汶川地震诱发文家沟巨型滑坡碎屑流基本特征及成因机制初步分析
BASIC CHARACTERISTICS AND PRELIMINARY MECHANISM ANALYSIS OF LARGE SCALE ROCKSLIDE-STURZSTROM AT WENJIAGOU TRIGGERED BY WENCHUAN EARTHQUAKE
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摘要: 2008年5月12日,汶川M80地震在四川省绵竹市清平乡文家沟内诱发一巨型滑坡。通过现场调查得知,滑坡前后缘高差455m,厚度20~30m,滑面为基岩层面,初始方量2750107m3。滑体在运动中转化为碎屑流。滑坡-碎屑流总的水平运动距离为4022m,垂直运动距离为1443m,遗留的堆积物体积达5107m3。滑坡距映秀北川断裂仅36km,位于其下盘,地震烈度达XI度。滑坡导致文家沟中48人遇害,并形成一条完整的地震次生地质灾害链。初步分析表明滑坡启动速度快,滑坡向碎屑流转化过程明显、地点明确。碎屑流运动过程复杂,伴有强烈的气垫效应和前缘气浪冲击效应。作者认为,文家沟滑坡的高启动速度是长持时强烈地震动作用的结果,与山体的猛烈碰撞是导致滑体解体并转化为碎屑流的原因。Abstract: 〖JP2〗On 12th May, 2008,the M80 Wenchuan Earthquake induced a rockslidesturzstrom 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 2750107 m3 slipped. The rockslidemass slipped among the bedding surface,and the total motion distance is 4022 m in horizontal,and 1443 m in vertical. The rockslide mass left 5107m3 debris in the valley. The distance between rockslide source area and seismogenic fault named YingxiuBeichuan Fault,is only 36 km. The rockslide is located in the faults footwall. The earthquake intensity of rockslide source area is XI. The disaster event formed a complete chain of earthquakeinduced 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 airblast effect,the sturzstrommass 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.