汶川地震石亭江地区地震地质灾害发育规律及成因机制研究
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摘要
“5.12”汶川地震,石亭江地区受灾严重,沿江两岸红白镇、金花镇均为重灾区,其中次生灾害对各种基础设施造成毁灭型打击,滑坡、崩塌、泥石流等一度阻塞石亭江。
石亭江地区左岸为金花镇,以高、中山地貌为主,沟谷纵横,深切严重,多出露三叠系砂岩、灰岩;右岸为蓥华镇、红白镇,有三条支沟,以三叠系砂岩、灰岩为主。整条江穿越山前断裂和中央断裂,历史上多次发生强震。这些灾害随地域的不同呈现多种样式和分布规律,通过实地调查发现诸多典型性滑坡和崩塌。除了发现常规型的崩塌和土体滑坡外,还调查了大型的岩质滑坡和抛射滑坡,这两种响应方式较为强烈。抛射滑坡为大型岩块在地震时挣脱母岩的锚固,向对岸做平抛或斜抛运动,滑翔至对岸谷底堵塞河道或呈碎屑流化。抛射滑坡多见于这次地震中,为一种典型的岩体动响应方式。
地震灾害分布具有规律性,平面上由石亭江下游至上游,灾害整体越发加重,在山前断裂和中央断裂区域,以断裂为中心,向两边衰减。右岸较左岸多,灾害随右岸支沟发育。垂向上灾害多发生于斜坡肩部和坡折部位,坡脚部位灾害较少;在三面临空的斜坡顶部和单薄山脊部位,灾害多发育。
地震地质灾害成因受诸多因素控制,如地质背景、高程、坡面形态、地形地貌、岩体结构等。本地区多数岩层为三叠系砂岩、灰岩等沉积岩,又处于卸荷较强烈的深切河谷,平行于坡面的结构面发育,发生较多崩塌。地震波在传播时受地形放大效应的影响,在山体上做多次反射,地震加速度在高程大的位置表现数值要大于坡脚部位,故灾害多发于坡肩和坡顶部位。发生灾害机率凸形坡大于凹形坡大于直线坡。在顺向坡上多发滑坡和滑塌式崩塌,灾害规模较逆向坡大;逆向坡易发生倾倒式破坏,形态多呈条带状。块状结构岩体较其他结构岩体稳定。根据现场调查获得的几何特征和根据经验取得岩土体力学参数,反算出地震瞬时加速度值,对比该地区最低高程灾害点的地震加速度值,求得放大倍数在1.2～2.4之间。为指导斜坡动稳定评价提供更科学的参数,对于灾后重建有重要的现实意义。
After“5.12”Wenchuan earthquake, Shiting river region got more breakout of the earthquake.Along the river sides, Hongbai town、Jinhua town are the hardest breakout. The secondary hazard attacks more distruction of various types of infrastructure. Landslides, collapse,debris flow block Shiting river at once.
There is Jinhua town at the left bank of Shiting river, mainly the alpine、mountains landscape. The valley blossoming and cutting seriously. More exposed Triassic sandstone, limestone. There are Yinghua town、Hongbai town at the right bank of Shiting river and has three bifurcation ditch. More exposed Triassic sandstone, limestone, too. The entire river through the piedmont fault and the central fault, and there has many earthquakes in history.
The area has a variety of different presentation styles and distribution, through surveying it found a number of typical landslide and collapse. In addition to find conventional soil-landslide and collapse, but investigate the large rock-slide and thrown landslide, the respond of two ways are more strongly. The thrown landslide is a large rock throw and project to the other side of the flat, glide to the other side of the valley and block the river or stream of debris after breaking out the rock anchor. Thrown landslide is more common in this earthquake, as a typical respond.
The distribution of earthquake hazard is regularity. Along Shiting river downstream to upstream, the more seriously to the hazard. To the center of fault, attenuate both sides. The right bank of hazard is more than the left bank, the hazard develops along the bifurcation ditch at right bank. Vertically the hazard occrred in the slope shoulder and slope position, the less at the bottom of slope; the more development at the crest of overhead and thin.
Seismic geological hazard causes due to many factors, for example, geological background,elevation,slope morphology,topography,rock lithology. Most rocks are Triassic sandstone and sedimentary rocks, but also locat in cutting strongly valley, develop many joints which are parallel to the slope, so there are many collapses. Seismic waves affect by topographic amplification effect propagating, and reflect many times in the mountains. Seismic acceleration by the elevation position is greater than the foot position, so hazard generally occur in the shoulder and the top of the slope. Compare the probability of disaster,it is more convex slope rather than concave slope,than linear slope. It occur many landslide and slump collapse in the layered rock slope, and the scale of layered rock slope is more large than the countertendency layered rock slope; the countertendency layered rock slope is prone to occur topping damage. Shape likes strip pattern. Blocky rock mass compared with other structures stability.
According to the investigation, get hazard of geometry and soil-rock physical parameters base on experience, inverse the seismic instantaneous acceleration, comparing the seismic acceleration of the lowest damage, solute the magnification of at 1.2～2.4. For advising and providing stability evaluation parameter scientifically. It has important practical significance for reconstruction.
石亭江地区左岸为金花镇,以高、中山地貌为主,沟谷纵横,深切严重,多出露三叠系砂岩、灰岩;右岸为蓥华镇、红白镇,有三条支沟,以三叠系砂岩、灰岩为主。整条江穿越山前断裂和中央断裂,历史上多次发生强震。这些灾害随地域的不同呈现多种样式和分布规律,通过实地调查发现诸多典型性滑坡和崩塌。除了发现常规型的崩塌和土体滑坡外,还调查了大型的岩质滑坡和抛射滑坡,这两种响应方式较为强烈。抛射滑坡为大型岩块在地震时挣脱母岩的锚固,向对岸做平抛或斜抛运动,滑翔至对岸谷底堵塞河道或呈碎屑流化。抛射滑坡多见于这次地震中,为一种典型的岩体动响应方式。
地震灾害分布具有规律性,平面上由石亭江下游至上游,灾害整体越发加重,在山前断裂和中央断裂区域,以断裂为中心,向两边衰减。右岸较左岸多,灾害随右岸支沟发育。垂向上灾害多发生于斜坡肩部和坡折部位,坡脚部位灾害较少;在三面临空的斜坡顶部和单薄山脊部位,灾害多发育。
地震地质灾害成因受诸多因素控制,如地质背景、高程、坡面形态、地形地貌、岩体结构等。本地区多数岩层为三叠系砂岩、灰岩等沉积岩,又处于卸荷较强烈的深切河谷,平行于坡面的结构面发育,发生较多崩塌。地震波在传播时受地形放大效应的影响,在山体上做多次反射,地震加速度在高程大的位置表现数值要大于坡脚部位,故灾害多发于坡肩和坡顶部位。发生灾害机率凸形坡大于凹形坡大于直线坡。在顺向坡上多发滑坡和滑塌式崩塌,灾害规模较逆向坡大;逆向坡易发生倾倒式破坏,形态多呈条带状。块状结构岩体较其他结构岩体稳定。根据现场调查获得的几何特征和根据经验取得岩土体力学参数,反算出地震瞬时加速度值,对比该地区最低高程灾害点的地震加速度值,求得放大倍数在1.2～2.4之间。为指导斜坡动稳定评价提供更科学的参数,对于灾后重建有重要的现实意义。
After“5.12”Wenchuan earthquake, Shiting river region got more breakout of the earthquake.Along the river sides, Hongbai town、Jinhua town are the hardest breakout. The secondary hazard attacks more distruction of various types of infrastructure. Landslides, collapse,debris flow block Shiting river at once.
There is Jinhua town at the left bank of Shiting river, mainly the alpine、mountains landscape. The valley blossoming and cutting seriously. More exposed Triassic sandstone, limestone. There are Yinghua town、Hongbai town at the right bank of Shiting river and has three bifurcation ditch. More exposed Triassic sandstone, limestone, too. The entire river through the piedmont fault and the central fault, and there has many earthquakes in history.
The area has a variety of different presentation styles and distribution, through surveying it found a number of typical landslide and collapse. In addition to find conventional soil-landslide and collapse, but investigate the large rock-slide and thrown landslide, the respond of two ways are more strongly. The thrown landslide is a large rock throw and project to the other side of the flat, glide to the other side of the valley and block the river or stream of debris after breaking out the rock anchor. Thrown landslide is more common in this earthquake, as a typical respond.
The distribution of earthquake hazard is regularity. Along Shiting river downstream to upstream, the more seriously to the hazard. To the center of fault, attenuate both sides. The right bank of hazard is more than the left bank, the hazard develops along the bifurcation ditch at right bank. Vertically the hazard occrred in the slope shoulder and slope position, the less at the bottom of slope; the more development at the crest of overhead and thin.
Seismic geological hazard causes due to many factors, for example, geological background,elevation,slope morphology,topography,rock lithology. Most rocks are Triassic sandstone and sedimentary rocks, but also locat in cutting strongly valley, develop many joints which are parallel to the slope, so there are many collapses. Seismic waves affect by topographic amplification effect propagating, and reflect many times in the mountains. Seismic acceleration by the elevation position is greater than the foot position, so hazard generally occur in the shoulder and the top of the slope. Compare the probability of disaster,it is more convex slope rather than concave slope,than linear slope. It occur many landslide and slump collapse in the layered rock slope, and the scale of layered rock slope is more large than the countertendency layered rock slope; the countertendency layered rock slope is prone to occur topping damage. Shape likes strip pattern. Blocky rock mass compared with other structures stability.
According to the investigation, get hazard of geometry and soil-rock physical parameters base on experience, inverse the seismic instantaneous acceleration, comparing the seismic acceleration of the lowest damage, solute the magnification of at 1.2～2.4. For advising and providing stability evaluation parameter scientifically. It has important practical significance for reconstruction.
引文
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[3]刘洪兵,朱日希,地震中地形放大效应的观测和研究进展[J].世界地震工程,1999,15(3):20-25.
[4]王涛,马寅生,龙长兴,等.四川汶川地震断裂活动和次生地质灾害浅析[J].地质通报,2008,27(11),1913-1922.
[5]肖克强,李海波,刘亚群等.地震荷载作用下顺层岩体边坡变形特征分析[J].岩土力学,2007,28(8).1557-1564.
[6]张倬元,王士天,王兰生,工程地质分析原理[M].北京:地质出版社,1994.
[7]林良俊,方成,李小杰等. 5.12汶川地震灾区地质灾害情况初步分析[J].水文地质工程地质, 2008,(4), 129-132.
[8]祁生文,伍法权,刘春玲,等.地震边坡稳定性的工程地质分析[J].岩石力学与工程学报,2004, 23(16):2792～2797.
[9]邢伟,地震冲击波对坡面位移和地面形状的影响[J].水土保持应用技术, 2007,(4):6-8.
[10]殷跃平,汶川八级地震地质灾害研究[J].工程地质学报,2008,16(4):433-444.
[11] Hartzell S H,Carver D L.King K W.Initial investigation of site and topographic effects at Robinwood.Bull.Seis.Soc.Am.1994.84:1336-1349.
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