【作者】 董绍鹏；

【导师】 韩竹军；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2009， 硕士

【摘要】 汶川Ms8.0大地震为研究地震机制提供了一个很好的窗口,震后对发震的龙门山地区的研究更是引起了全球地学科技工作者的注意。而目前对于汶川地震的研究还处于基础资料收集整理的阶段,很多问题都没有得到解决,需要更深入的研究分析。一直以来对汶川地震的发震断裂—北川-映秀断裂各方面的研究是不充分的。目前对其活动速率、活动性、强震复发周期以及震后其地震地表破裂带特征等重要的科学问题上都还没有统一的认识。本论文选择中央断裂活动特征表现较为明显的映秀镇作为主要研究对象,利用地貌分析、野外地质调查、挖槽开挖、剖面分析等技术手段,对该镇的地震地表变形带特征以及北川-映秀断裂活动习性进行初步研究。论文完成的主要内容和采用的研究方法如下:1)在地震地表破裂带表现清晰的映秀镇,通过野外实地地质调查填图并对地震地表变形特征地区利用测量工具完成精细构造地貌测量,获得了该处的地震地表破裂带特征以及变形带宽度、变形量等定量结果。2)通过地形图分析、野外实地考察等方法,选取中央断裂(北川-映秀断裂)通过的映秀镇北的中滩铺的T2阶地作为探槽开挖点。利用古地震探槽分析、光释光年代样测试确定北川-映秀断裂的古地震,分析认识该断裂的活动习性。3)对映秀镇发育良好的四级阶地分别采集年代样品并测试分析,获得各级阶地的年龄值。对剖面较好的T4阶地进行了系统采样和剖面分析。并对中滩铺清楚的四级阶地的构造陡坎进行了精细地形测量,分别获得了各级阶地的陡坎高度,结合各级阶地的年龄,获得了不同时间段中央断裂的垂直抬升速率,并做了初步分析。4)在以上工作的基础上,对中央断裂的抬升速率及其地震危险性进行了初步分析。论文获得的主要结论如下:1)映秀镇地震地表破裂沿先存断裂发育。映秀镇地表变形带主要表现为垂向运动;地震地表变形带宽度约为60m,垂直变形量为2.7m。2)断裂的垂直滑动速率在中晚更新世为0.93±0.14mm/a,晚更新世和全新世中期为0.53±0.12mm/a,全新世晚期为1.17±0.24mm/a。3)在4.93±0.86ka以来,5.12汶川地震之前,映秀镇发生过古地震事件。更多还原

【Abstract】 Ms 8.0 Wenchuan Earthquake shocked everyone, and after the earthearth, research on Longmenshan Area where the earthquake occured interested geological researchers all around the world. But now the study on Wenchuan Earthquake is still in the stage of collecting basic data, which means further study is very necessary and many issues are unsolved. All along, study on Beichuan-Yingxiu Fault which is considered as seismogenic fault of Wenchuan Earthquake is not sufficient with the representation that many scientific problems involving it, such as activity rate, activity, recurrence intervals of strong earthquakes, seismic deformation characteristic and so on is still in argument. So, Yingxiu Town where the Central Fault’s activity charactertistic behaves obviously is selected as research object in this paper. Primary study on seismic surface deformation and faulting behavior of Central Fault (Beichuan-Yingxiu Fault) is done by methods such as topographic analysis, field geological investigation, trench excavation, geological profile analysis and so on.Those below are main content of the paper and research methods that were adopted:1) Seismic surface deformation characteristic and some quantificational results such as deformation width, deformation amount in Yingxiu Town where seismic surface deformation is very obvious are obtained by field geological mapping and structural topographic surveying with the help of surveying machine.2) Terrace T2 at Zhongtanpu in the north of Yingxiu Town where Central Fault (Beichuan-Yingxiu Fault) is chosen as trench spot after topographic map analysis and field investigation. And then, paleoseismic events and faulting behavior of Beichuan-Yingxiu Fault are obtained by paleoseismic trench analysis and testing OSL samples.3) Age value of the four terraces well developed at Yingxiu Town is gotten by collecting and testing dating samples. Terrace T4 whose profile is very well is sampled and analyzed systemically. And we did fine topographic surveying at Zhongtanpu where structural scarps on four terraces, and scarp height of every terrace is obtained. Combining the age value of every terrace, we got vertical uplifting rate of Central Fault in different time scale and did primary analysis.4) On the base of work done above, primary analysis on seismic risk and uplifting rate of Central Fault is done.Main consequences of paper are below:1) Seismic surface deformation characteristic at Yingxiu Town shows us that seismic rupture plane develops along previous fault plane, which is evidence of in-suit recurrence model of earthquakes. Seismic surface deformation mainly performs vertical displacement in Yingxiu Town, the epicenter of Ms8.0 Wenchuan Earthqauke. The width of seismic surface deformation at Yingxiu Town is about 60m, uplifting amount 2.72m.2) Since 4.6±0.8ka ago, or in later Holocene, vertical uplifting rate of Beichuan-Yingxiu Fault is 1.17±0.236mm/a, while since 24.5±5.5ka ago, or in later Pleistocene and middle Holocene, the rate is 0.53±0.12mm/a. Lower limit of uplifting rate is 0.931±0.137mm/a since 46±4.6ka ago, or in middle and later Pleistocene.3) Paleoseismologic earthquake occured at Yingxiu Town between 4.93±0.86ka ago and Wenchuan Earthquake.更多还原