DISTRIBUTION OF LARGE-SCALE LANDSLIDES INDUCED BY THE WENCHUAN EARTHQUAKE

Due to its unusually strong seismic shaking,the5 12Wenchuan Earthquake in 2008 induced hundreds of large-scale landslides.This paper is based on the interpreted data about 112 landslides,each of which has a plane area greater than 50000m2. It also uses the field investigation of representative large-scale landslides. It further conducts a systematic analysis on the distribution regularities of these large-scale landslides. It is suggested that the large-scale landslides not only show the distribution rules similar to those associated with the general landslides induced by Wenchuan Earthquake,but also present unique features in the distribution as well as sliding and moving ways. The occurrences of the large-scale landslides are usually attributed to the direct seismic forces resulting from the horizontal displacements of seismic faults. The distribution rules of large-scale landslides induced by Wenchuan Earthquake can be summarized as follows: (1)distance effect: about 80% large-scale landslides are distributed within the range of 5km from the Yinxiu-Beichuan fault(i.e. ,seismic fault ruptures). The farther the distance is,the lower the number of landslides is. (2) Locked segment effect: the large-scale landslides are mainly distributed in the five concentration zones closely related with the crossing,staggering and transforming section as well as the end of NE section of the seismic fault. The most concentrated zone is Hongbai-Chaping segment,where many large-scale landslides and the two largest landslides were induced by Wenchuan Earthquake. The second concentrated zone is Nanba-Donghekou segment at the NE end of the seismic fault,where the well-known Donghekou Landslide and Woqian Landslide are located. (3)Hanging wall effect: a vast majority of large-scale landslides (70%) are located in the hanging wall of the seismic fault,showing a clearHanging wall effect. (4)Direction effect: in the valley slopes almost perpendicular to the seismic fault,the number of large scale landslides at the slopes opposing the direction of seismic source are obviously higher than those facing the direction of seismic source,showingback slope effect.Meanwhile,the sliding and moving directions of large-scale landslides have some relations with the staggering direction of the seismic fault in each section.In Qingchuan area where the main fault activity was horizontal twisting and staggering,a considerable number of large scale landslides show the features of sliding and moving along the NE direction that was the staggering direction of the seismic fault.