-resolution imagery to map landslide inventories, they were statistically analyzed within the scope of Geographical Information Systems, noting areal density. The maximum areal density was thus obtained for seismically triggered landslides. Combined analyses in these areas show that the maximum value of areal density can be described as the activity intensity of regional landslides. The activity intensity can be categorized into eight levels from zero to seven in terms of areal density of landslides. It was noted that the activity intensity for landslides in the area hit by Wenchuan earthquake was classified into Level 7, illustrating that this area was extremely damaged by these coseismic geohazards. Following this classification, the center of the highest intensity was located on the banks of the Minjiang River near the epicenter of the earthquake, and in the vicinity of a seismic fault at Hanwang Town of Mianzhu City. Meanwhile, the banks of the Jian River and the northeast river at Nanba Town in Pingwu County were classified into Level 6. It was significantly shown that the activity intensity obviously weakens from the boundary of a coseismic fault zone to its interior. Finally, causes of triggering large numbers of landslides were interpreted, and their regional distribution was analyzed for the earthquake event.