【作者】 李西双；

【导师】 刘保华； 李三忠；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2008， 博士

【摘要】 活动构造与现代地震活动有着密切的关系。海底构造活动引起的地震/海啸等灾害有着巨大的破坏性,使得地震和地质学家越来越关注它们。渤海及其邻近地区是我国大陆东部强震的多发区,500年来有记录的6级以上的地震6次;同时,又是首都圈的门户,也是我国重要的石油基地,渤海周边人口稠密,大、中和小型城市密布,因而对这一海域活动构造的研究是十分重要和迫切的。本文基于最新获得的3000多公里的单道地震资料,结合收集的钻孔、地震等资料以及已有的基础地质研究的成果,深入剖析渤海海域(40°N以南)晚第四纪以来(128 kaB.P.)活动构造的几何学、运动学特征及动力学背景,研究它们晚更新世-全新世的活动性,并探讨与渤海地区地震活动的关系。研究结果表明:(1)海域内构造凹陷处断裂相对少,构造隆起和控制次级凹陷或凸起的主断裂上方断裂密集;在庙西凹陷西侧边缘和沙垒田凸起的东侧边缘存在2个活动断裂密集区;活动褶皱(包括背斜和向斜)长轴方向以近S-N向为主;与第三系断裂体系相比较,渤海晚更新世-全新世主要活动断裂的分布格局与之基本相似,但断裂密度要远大于前者;大多数断裂为正断裂,并在60-53ka B.P.和22-10ka B.P.这两个时期活动强烈,垂向活动速率是其它阶段的2倍。(2)郯庐断裂在近地表表现出NNE向不连续分布的特征,分段性明显,以渤中2号断裂为界分成南北两段。南段最新活动时间为全新世,分成东西两支,东支断裂带宽度约4-8km,内部变形强烈,具负花状构造;西支断裂带的宽度约1.5-3km,倾向或东或西;北段最新活动时代为晚更新世末期,有一系列斜列的断裂组成。郯庐断裂晚第四纪具有右行走滑性质,但张性作用也非常明显,晚更新世-全新世各个时段的垂向活动速率都超过0.06mm/a;在60 ka B.P.左右具有较大的平均垂向活动速率0.146mm/a;近20 ka B.P.的垂向活动速率超过0.08mm/a。(3)张家口-蓬莱断裂带在渤海地区由不连续的走向一致的若干条次级断裂组成,次级断裂倾向或南或北,局部具有负花状构造;晚第四纪以来主要表现为垂向运动,最新活动时间为晚更新世末期-全新世,晚更新世-全新世平均垂向活动速率在0.032-0.124mm/a之间;在60 ka B.P.和20 ka B.P.左右具有较大的平均垂向活动速率,分别为0.110mm/a和0.124mm/a;近20 ka B.P.的垂向活动速率超过0.06mm/a。(4)NEE-EW向断裂数量极多,但浅层结构相对较为简单,断层面多为近直立,主要表现为张性断裂,最新活动时间为晚更新世末期-全新世,具有强烈的垂向运动特征,晚更新世-全新世平均垂向活动速率在0.05mm/a以上。(5)主要界面埋深和沉积厚度显示,晚第四纪渤海的沉积中心和沉降中心相一致,并表现出自西向东、自南向北的相同变化趋势。(6)总体伸展背景下叠加了不同块体之间的相互作用是渤海地区新生代构造的动力学机制;控制渤海晚第四纪浅层活动构造变形的主要因素是区域构造应力场和早期断裂的活化作用。(7)海域地震主要受NNE向的郯庐断裂带和NW向的张家口-蓬莱断裂带控制;小震主要发生于深度小于20km的地壳内。在1969年渤海7.4级地震区新发现的一个呈NE33°向延伸、长约26km、宽3km的近地表(海底下3m左右)凹陷带表明其发震构造是郯庐断裂带。更多还原

【Abstract】 Earthquakes are closely related to active structures. More and more seismologists and geologists are attracted by submarine active structures because of large damages of earthquakes and tsunami caused by them. The Bohai Sea and its adjacent area is a strong earthquake region, where 6 earthquakes more than Ms6.0 have been recorded in recent 500 years. Additionally, this area is also the doorway of capital area and the oil and gas basement and many people live here. So it is necessary and significant to understand submarine active structures in the Bohai Sea.Based on new more than 3000-km-long single seismic data and combined with collected borehole data, earthquake catalogue and geological research results published, geometrics, kinematics and dynamics of the late Pleistocene-Holocene submarine active fault are analyzed in this thesis. Activities of these structures are documented and its relationship with earthquake in the Bohai Sea is discussed. The study shows that:(1)In the Bohai Sea, the late Pleistocene-Holocene active fault in shallow strata mainly developed in uplifts and nearby boundary faults of uplifts or depressions. There are two fault compact districts, one located in the northern part of Miaoxi depression and another in the east marginal area of Shaleitian uplift. The long axis of active folds is orientated N-S. Compared to Tertiary faults system, distribution and structural framework during the late Pleistocene-Holocene is similar to it, but the density of fault is much lager than of it. Most of these faults in shallow strata are normal faults with upstanding fault planes and tectonic movements of them mainly occurred first in the stage of 65-53 ka B.P., secondly in the stage of 20-10 ka B.P.. Vertical slip rates in these two stages were twice than in other stages.(2)Tan-Lu fault with NNE-trending manifests as several discontinuous faults in the plane view and it can be divided into two segments by the Bozhong-2 fault. The southern segment, of which the last movement occurred in Holocene, includes the eastern part and the western part. The eastern part is characterized with 4-8 km in width of fracture zone, strong deformation of sediments and negative flower structures along the fault. The western part is composed of four faults and their fracture zone ranges from 1.5 to 3 km. Some oblique ranged faults compose the north segment of Tan-Lu fault. The last movement of it occurred in the late stage of late Pleistocene. Sectional architecture and faults assembly in plane view indicate that Tan-Lu fault has a right-lateral strike slip and normal slip during late Pleistocene-Holocene. The average vertical slip rate is more than 0.06mm/a and reaches the max. 0.146mm/a. Since 20 ka B.P. the value is more than 0.08m/a.(3)Zhangjiakou-Penglai fault zone with NW trending is consisted of a group of NW trending faults in the Bohai Sea. Plane surfaces of these faults dip to S or N. Negative flower structure can be found along these faults. Last movements of these faults occurred in the late stage of late Pleistocene and Holocene. Since 128 ka B.P., they mainly exhibit normal slip with vertical rate ranging from 0.032mm/a to 0.124mm/a. The large vertical slip rate occurred first around 60 ka B.P. (the value is 0.11mm/a), secondly around 20 ka B.P. (the value is 0.124mm/a). Since 20 ka B.P. the value is more than 0.06m/a.(4)Many normal faults with NEE-EW trending are revealed by seismic profiles and most of them are characterized with upstanding plane surface and normal slip. The average vertical slip rate is more than 0.05mm/a during late Pleistocene-Holocene.(5)Buried depth of several principal discontinuities and thickness of sediments show that the depositional center is consistent with subsidence center and both of them are transferred from the west to the east and from the south to the north during late Pleistocene- Holocene.(6)The geodynamic mechanism of Cenozoic tectonic movements in the Bohai Sea is regional extension and superposed interaction of several blocks in north China. The regional tectonic stress field and reactivation of early faults are main controlling factors for late Quaternary active structural deformation.(7)In the Bohai Sea, most earthquakes often take place in the middle-upper crust(less than 20 km), and controlled by Tan-Lu fault zone and Zhangjiakou-Penglai fault zone. A newfound depression beneath the seabed at 3 m depth, with NE33°trending and 26 km in length and 3 km in width, gives the new evidence to demonstrate that Tan-Lu fault is the causative fault of the 1969 M7.4 earthquake.更多还原