【作者】 陈宇坤；

【导师】 丁国瑜； 卢演俦；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2007， 博士

【摘要】 海河断裂是张家口—渤海断裂带中段的南侧边界断裂。该断裂对于调整张家口—渤海断裂带的左旋剪切变形运动,改变区域应力应变状态,控制天津地区的新生代(或晚新生代)构造演化和中强地震的发生具有重要作用。该断裂是一条直接穿过天津市中心市区和滨海新区的晚第四纪活动断裂。研究该断裂的空间展布、几何结构特征、断裂分段、运动学与动力学特征、晚第四纪活动特征、深部构造特征及其地震危险性,无论在科学上,还是城市防震减灾实效上都具有重要意义。本文通过综合分析前人的研究成果,结合本人在“十五”城市活断层探测项目中开展的工作,对海河断裂的空间展布、几何结构特征、断裂分段、运动学与动力学及深部构造特征进行系统研究。从研究天津地区的第四纪地层,建立本地区(晚)第四纪年代地层序列入手,对海河断裂的晚第四纪活动特征进行了深入研究,在此基础上,进行断层的地震活动性和地震危险性研究。取得了以下主要认识和进展: 1、天津地区位于冀渤断块坳陷的中北部和燕山断块隆起南部,跨越了冀中坳陷、沧县隆起和黄骅坳陷等二级构造单元。在区域NEE—SWW向主压应力场作用下,NE向河北平原和NW向的张家口—渤海两组共轭剪切断裂带在天津地区交汇,共同控制了本地区的新构造变形和现今构造运动。两组方向的断裂带共同控制了区域强震的发生,区域强震和大部分中小地震发生在NE向断裂带与NW向的张家口—渤海断裂带的交汇地段,NE向断裂带控制了地震的大小和震源机制,NW向断裂带则对地震的地点和余震分布有较大的影响和控制作用。2、海河断裂走向北西,长110km,大致沿天津海河分布,沿线与沧东、天津等断裂相交汇,是一条切割黄骅坳陷、沧县隆起和冀中坳陷的区域性断裂。以沧东断裂和天津断裂为界,海河断裂可划分为三段,各段的空间分布特征、几何结构特征和深部构造特征均存在明显的差异。东段位于沧东断裂以东的塘沽区,总长50km,该段的断层型式主要以“Y”字形为主,主断层向南倾,南侧倾向相对的次级断层与北侧主断层构成“Y”字形构造型式,向下归并主断层上,形成的断裂带宽度约2km。该段可细分为两个次级段落,位于塘沽区的陆上段落长30km,海域段落长20km,二者呈左阶排列。中段位于沧东断裂与天津断裂之间,长30km,该段的断层组合型式以平行阶梯状为主,主断裂向南倾,倾角上部稍陡,下部稍缓,表现为凹面向上的铲式正断层。各分支断层在新生代地层中向上散开,各断层间距达到700～1000m,整个断裂带横向跨度最大可达到8～10km,该段以大寺断裂为界,也可细分为两个次级段落。海河断裂西段位于天津断裂以西至武清小王庄村,长30km,断层组合型式以簇状型式为主,在这种构造型式中,断裂带表现为一组倾向相背的紧凑断层带,主断层位于断裂带的中间或南侧,倾向SW,埋深较浅,次级断层倾向与主断层相同或相背,形成簇状断层带,断层间距很小,整个断裂带的宽度仅为1km左右。至断裂带的西端陈嘴附近,断裂带开始呈散开状,断裂带宽度明显增加,各分支断层沿走向比较凌乱,但优势走向方位为NNW和NW。在卫星遥感影像上呈现为分叉状的明暗条带。3、天津滨海地区黄骅坳陷和沧县隆起两个构造单元的沉积发展历史在具有一定相似性的同时,还存在较大的差异。近20万年以来,黄骅坳陷在遭受数次大规模的海侵的同时,沉积了近60m的沉积物,但在晚更新世以来,存在两个沉积间断期,分别为68.2ka～112.2ka和68ka～6.1ka。这种沉积间断是由于海平面下降造成了该地区的裸露剥蚀。距今20～78万年期间,该区主要在陆相河流、湖泊为主的沉积环境下,偶尔会发生风暴潮或海水的入侵,沉积速率相对较慢,总计沉积厚度为50多米。但在距今68～120万年期间,陆相沉积速率可能较大,沉积物厚度达100m左右。沧县隆起在近20万年以来接受的沉积物厚度不到30m,期间经历了两次海侵事件,但沉积厚度不大。在晚更新世以来存在三个沉积间断期,对应的时间分别为:92.0ka～122.2ka、41.5ka～88.7ka.和10.0ka～41.5ka。三个间断面下伏地层均是陆相沉积,缺少海相地层。在距今20～78万年期间,该区主要以陆相沉积为主,沉积速率很慢,在漫长的50～60万年期间,沉积厚度仅为20多米,说明该区长期处于裸露剥蚀或沉积间断状态。在第四纪中期到早期,沉积地层厚度也不大,说明该区仍然继承着沧县隆起的沉积发育历史。4、古地磁磁性地层学研究表明,BZ1、BZ2、TN3钻孔所代表的黄骅坳陷和沧县隆起在第四纪年代地层序列上存在较大差异,与前人在上世纪八、九十年代对天津市的钻孔地层的研究结果也存在很大的差异。根据前人研究,天津宝坻断裂以南地区的第四纪地层没有再按照构造单元进行细分,黄骅坳陷和沧县隆起的地层序列被视为一致的,即全新统底界埋深为20m左右,上更新统底界埋深70～80m,中更新统底界埋深180～210m,下更新统底界埋深则为400m。本次研究表明,二者的第四纪地层序列存在显著的差别,分别代表了第四纪不同的沉积发育历史,形成的相应沉积物的类型和厚度都明显不同,因此这两个构造单元也应当分为两个不同的沉积单元;另外,本次研究表明,黄骅坳陷中的BZ1钻孔的全新统、上更新统及中更新统底界深度分别为19m、45m、103m左右;沧县隆起上BZ2钻孔和TN3钻孔的全新统、上更新统及中更新统底界深度分别为13m、30m、56m,而作为第四纪底部的M/G界线埋深仅为162m左右,都远远浅于前人得出的相应埋藏深度。5、研究表明,海河断裂东、西段在晚第四纪以来的活动特征存在明显的差异。根据14C测年资料,海河断裂西段在36290±2680a B.P.以来有过活动,但该断层最晚活动时代不会晚于8415±115a B.P,其主要活动时代应该在更新世晚期;在塘沽地区的海河断裂东段,最新活动时代为7200±140a B.P.,已进入了全新世早中期。通过中、浅部声学地层剖面探测,获得天津塘沽地区海河断裂的上断点埋深位于河底面以下30m,钻孔勘探揭示的上断点埋深为16.4m,其最新活动时间已进入全新世。在渤海近岸海域,声学地层探测揭示海河断裂的上断点最浅距离海底为31.2m,与塘沽陆上段基本一致。浅部声学地层剖面探测方法用于内陆淡水河道的隐伏断层探测,具有分辨率高、抗干扰能力强的优势,能够清晰地反映浅部地层的细节信息。将该方法与浅层地震探测、钻孔勘探等手段结合起来,为滨海多水地区隐伏断层的探测、断层活动性的判定甚至于断层古地震学提供了便捷而又可靠的途径。6、深部构造探测与研究表明,天津地区的地壳分层结构比较明显;不同构造单元的电性和速度特征存在很大差异。华北地区的断裂有的具有独特的深部构造组合:地壳浅部存在铲状正断裂,它们是中生代末期燕山运动形成的压扭性断层,在现今构造应力场作用下,显示左旋走滑特征,浅部断层在6～8km的深度逐渐消失,没有再向下延伸;在中地壳发育有高角度以平移活动为主的深部断裂,此断裂具有由下向上发展的趋势,在下地壳以韧性变形为主,至中地壳转化为弹性变形;这些深部断裂与地壳浅部断裂汇而不交,中间往往以低速层分隔;中地壳下部或下地壳上部发育高导层或低速层,它们对下地壳的韧性变形和中地壳的弹性变形起到了解耦的作用,这些构造组合在一起,构成地震发生的深部构造条件。大部分地震发生在低速层上面的高速体内,在接近低速体的高速体边缘上地震分布尤为密集。在海河断裂的东段和西段也存在着类似的深部构造条件。7、通过对本地区孕震构造模型的数值模拟表明,地壳中有效剪应力增长最快的部位出现在平均10 km左右(8～15km)深度的高速体上部和地壳深部断层上面,该区域的有效剪应力在加载最后阶段可成为正值,说明该区域的剪应力影响要大于围压的影响,岩石就会产生剪切破裂,发生地震。华北地区的大部分中强地震发生在地下8～15km深度范围内。主要是由于8～15km深度的区域有效剪应力为正值,而在更深的深度上,由构造应力形成的最大剪应力不能克服正应力(围压)的影响,而使有效剪应力为负值,说明这些区域随深度增大,围压越大,反而处于更加稳定的状态。根据有效剪应力的计算原理,模拟计算了在海河断裂及邻近地区有效剪应力的分布。结果表明,受华北地区近年来一系列地震和断层相互作用的影响,海河断裂西段的双口以南及东段的邓善沽、大沽一带位于有效剪应力为正值的地区,具有较强的地震危险性,海河断裂中段则位于有效剪应力为负值的地区,发生地震的危险性较低。8、利用对海河断裂的构造特征、分段特征、晚第四纪活动性、断裂带地震活动特征、断层深部构造特征及震源模型的数值模拟研究结果,对海河断裂的地震危险性进行了研究,确定了海河断裂的两个中强地震危险区分别位于海河断裂东段的塘沽—大沽一带和西段武清以南一带。9、通过对天津海河断裂活动性的探测研究,摸索出一套比较适合于滨海沉积平原区隐伏断层的探测与研究方法,可为今后在类似地区开展完全深隐伏断层的探测与研究提供借鉴作用。综合以上研究和进展,本论文取得了以下几点创新性的结果:1、通过钻孔岩芯年代学与古地磁磁性地层学测试分析,对天津地区黄骅坳陷和沧县隆起两个构造单元的年代地层进行了研究,建立了天津地区第四纪的年代地层剖面,对本区第四纪内部的分层界线重新进行了划分。为今后在该区开展更深入细致的磁性地层和第四纪年代地层研究奠定了基础。2、通过深入的探测与研究,弄清了海河断裂的空间分布、几何结构、断层分段以及晚第四纪活动特征。3、对海河断裂及其邻近地区进行了系统的深部构造特征研究,首次揭示了该断裂不同区段的深部构造组合特征及其深部孕震构造背景。利用对海河断裂的构造特征、分段特征、晚第四纪活动性、断裂带地震活动特征、断层深部构造特征及震源模型的数值模拟结果,对海河断裂为了发生地震的危险区段进行了划分,为开展该断裂的地震危险性定量研究进行了新的尝试。4、通过研究探讨,摸索出一套适用于滨海沉积平原区的隐伏断层探测与活动性评价方法。特别是将浅部声学地层剖面探测技术用于内陆淡水河道的隐伏断层探测。将该方法与浅层地震探测、钻孔勘探等手段结合起来,充分利用海相地层的标志性作用,可为滨海多水地区隐伏断层的探测、断层活动性的判定以及断层古地震学研究提供了便捷而又可靠的途径。更多还原

【Abstract】 The Haihe fault is the southern boundary of the middle segment of the Zhangjiakou-Bohai Fault Zone (ZBFZ). This fault plays an important role in adjusting the left-lateral shear movement and changing regional stress and strain status of ZBFZ. Meanwhile it also controls late Cenozoic tectonic evolution and moderate earthquake activity in the Tianjin area. The Haihe fault is an active fault in late Quaternary which directly crosses the downtown area of Tianjin and the Binhai new area. It is of important significance not only in science but also in earthquake prevention and hazard reduction to study the spatial distribution, geometric features, fault segmentation, characteristics of kinematics and dynamics, active features in late Quaternary and its deep structure characteristics as well as seismic risk of the Haihe fault. Through synthetic analyses the results of precedents and combining with the author’s work in the project of urban active fault survey during the period of the ninth five-year and tenth five-year, the dissertation made a systematic research on the Haihe fault about its spatial extension, geometric feature, fault segmentation, kinematics and dynamics, characteristics of deep structure and so on. This work began with the Quaternary stratum in Tianjin and established the chronostratigraphic sequences for (late) Quaternary in the region, and then, analyzed the active features of the Haihe fault in late Quaternary profoundly. Based on the above analysis, seismic risk of the fault was studied. The new insights and progresses of this thesis are summarized below.1. Tianjin is located in the middle-northern part of the Jibo fault block depression and the southern part of the Yanshan fault block uplift. It spans several secondary tectonic units such as Jizhong depression, Cangxian swell and Huanghua depression. Due to the regional NEE-SWW trending of principal compressive stress, the NE trending Hebei Plain fault zone is intersected and conjugated sheared with the NW trending ZBFZ in the Tianjin area. Two fault zones play an important role in controlling Neotectonic movement and recent tectonic activity. They also control the occurrence of regional strong earthquakes. Regional strong shocks and most of the moderate earthquakes usually occur in the intersection place of the two fault zones. The NE trending fault zone controls the magnitude and source mechanism of the earthquakes while faults striking NW affect in large measure the locations and aftershock distribution of earthquakes.2. The Haihe fault is trending northwest and extends about 110km along the Haihe River in Tianjin. The fault intersects with the Cangdong fault, Tianjin fault and other faults in the area. It is a regional fault which crosses through the Huanghua depression, Cangxian uplift and Jizhong depression. Bounded by the Cangdong fault and Tianjin fault, the Haihe fault can be separated into three segments, of which spatial distribution characteristic, geometric structure and deep structure features are obviously different. The east segment is located east to the Cangdong fault, which stretches 50 km in a shape like letter“Y”. The Main fault of the segment dips toward south and the secondary ruptures on the south side dips toward north, intersect and combine with the main portion, forming a 2 km wide fault zone. The segment can be subdivided into two secondary parts further: land part with 30 km length and sea part with 20 km length, which are arranged in a left-step manner. The Middle segment of the fault lies between the Cangdong fault and Tianjin faults with a length of 30 km, which are arranged mainly in parallel steps. The main rupture strikes south, dipping steeply at shallow depth and becoming gently downwards. The secondary ruptures of the fault zone disperse upward in the Cenozoic stratum with a space about 700-1000m, thus the width of the whole fault zone reaches 8-10 km. This segment also can be divided into two secondary parts bounded by the Dasi fault. The west segment of the Haihe fault is located between the Tianjin fault and the Xiaowangzhuang village, Wuqing district, which is about 30 km long and stretches in a manner of cluster that display as a series compact ruptures. The SW trending main rupture with shallow buried depth lies in the middle or south side of the fault zone. Secondary ruptures dip opposite or same to the main rupture and the space between them is very small, thus the whole width of the fault zone is only about 1 km. The fault zone begins to disperse near the Chenzui village at the west end of the fault, and the width of the fault zone increases evidently. Meanwhile, their trends become disordered but the predominant trends retain NNW and NW. The fault exhibits as branched light and shade belts in satellite remote sensing images.3. The sediment development histories of the Huanghua depression and Cangxian swell in the coastal area of Tianjin have similarity as well as appreciable differences. Since 0.2 Ma BP, the Huanghua depression underwent several times of marine transgressions and formed the sediment with thickness about 60 m. Since late Pleistocene, there existed two sediment discontinuity surfaces; the ages of them are 68.2ka-112.2ka BP and 68ka -6.1ka BP, respectively. During the period of 0.2-0.78Ma BP, the sediments in the region were mainly terrestrial facies such as lake, river and some times accompanying with storm tide or marine deposit, the rate of sedimentation was relatively slow and the sediment thickness was about 50 m in total. While in the period of 0.68-1.2Ma BP, the rate of terrestrial sediment became high, related thickness reached about 100 m.Sediment thickness in the Cangxian swell is no more than 30 m in recent 0.2 Ma BP. It underwent two marine transgression events, and there developed three sediment discontinuity surfaces since late Pleistocene, which correspond to the periods of 92.0ka～122.2ka BP, 41.5ka～88.7ka BP and 10.0ka～41.5ka BP, respectively. The underlying strata of the discontinuity surfaces are all terrestrial deposit. During the period of 0.2～0.78Ma BP, sediment in the region was mainly terrestrial, of which the sediment rate was very little and related sediment thickness there was only about 20 m, indicating that the region was ever in a state of denudation in a long time or sediment discontinuity. From early to middle Quaternary, the sediment was also thin which indicates that the sediment environment did not change much.4. Research on Paleomagnetism in the region shows that the Quaternary chronostratigraphic sequences, represented by the BZ1, BZ2, and TN3 boreholes, respectively, have large differences between the Huanghua depression and Cangxian swell. There also exist large differences compared with the results of precedents. According to the previous research of other people, the standard stratum of Quaternary south to the Baodi fault was not subdivided, the stratum sequence of the Huanghua depression and Cangxian swell were considered as the same, that is, the buried depth of the low bottoms of Helocene series, upper Pleistocene series, middle and lower Pleistocene series are 20 m, 70-80 m, 180-210 m and 400 m, respectively. In this research, the author found that two chronostratigraphic sequences are obviously different, they represent two different sediment histories in Quaternary and have different sediment types and different sediment thickness, so it should be divided into two different sediment units. In addition, this work shows that in the Huanghua depression, the depth of low bottoms of Holocene series, upper and middle Pleistocene series are respectively 19 m, 45 m, 103 m, while in the Cangxian swell they are 13 m, 30 m and 56 m, respectively. Meanwhile the M/G interface which is considered as the bottom of Quaternary is only about 162 m.5. Research of this thesis also shows that late Quaternary active features of the Haihe fault vary obviously between its eastern and western segments. According to the results of 14C dating, the western segment of the Haihe fault was active since 36290±2680a B.P., but its latest active time was no later than 8415±115a B.P, so the main active period of the segment is late Pleistocene. However, the latest active age of the eastern segment of the Haihe fault is about 7200±140a B.P., implying its active age has entered into early or middle Holocene.Shallow acoustic survey reveals that upper-break point depth of the Haihe fault in Tanggu is 39.3-43.3 m below river water surface, while the borehole data shows that it is 16.4m below ground surface. So it is certain that the related active age has entered into Holocene. In the Bohai offshore, acoustic exploration result shows that the up-break point depth of the Haihe fault is 31.2 m below seabed and shallower than that in the land area, thus it is concluded that activities of the Haihe fault are strong in the east and weak in the west since late Pleistocene, and the activity in the sea area is stronger than that in the Tanggu terrestrial area.It has advantages of high resolution, high ability of resisting against interference to apply the shallow acoustic stratum survey to explore buried faults in freshwater riverway inland, which can obtain more detailed information about the shallow stratum. Combining with shallow seismic reflection survey and borehole log, the credibility of exploration results can be enhanced. 6. Deep structure detections and research results show that the crust beneath Tianjin has an obvious layered structure, with varied electronic and velocity features in different tectonic units. Some faults in North China have particular deep structure combinations: There exist shovel-shaped faults in shallow crust, which are compressive-shear faults due to the Yanshan movement in late Mesozoic and display as left-lateral slip shear faults under the recent stress field. The shallow faults do not stretch downwards below the depth of 6-8 km. In the middle crust, there exist near-vertical strike slip faults, which have the trend of developing upward. The deformation in the lower curst is ductile and then transforms into elastic deformation in middle crust. These deep vertical faults do not intersect with the shallow ones directly. They are usually separated by the layers with lower velocity. In the lower part of the middle crust or upper part of the lower crust there are high conductive (or low velocity) layers which play a role of decoupling between the ductile deformation in the lower crust and elastic deformation in the middle crust. These structures constitute the deep background of earthquakes. Earthquakes mainly occurred in high-velocity areas which are located above low-velocity layers, especially in the edge between them. Such kind of deep structural styles noted above also exists in the eastern and western segments of the Haihe fault.7. Results of numerical simulation for the seismogenic structure in the study region indicate that the portions, where the effective shear stress increases most rapidly, appear above the high-velocity part and deep vertical faults in the crust at a depth about 8～15 km. It means that the regional shear stress has already overcomes the confining pressure, rock will break and then earthquakes would occurr if the effective shear stress changes to positive in the latest load process. However, at larger depth in the crust, the confining pressure is too strong to surmount and effective shear stress retains minus, thus the crust will keep stable.According to the principle of effective shear stress, distribution of effective shear stress in the area of the Haihe fault zone and its vicinity areas is calculated by the numerical simulation method. Results show that areas with positive effective shear stress lie in the places south to the Shuangkou area which is near the western segment of the Haihe fault, and Dengshangu and Dagu areas in the eastern part of the Haihe fault. That is to say, these two places have a higher risk of strong earthquakes. Nevertheless, in the middle segment of the Haihe fault the effective shear stress keeps minus, so it maybe has lower earthquake risk.8. Based on the above analysis, seismic risk of the Haihe fault is studied and two seismic risk zones for both the Tanggu-Dagu area in the east segment of the Haihe fault and the south Wuqing area in the western segment of the Haihe fault are determined.9. Through detection and research on activity of Haihe fault, a set of approach to detect and research on buried fault in coastal area is fished out, which could be used for reference in detection and research on complete buried fault in similar area.Summarizing above statements, this work has obtained the following innovative results:1. Through chronological and paleomagnetic dating, test and analysis, chronostratigraphic of the Huanghua depression and Cangxian swell are studied. Quaternary standard stratum profile in Tianjin is established, and the boundaries of the layers within Quaternary are classified again. A new approach is provided to research magnetic strata and Quaternary chronostratigraphy profoundly in the region.2. Based on thorough survey and analysis, more information about the Haihe fault including its spatial extension, geometric structure, fault segmentation and active characteristics during late Quaternary have been acquired. Through profound and systematic analysis of the deep structure of the Haihe fault and its adjacent areas, this work reveals the deep structure features and deep seismogenic background of the fault for the first time.3. Based on the results of deep structure detections and researches, a seismogenic structure model for the Haihe fault is eatablished and applied to numerical simulation. Synthesizing all results of the research to the fault, seismic risk segments of Haihe fault are estimated, which have innovative significance in the quantitative research on seismic risks of the fault.4. Through detection and research on activity of Haihe fault, a set of approach to detect and research on buried fault in coastal area is fished out, which could be used for reference in detection and research on complete buried fault in similar area. Especially, shallow acoustic stratum surveying is applied to the practice of exploring buried faults in freshwater river way inland. Combining with shallow seismic reflection surveying and borehole log, it can provide a convenient and credible approach for exploring complete buried fault, determining fault activity and paleoearthquake research of faults in coastal area.更多还原