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

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

【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NE —SW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20：17～17：4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Ⅱ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 extensive 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 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 formation 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 NE-SW tren-ding, strike of the fault zone is

N35°～45 E°, inclination NW, dip angle at 50°～70°, 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 plane; 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 segment is the strongest, the middle segment is secondary, the northe-ast segment is the weakest.