BASIC CHARACTERISTICS AND PRELIMINARY MECHANISM ANALYSIS OF LARGE SCALE ROCKSLIDE-STURZSTROM AT WENJIAGOU TRIGGERED BY WENCHUAN EARTHQUAKE

 〖JP2〗On 12th May, 2008,the M80 Wenchuan Earthquake induced a rockslidesturzstrom at Wenjiagou valley in Qingping County,Mianzhu City,Sichuan Province,P. R. China. The field survey indicated that the height of rockslide source area is 455 m,the thickness is 20～30 m,and the rockslide mass that the initial volume is 2750107 m3 slipped. The rockslidemass slipped among the bedding surface,and the total motion distance is 4022 m in horizontal,and 1443 m in vertical. The rockslide mass left 5107m3 debris in the valley. The distance between rockslide source area and seismogenic fault named YingxiuBeichuan Fault,is only 36 km. The rockslide is located in the faults footwall. The earthquake intensity of rockslide source area is XI. The disaster event formed a complete chain of earthquakeinduced geohazards and killed 48 local people. The preliminary analysis showed that rockslide startup speed was very high. The process and position of the transformation of rockslide to sturzstrom is clear. The accompanied air cushion effect and front airblast effect,the sturzstrommass motion processing were complex. In this event,it is authors opinion that long duration strong earthquake is the immediate cause of very high startup speed of slipping mass. And that the mass crashed into a hill in the valley caused rockslide mass transformed into sturzstrom.