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1、 龙门山前山断裂带论文：龙门山前山断裂带地震工程地质龙门山前山断裂带论文：龙门山前山断裂带地震工程地质特征研究特征研究【中文摘要】在广泛收集基础地质资料的基础上,以龙门山前山断裂带为研究对象,从其所处的区域地质背景入手,通过野外地质调查,并结合室内试验及前人的研究成果,对其基本构造及活动性特征进行了综合分析与系统研究。在此基础上,查明了汶川地震因前山断裂引起的地表破裂特征；揭示了活动断裂对地震和次生地质灾害的控制作用；探讨了活动断裂的地质灾害效应以及地质灾害链的形成机理；开展了以北川县城新址作为典型场地的工程地质稳定性评价。通过上述研究,取得了以下主要认识：(1)龙门山前山断裂带总体呈NESW
2、 向展布,走向 N35-45E,倾向 NW,倾角 50-70,由北东段江油广元断裂、中段灌县江油断裂和南西段大川双石断裂等斜列而成。在平面上不同分支断裂大致平行排列；在剖面上构成叠瓦状构造；在走向上呈现分段性的特征。(2)龙门山前山断裂带活动性具有明显不均匀性和分段性的特征。总体表现为：南西段最强,中段次之,北东段最弱。通过对各段活动性的分析和研究,结果表明前山断裂自晚第四纪以来活动强烈。尤其在 5.12 汶川地震时,其活动性表现得更为显著,由南向北依次表现为：泸定双石段较明显；双石灌县段不明显；灌县江油段明显；江油广元段较不明显。(3)汶川 Ms8.0 级地震致其产生长约 72km 的单侧多
3、点型地表破裂带。野外地质调查表明,此次地震地表破裂的表现样式以地表破裂和褶皱挠曲两大类型为主。典型地段地表破裂分析表明,前山断裂北西盘相对上冲,具典型的逆冲推覆构造特征,且具有右行走滑运动的脆性破裂特征。(4)前山断裂带地震地表破裂位移量统计分析表明,平均垂直位移为 1.25m,最大可达 3.6m；平均水平位移为 1.05m,最大可达1.7m。垂直位移与水平位移之比在 20：1717：4 之间,其平均比值约为 2.7：1,由此说明了该地表破裂带存在逆冲运动分量和右旋走滑运动分量,且逆冲运动分量大于右旋走滑运动分量,故其以逆冲作用为主,右旋走滑作用为辅,显示了以逆冲和缩短作用为主的地震地表破裂性
4、质。(5)汶川大地震诱发的地质灾害在区域空间分布上,具有沿龙门山断裂带和河流水系呈带状或线状分布的特征,并且表现出明显的上下盘效应及灾害链效应。典型地质灾害研究表明,活动断裂是地质灾害形成的主控因素,地震是其形成的触发因素,地质环境条件是其形成的重要因素。(6)北川县城新址场地区域稳定性较好,属于类建筑场地。其中,危岩区及采空区属于稳定性差区,面积0.3 km2,占 4.93%；隐伏岩溶区属于稳定性较差区,面积 0.16 km2,占 2.60%；其他区域属稳定区,面积 5.69 km2,占 92.47%。因此,该场地总体表现为稳定。图表参考文献【英文摘要】Based on the extens
5、ive collection of basic geological materials, regarding the front-range fault zone of the Longmen Mountain as research object, the characteristics of the basic structure and activity are carried out with the indoor test and previous research results by the field geological investigation, embarked on
6、 the regional geological back-ground where it is. On this basis, the characteristics of surface rupture induced by the front-range fault are found out after the Wenchuan Earthquake; control action of the earthquake and geohazards by active faults is revealed; geohazard effect of active faul-ts and f
7、ormation mechanism of geohazard chain are discussed; engineering geological stability evaluation is done by the Beichuan County resite as a typical site. The main knowledge which is obtained by means of research above is as follows:(1) The front-range fault zone of the Longmen Mountain is generally
8、NE-SW tren-ding, strike of the fault zone is N3545 E, inclination NW, dip angle at 5070, it is composed of three segments (Northeastern Jiangyou-Guangyuan Fault, Middle Guanxian-Jiangyou Fault and Southwestern Dachuan-Shuangshi Fault). Different bran-ch faults are roughly parallel arranged in the pl
9、ane; they form imbricate structure in the section; the characteristics of segmentation is taking on in the strike.(2) The characteristics of inhomogeneity and segmentation is obviously showed al-ong the front-range fault of the Longmen Mountain. Overall performance of the activi-ty:the southwest seg
10、ment is the strongest, the middle segment is secondary, the northe-ast segment is the weakest. There had been strong activity since the Late Quaternary along the front-range fault. Especially, its activity is far more significant in the 5.12 Wenchuan Earthquake, it is orderly showed that the Luding-
11、shuangshi segment is relat-ively obvious; the Shuangshi-guanxian segment is not obvious; the Guanxian-jiangyou segment is obvious; the Jiangyou-guangyuan segment is less obvious.(3) The Ms 8.0 Wenchuan Earthquake resulted in the unilateral multi-point type surface rupture zone of about 72 km in leng
12、th. The field investigation showed that the performance patterns are dominated by the two types of the surface rupture and fold-deflection. Analysis on surface rupture of the typical districts indicates that the NW plate is relatively thrusting up, with the brittle fracture characteristics of typica
13、l overthrust and dextral strike-slip movement. (4) The statistics and analysis show that in terms of the displacement of earthquake surface rupture along the front-range fault zone, the average vertical displacement is 1.25 m, up to 3.6 m; the average horizontal displacement is 1.05 m, the maximum i
14、s 1.7 m. The ratio between the vertical displacement and the horizontal displacement is from 20:17 to 17:4, and the average is about 2.7:1, it is indicated that the existence of thrust and dextral strike-slip movement in the coseismic surface rupture zone, and the fomier is more than the latter, so
15、thrust is the key role, dextral strike-slip supplemented, with the rupture nature of thrust and tectonic shortening.(5) The regional spatial distribution of the geohazards triggered by the Wenchuan Earthquake presents the zonal or linear characteristics along the fault zone of the Longmen Mountain a
16、nd river system, and they also demonstrate the upper plate/lower plate effect and the disaster chain effect. Studies on the typical geohazards show that active fault is the main controlling factor of the geohazards formation, earthquake is the trigger factor, geoenvironmental conditions is the key factor.(6) The regional stability is relatively good in the new site of Beichuan County, belonging to Classconstructio
