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
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摘要
2008年5月12日,汶川M8.0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2.750×107m3。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5×107m3。滑坡距映秀—北川断裂仅3.6km,位于其下盘,地震烈度达X I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。
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 2.750×107 m3 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 5×107m3 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.
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 2.750×107 m3 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 5×107m3 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.
引文
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[3]毛彦龙,胡广韬,等.地震滑坡启程剧动的机理研究及离散元模拟[J].工程地质学报,2001,9(1):74~80.MAO Yanlong,Hu Guangtao,et,al.Mechanism of Set-Out Vio-lent-Slide of Slope Mass During Earthquake And Its Simulation byUsing Discrete Element Method[J].Journal of Engineering Geolo-gy,2001,9(1):74~80.
[4]黄润秋,许强等.中国典型灾难性滑坡[C].北京:科学出版社,2008.Catastrophic rockslides in China[C].Beijing:Science Press,2008.
[5]程谦恭等.高速岩质滑坡动力学[M].成都:西南交通大学出版社,1999.Chen Qiangong.High-speed Rocky Rockslide Dynamics[M].Chengdu:Southwest Jiaotong University Press,1999.
[6]邢爱国,胡厚田,杨明.大型高速滑坡滑动过程中摩擦特性的试验研究[J].岩石力学与工程学报,2002,21(4):522~525.Xing Aiguo,Hu Houtian,Yang Ming.Testing Study on FrictionalCharacteristic of Large-Scale and High-speed Rockslide DuringSliding[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(4):522~525.
[7]刘涌江.大型高速岩质滑坡流体化理论研究[D].西南交通大学,2002.Liu Yongjiang.Study On Fluidifying Theory of Large HighspeedRockslide[J].Southwest University,2002.
[8]S.G.Evans,G.Scarascia Mugnozza,et,al.NATO Science SeriesIV.Earth and environmental sicences-Vol.49:Rockslides fromMassive Rock Slope Failure[C].UK:Springer,2006.
[9]四川省地质工程集团公司.文家沟泥石流勘查设计书[R].2008,12.Sichuan Geological Engineering Group Corporation.WenjiagouDebis Flow Survey Design Report[R].2008,12.
[10]四川省地质矿产局化探队.中华人民共和国1:5万地质图说明书[R],清平幅,H-48-17-A.1995,11.Geological map specification of the People s Republic of China(Scale:1:50000),Qingping serial Geochemical exploration bri-gade of geology&mineral resources exploration&developmentbureau of Sichuan,Nov,1995.
[11]中国地震局震害防御司编.汶川8.0级地震未校正加速度记录[R].中国强震记录汇报,12(1).北京:地震出版社,2008.Bureau of Earthquake Damage Protection of China SeismologicalAdministration,Wenchuan M8.0 Earthquake Uncorrect Accelera-tion Record[R].Report on Strong Earthquake Motion Records inChina,12(1).Beijing:Seismological Press,2008.
[12]Xiaojun Li,Zhenghua Zhou,et,al.Preliminary Analysis ofStrong—Motion Recordings from the Magnitude 8.0 Wenchuan,China,Earthquake of 12 May 2008[J].Seismological ResearchLetters,2008,79(6):844~854.
[13]USGS Earthquake Centre,2008,shakemap.http://earthquake.usgs.gov/eqcenter/shakemap/global/shake/2008ryan/#Instru-mental_Intensit
[14]祁生文,伍法权,刘春玲,丁彦慧.地震边坡稳定性的工程地质分析[J].岩土力学与工程学报,2004,23(16):2792~2797.Qi Shengwen,Wu Faquan,Liu Chunling,Ding Huiyan.Engineer-ing Geology Analysis on Stability of Slope under Earthquake[J].Chinese Journal of Rock Mechanics and Engineering,2004,23(16):2792~2797.
[15]中国地震局,2008,汶川8.0级地震烈度分布图,China Seis-mological Bureau,2008,M8.0 Wenchuan earthquake intensitymap.http://www.cea.gov.cn/manage/html/8a8587881632fa5c0116674a018300cf/_content/08_08/29/1219980517676.html
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