Fault activity of the Wenchuan earthquake in Sichuan and seismic secondary geohazards

Quick investigation and analysis were carried out in worst-hit areas of the Wenchuan earthquake to reveal the relation between the Wenchuan earthquake fault activity and secondary geohazards. The authors analyzed the relations between fault activities and ground rupture of the Longmenshan falt zone and the characteristics of development of secondary geohazards such as rock falls, landslides and debris flows in main earthquake affected areas. According to the observation, the surface deformation and destruction (including roads, farmland, buildings and slopes along the fault zone) of three fault zones of the Longmen Mountains have distinct differences and segmentation. The activity of Yingxiu-Beichuan fault is most intense, the activities of the Nanba-Guanzhuang fault, Guanxian-Anxian fault and Pingwu-Qingchuan fault come next, showing ”longitudinal differences”, and the activity of the Longmenshan fault zone weakens from south to north, showing “latitudinal segmentation”. It is evident that the difference and segmentation of earthquake fault activity controlled the development of seismic secondary geohazards such as avalanches, landslides and debris flows, i.e. the scale, distribution density and harm of secondary geohazards along the Yingxiu-Beichuan fault all exceed corresponding features of the counterparts along other faults.