地质构造对汶川大地震山地灾害发育的影响
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摘要
通过对汶川大地震灾区的调查和遥感解译,在GIS平台上对4945个灾害点进行统计,分析了山地灾害与地震烈度、距中央断裂带距离、岩性等地质构造因素的关系,研究了地震条件下地质构造对山地灾害发育的影响。结果表明:(1)地震能量主要沿中央断裂带释放,在短轴方向上能量衰减很快,灾害密度在距中央断裂0～12km范围内较大,然后锐减,灾害点呈条带状分布与中央断裂走向一致。中央断裂带逆冲走滑造成其上盘灾害发育明显高于下盘,而前山断裂带逆冲走滑与中央断裂的影响叠加造成中央断裂下盘灾害发育密度呈先降低后升高再降低的变化特点。(2)灾害总数的99.29%集中分布在地震烈度Ⅶ度及其以上地区,中央断裂带两侧高地震烈度的Ⅺ和Ⅹ区灾害不仅数量多,密度大,而且灾害规模也大,反映地震能量在形成灾害方面具有重要作用。(3)灾害密度顺序为:硬岩岩层>偶滑岩层>易滑岩层>较易滑岩层,当软硬岩层相间时,特别是硬岩在上时,在地震波的作用下容易发生开裂、崩塌和滑坡,且分别在硬质岩层和软弱岩层中较为发育。
4 945 earthquake-induced mountain hazards in Wenchuan Earthquake were identified by field investigation and interpretation of remote-sensing images.GIS techniques were used to finish the statistical data analysis for the relationship between distribution of mountain hazards and environmental factors,including distance from middle faults,seismic intensity,and lithology.Research on the geological structure effects on the development of mountain hazards in earthquake was then conducted.The main results are summarized as follows:(1)The zonal distribution of mountain hazards was consistent with strike of middle faults and seismic energy was mainly released along the middle faults which caused the attenuation of energy obvious in the minor axis perpendicular to middle faults.The high density of hazards was distributed within the distance 12 km from middle faults.The density in hangingwalls of middle faults was obviously higher than that in footwalls because the middle faults belong to reversed thrust faults.The density appeared as reduction-increase-reduction in the footwalls of middle faults because of the combined action of middle faults and front faults which both belong to reversed thrust faults.(2)The mountain hazards,well developed at Ⅺ and Ⅹ seismic intensities,were obviously responsive with seismic energy,and about 99.29% of the mountain hazards were distributed in the areas where seismic intensity was greater than Ⅶ.(3)The density appeared in the order of calculous rock>solid rock>loose rock>soft rock.Calculous rock was easy to disintegrate,especially the alternative distribution of calculous rock and soft rock by the effect of seismic wave.Many collapses were well developed in calculous rocks and landslides were well developed in loose rocks.
4 945 earthquake-induced mountain hazards in Wenchuan Earthquake were identified by field investigation and interpretation of remote-sensing images.GIS techniques were used to finish the statistical data analysis for the relationship between distribution of mountain hazards and environmental factors,including distance from middle faults,seismic intensity,and lithology.Research on the geological structure effects on the development of mountain hazards in earthquake was then conducted.The main results are summarized as follows:(1)The zonal distribution of mountain hazards was consistent with strike of middle faults and seismic energy was mainly released along the middle faults which caused the attenuation of energy obvious in the minor axis perpendicular to middle faults.The high density of hazards was distributed within the distance 12 km from middle faults.The density in hangingwalls of middle faults was obviously higher than that in footwalls because the middle faults belong to reversed thrust faults.The density appeared as reduction-increase-reduction in the footwalls of middle faults because of the combined action of middle faults and front faults which both belong to reversed thrust faults.(2)The mountain hazards,well developed at Ⅺ and Ⅹ seismic intensities,were obviously responsive with seismic energy,and about 99.29% of the mountain hazards were distributed in the areas where seismic intensity was greater than Ⅶ.(3)The density appeared in the order of calculous rock>solid rock>loose rock>soft rock.Calculous rock was easy to disintegrate,especially the alternative distribution of calculous rock and soft rock by the effect of seismic wave.Many collapses were well developed in calculous rocks and landslides were well developed in loose rocks.
引文
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[13]孔纪名,阿发友,吴文平.汶川地震滑坡类型及典型实例分析[J].水土保持学报,2009,23(6):66-70.
[14]黄润秋,裴向军,李天斌.汶川地震触发大光包巨型滑坡基本特征及形成机理分析[J].工程地质学报,2008,16(6):730-741.
[2]Keefer D V.Statistical analysis of an earthquake-in-duced landslide distribution:The1989Loma Prieta,Cali-fornia event[J].Engineering Geology,2000,58(3/4):231-249.
[3]Romeo R.Seismically induced landslide displacements:Apredictive model[J].Engineering Geology,2000,58(3/4):337-351.
[4]Papadopoulos G A,Plessa A.Magnitude-distance rela-tions for earthquake-inducedlandslidein Greece[J].En-gineering Geology,2000,58(3/4):377-386.
[5]孔纪名.滑坡稳定性判别的非计算方法[J].山地学报,2001,19(5):446-451.
[6]黄建梁,王威中,薛宏交.坡体地震稳定性的动态分析[J].地震工程与工程震动,1997,17(4):113-122.
[7]辛鸿博,王余庆.岩土边坡地震崩滑及其初判准则[J].岩土工程学报,1999,21(5):591-594.
[8]Zhou B G,Zhang Y M.Some characteristics of earth-quake-induced landslide in southwestern China[J].Northwestern Seismological Journal,1994,16(1):95-103.
[9]陈运泰.汶川特大地震的震级和断层长度[J].科技导报,2008,26(10):26-27.
[10]李勇,周荣军,董顺利.汶川地震的地表破裂与逆冲:走滑作用[J].成都理工大学学报:自然科学版,2008,35(4):404-412.
[11]Abrahamson N A,Somerville P G.Effects of the hanging wall and footwall on ground motions recorded during the Northridge earthquake[J].Bull Seism Soc.Amer.,1996,86(1B):S93-S99.
[12]俞言祥,高孟潭.台湾集集地震近场地震动的上盘效应[J].地震学报,2001,23(6):615-621.
[13]孔纪名,阿发友,吴文平.汶川地震滑坡类型及典型实例分析[J].水土保持学报,2009,23(6):66-70.
[14]黄润秋,裴向军,李天斌.汶川地震触发大光包巨型滑坡基本特征及形成机理分析[J].工程地质学报,2008,16(6):730-741.
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