【作者】 闫亮；

【导师】 李勇；

【作者基本信息】 成都理工大学 ， 第四纪地质学， 2011， 博士

【摘要】 2008年5月12日发生于龙门山构造带的汶川Ms8.0级特大地震,是目前为止世界上有仪器记录的最大震级的陆内地震。地震在瞬间改变了地形地貌,并导致地貌体系以及与之相关的河流体系产生了相应的调整,同时也是对龙门山活动构造变形最精确、最完整和最原始的记录,从而为研究汶川地震的地表破裂及地表变形过程、发震模式以及龙门山强震复发周期的预测等方面提供了一个理想的研究资料和素材。地震发生后的第1天,课题组开展了国家自然科学基金应急项目《汶川特大地震地表破裂与变形特点研究》的野外调查研究工作,考察范围含盖了整个龙门山地区。在野外调查中,我们实测地表破裂数据70余组,收集整理数据资料200余组,为开展进一步的研究工作提供了良好的科研基础。本论文主要依托国家自然科学基金项目《汶川特大地震地表破裂与变形特点研究》(项目编号:40481010)和中国地质调查中心计划项目《青藏高原地震活动带基础地质综合调查综合研究》(项目编号:1212010918010),以《龙门山活动构造与汶川地震地表破裂研究》为题,在总结前人区域地质特征、区域构造演化史等研究成果的基础上,通过野外的实地调查,以龙门山地区的活动构造和汶川地震的地表破裂为研究对象,利用汶川地震地表破裂所揭示的地质现象,重点展开了汶川地震的同震地表破裂展布规律、垂直断距和水平断距的空间变化特征及其组合样式、汶川地震的发震模式探讨以及强震复发周期的估算等方面的研究工作,是对上述项目研究成果的总结与提升。(1)通过对汶川地震同震地表破裂的精确测量,本论文重点分析了汶川地震同震地表破裂的展布规律、垂直断距和水平断距的空间变化特征及其意义、破裂的变形类型、平面组合样式等。研究表明,汶川地震产生了4条具有代表性的同震地表破裂,其中,映秀—北川地表破裂和彭县—灌县地表破裂的平面展布规律基本沿袭了原先的活动断裂发育,具有逆冲兼右旋走滑的运动特征,显示为地表的高角度逆冲;同时,在小鱼洞和擂鼓地区分别出露了2条具有捩断层性质的地表破裂,显示为调节区域地壳运动的不均衡缩短,以左旋走滑为主,逆冲为辅的运动特征。(2)依据GPS及全站仪测点数据的整合,确定了上述地表破裂垂直断距和水平断距的空间变化特征,得出映秀—北川同震地表破裂在中南段主要以逆冲作用为主,在北段主要以右旋走滑运动为主;彭县—灌县地表破裂基本以逆冲和构造缩短为主,只在北东端出现少量的右旋走滑运动。在映秀—北川同震地表破裂带上分布了两个高值区和低值区,其高值区分别位于都江堰的八角庙和北川沙坝一带,证实了双断层面震源模型的反演结果。(3)基于对都江堰八角庙断层擦痕的野外实测,我们反演了汶川地震的地表破裂过程,并与由震源机制所揭示的地表破裂过程吻合。(4)在映秀—北川同震地表破裂的滑移量存在两个高值区和低值区,其分段边界可能与小鱼洞捩断层和擂鼓捩断层的出露有关,而位于白水河—茶坪一带的低值区正对应着彭县—灌县地表破裂出露的区域,可能是由于映秀—北川地表破裂在此区段的部分能量由彭县—灌县地表破裂释放了出来。(5)通过对汶川地震的地表破裂变形样式和平面结构特征的分析,总结了5种地表破裂类型和4种地表破裂的组合样式。(6)在充分认识汶川地震地表变形指示意义的基础上,分析了汶川地震所产生的构造缩短与隆升作用,通过其对汶川地震发震模式的启示作用,对汶川地震的发震模式进行了探讨性研究,并在时间层面和垂向层面上对其进行了分析。(7)在对龙门山构造带进行分段的基础上,本论文应用地震震级—标量参数经验关系式、平均强震重复间隔等计算方法对映秀—北川断裂的地震震级及强震复发周期进行了估算,大致预测了映秀—北川断裂的分段地震震级、级联破裂地震震级以及强震复发周期。得出:漩口—小鱼洞段、小鱼洞—擂鼓段以及擂鼓—石坎段发生单元特征地震的震级估值分别为7.15±0.35、7.36±0.33和7.30±0.39,发生级联破裂的地震震级估值为7.62±0.41。通过对不同估算方法的加权平均计算,估算龙门山构造带Ms8.0级地震的复发周期约为2142a;Ms7.5级地震的复发周期约为1059a;Ms7.0级地震的复发周期约为519a。同时,通过对不同学者估算的强震复发周期的比对分析,大致可预测龙门山构造带Ms8.0级地震的复发周期应介于1000-3500a左右;Ms7.5级地震的复发周期介于840-1250a左右;Ms7.0级地震的复发周期介于410-650a左右。更多还原

【Abstract】 The Wenchuan Ms8.0 earthquake of May 12th, 2008, is the largest magnitude intraplate earthquake recorded by instruments in the world, which occurred in Longmen Shan. This earthquake changed the landform, and caused the deformation of geomorphologic system and fluvial system. It is the most accurate, complete and initial record for the active tectonics of Longmen Shan.In the frist day after the Wenchuan earthquake, we carried out field survey for Longmen Shan area, relying on National Natural Science Foundation Emergency Project“Study on Surface Ruptures and Deformation of Wenchuan Earthquake”, and measured 70 sets of datas to surface ruputure caused by Wenchuan earthquake, collecting 200 sets of datas. So it will offer a good studying foundation for the active tectonics of Longmen Shan and surface ruputure of Wenchuan earthquake.This paper will rely on National Natural Science Foundation Emergency Project“Study on Surface Ruptures and Deformation of Wenchuan Earthquake”and China Geological Survey Plan Project“Study on the basic Geology of seismic Activity Belt in the eastern Margin of Tibetan Plateau”, titled as“Study on the active Tectonics of Longmen Shan and Surface Ruputure of Wenchuan Earthquake”. Based on the previous research achievements of geological background and field survey in the Longmen Shan area, taking the active tectonics of Longmen Shan and surface ruputure of Wenchuan earthquake as research objects, using the geological phenomena revealed surface ruputure of Wenchuan earthquake, this paper which is a proving for the two projects, will study on the distributing feature and plane fabric pattern of Wenchuan earthquake surface ruputure, spatial variation characteristic of displacement, seismogenic model, recurrence intervals of strong earthquakes and so on. The main research results are as follows: (1) Based on accurate measurement for the surface ruputure of Wenchuan earthquake, This paper mainly analyzes the distributing feature, spatial variation characteristic of displacement, types of deformation of Wenchuan earthquake surface ruputure and so on. research shows that there are four mainly surface ruputures of Wenchuan earthquake in Longmen Shan area, including Yingxiu-Beichuan surface ruputure, Pengxian-Guanxian surface ruputure, Xiaoyudong surface ruputure and Leigu surface ruputure. Yingxiu-Beichuan surface ruputure and Pengxian-Guanxian surface ruputure show thrust flexural belt, striking to NE45-55°, along their active faults, with high dip angle ranged form 50-70°. Yingxiu-Beichuan surface ruputure turns out to be characterized by thrust and dextral strike-slip, extending about 245 km. Pengxian-Guanxian surface ruputure shows thrust without evident slip, extending about 70-80 km. In addition, Xiaoyudong surface ruputure and Leigu surface ruputure are two tear faults in Xiaoyudong and Leigu area, having characteristics of fragile with approximately N-S striking. The two surface ruptures pattern shows that Xiaoyudong tear fault and Leigu tear fault formed by differential movement of thrusting of Longmen Shan thrust zone during the Wenchuan Earthquake, striking to N-S direction which approximately is vertical to the strike of Yingxiu-Beichuan fault and Penxian-Guanxian fault and dipped at high angles with thrust and left lateral. So the Xiaoyudong fault and Leigu fault are two tear faults, having clear characteristics with adjusting the imbalance shorten between two blocks in the Xiaoyudong and Leigu area.(2) Having measured by GPS and EDM, this four surface ruputures cut varieties of terrain units. The spatial variation characteristic of vertical and horizontal offset along this surface ruputures shows that Yingxiu-Beichuan surface ruputure turns out to be characterized by obvious segmented features, in the middle and south segments from Yingxiu to Leigu town, thrusting with little dextral strike-slip occurred, while in the north segment from Beichuan to Qingchuan, with thrust and dextral strike-slip along this segment. Pengxian-Guanxian surface ruputure shows thrusting without evident dextarel slip, while turning out to be a litile component of dextarel slip in the northern and eastern segment. There are two high displacement and two low displacement zone along the Yingxiu-Beichuan surface ruputure from SW-NE. The two high displacement zone are located in the Bajiaomiao village of Dujiangyan and Shaba village of Beichuan. And this spatial variation characteristic of displacement in Yinxiu-Beichuan fault is matched with the result of the double-listric finite-fault model. (3) According to the typical outcrop (N31°8.719’, E103°41.513’) of Yingxiu-Beichuan fault scratch in the Bajiaomiao village where is 20km far away from Dujiangyan city, we can reflect the surface rupture process of Wenchuan Earthquake. Based on the attitude variance of the two kinds of scratch in the outcrop, this result suggests that the motion characater of the causative fault is thrust and dextral strike slip, which is in agreement with the results of surface rupture process inversed by Wenchuan earthquake focal mechanism solution.(4) There are two high displacement and two low displacement area along the Yingxiu-Beichuan surface ruputure from SW-NE. And the segment boundaries beiween high displacement and low displacement zone maybe related to the Xiaoyudong tear fault and Leigu tear fault. The Baishui River-Chaping low displacement zone is corresponding to the Pengxian-Guanxian surface ruputure in the plane fabric pattern.(5) Based on the plane fabric pattern and deformation style of the surface ruptures of Wenchuan earthquake, it can be divided into four patterns and five types, including parallel thrust fault, echelon thrust fault linked by a tear fault, branching fault, the rift valley on the top and peripheral thrust along the frontal margin. And the profile pattern of the rupture is consisting of two imbricated thrust fault in the depth.(6) On the basis of studying the denotative meaning of surface ruputure of Wenchuan earthquake, we analyze the tectonic shortening and uplifting caused by Wenchuan earthquake, discussing on the seismogenic model of Wenchuan earthquake.(7) Based on studying previous research achievements in active tectonic of Longmen Shan, measuring the offset data of surface rupture of Wenchuan earthquake, and making activity segmentations to Yingxiu-Beichuan fault. This paper will use calculation methods of earthquake magnitude to assess magnitudes of the coming earthquakes in Yingxiu-Beichuan fault, and estimate the recurrence intervals of strong earthquakes for Longmen Shan. The results show the estimations of magnitudes are 7.15±0.35 in Xuankou-Xiaoyudong segmentation, 7.36±0.33 in Xiaoyudong-Leigu segmentation, 7.30±0.39 in Leigu-Shikan segmentation, 7.62±0.41 in Yingxiu-Beichuan for the coming earthquakes, and the recurrence interval of strong earthquake for Ms 8.0 is 2142a, for Ms 7.5 is 1059a, for Ms 7.0 is 519a in Longmen Shan.更多还原