【作者】 许华明；

【导师】 曲国胜；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2008， 博士

【摘要】 克拉通破坏与现今强震活动的关系是现今大陆构造和动力学研究的前沿科学领域。作为现今克拉通破坏响应的克拉通内部强震具有震级大、复发周期复杂、震源浅、浅表破裂带长度和垂直位移量小以及具有对地面建筑物和设施毁灭性破坏的特点,往往造成巨大的人员伤亡。长期以来,鉴于克拉通内部强震对人类生命的严重威胁,对其成因探索一直是国际地学界的关注焦点,也是各国政府城市化和工业化建设与可持续发展极其关注的热点问题。论文着眼于冀南地区克拉通强震的发震构造,充分利用前人的研究成果,结合石油地震剖面解释和邯郸市活断层探测深部资料的综合分析,综合考虑到地层沉积特征及断层展布形态,对冀南地区克拉通的破坏过程与中新生代沉积响应、区域地震构造背景及其未来地震活动性、尤其是强震构造活动机理进行了研究。鉴于研究区构造位于平原隐伏区,本文充分将项目的探测资料与三维构造模型、三维速度模型及有限元模拟相结合进行研究,取得了一些重要的成果及认识,解决了长期困惑研究人员的太行山山前构造体系的展布问题,重建了冀南地区克拉通的破坏过程,建立了磁县地震的发震机理,丰富了板内强震的孕震模式。一、初步认识了深浅部断层特征及构造组合1、古太行山断层古太行山断层为太行山强烈隆起区与山前隆起区(丘陵地带)的分界断层,在邢台西部呈北东向展布,出露较完整。从册井北部往南过武安至磁县,地表露头断续分布,逐渐转为北北东向或近南北向。该断层断距较大,导致其上部的脆性岩层(寒武系和奥陶系灰岩)强烈拉张,为赞皇核杂岩体的主拆离断层,同时也是上地壳和中地壳之间的拆离滑脱面,坳陷内的其他控制凹陷沉积的二级断层终止于此滑脱面之上。2、太行山山前断层(元氏断层、邯郸断层、汤西断层)在研究区内,太行山山前断层称为邯郸断层,是一条重要的隆起区与坳陷区的边界断层,断层附近既是太行山重力异常变化的梯度带,也是地壳形变特征的转折带。其西部表现为重力低异常,垂直形变为正值,水平滑移速率较小;东部则正好相反。通过对宽频带深部探测成果与小震精确定位所获得的速度结构的研究,认识到邯郸断层并非控制山前凹陷沉积的主控断层,而仅仅是盆地与隆起的分界断层,倾角上陡下缓,最陡处可达70°,断面下延的最大深度在4000~5000m,由一组近平行的东倾断层组成,断层主要形成于古近纪,由东向西上断点埋深有依次变浅,形成时间由老到新的特征。在邯郸凹陷内部,邯郸断层以下存在一个小规模的地堑,往北延伸至永年以北后地堑系的一条断层逐渐与邯郸断层合并。3、磁县-大名断层磁县-大名断层是北部临清坳陷与南部内黄隆起之间的边界断层,向东偏南过朝城镇与聊兰断层相交。经对华北盆地南部隐伏区石油地质资料揭示的盆地构造、地表活断层调查及隐伏区浅层地震探测以及磁县-大名断层地震活动性分布特征,将磁县-大名断层划分为三段,东段为大名-临漳段,以隐伏断层及中强震沿断层附近断续分布为特征;中段为磁县-峰峰段,以隐伏断层和控制地貌发育为特征;西段为南山村-岔口段,以部分地区出现1830年磁县地震地表破裂带为特征,总体表现出基岩区山体和山脊被断错的地貌现象。4、曲陌断层曲陌断层西起朱庄水库以西,东经北掌乡到曲陌,全长约60km,走向290°,倾向南,倾角70-80°,控制了邯郸断陷的北部边界。该断层断错二叠-三叠系1200m左右,始新统底界断距为500m,断错新近系底界约50m。断层落差由西往东逐渐减小,呈弧形弯曲,最后归并于邯郸东断层。该断层活动性较强,在与邯郸东断层交汇处曾发生了1708年5.5级地震,研究表明曲陌断层西端是未来强震最有可能发生的区域。5、紫山西断层该断层北起邢台市西侧,向南从过沙河,经北掌,顺延紫山西侧山前,到鼓山西的伯延一带消失,全长约70km。走向北北东,倾向西,倾角较陡,该断层控制着武安盆地的发育。根据宽频带深部探测成果与小震精确定位所获得的速度结构,认识到在其下部可能存在一条深大超壳断层,从而导致中地壳小震密集分布,地表中性-偏碱性的岩浆岩发育,过曲陌断层后岩浆岩急剧减少,小震活动也明显降低,表明深部结构有所变化。6、断层体系邯郸凹陷的断层体系分为三个层次:浅表断层系(0~2km)以断层端部常发生震源深度为6km左右的小震为特征,表现为浅表脆性岩系为调节局部应变而形成的捩断层,主要有永年断层、联纺路断层和马头断层;中层断层系(0.1~9km)断层控制或影响凹陷的沉积特征,大多数断层属于此类断层;深层断层系(10~12km)为拆离断层面,凹陷内的中层断层系大多归并于此滑脱面上,即古太行山断层。总体上看,由于北东向断层发育相对较晚,常常切割北西向断层,但由于曲陌断层活动性较强,在北东向断层形成后仍有过较强活动,所以在此断层上的北东向断层被错断,并呈现出左列的特征。在山前凹陷内,主要存在三条明显的调节带,由北向南分别为:(1)隆尧调节带;(2)永年-曲陌-曲周调节带;(3)马陵调节带。二、根据沉积特征重现了中新生代构造演化早中生代的印支运动波及整个中国,形成了北东-北北东向展布的东隆西坳的构造格局。到燕山中期强烈的左行剪切挤压作用,这种构造格局得到进一步加强,东部隆起进一步抬升。在侧向挤压和深部热力作用下,岩石圈及陆壳厚度急剧增大。在太行山隆起区尤为突出,在此构造背景之下,冀南地区发育了赞皇核杂岩体。这种单个核杂岩体的出现体现了深部的热力作用;其整体的带状展布,又反映了受深部的超壳断层控制。中生代中晚期与核杂岩体有关的拆离滑覆构造,经过了古近纪裂陷伸展作用强烈的改造仍有迹可循。从构造演化角度来看,冀南地区克拉通经历了二叠纪海陆交互相、三叠纪、侏罗纪-白垩纪的河湖相、古近纪的断陷沉积、新近纪的坳陷沉积阶段,其演化过程和沉积特征反映了板块运动和深部热力作用双重影响的结果。三、合理分析了华北克拉通破坏和岩石圈减薄的机制因为板块聚合的阶段性,即华北板块与扬子板块拼合、伊佐奈岐板块俯冲和消亡和青藏高原的隆升以及太平洋-菲律宾海板块的俯冲三个时期及其各具特征的沉积构造,可以将克拉通破坏划分为三个阶段,即前破坏期(257~161Ma)、破坏孕育期(161~65Ma)及破坏期(65~0Ma)三个阶段。从克拉通破坏的沉积响应来看,破坏孕育期的地幔和中下地壳的热事件最丰富,但在晚侏罗世-白垩纪的沉积以河流相和浅湖相沉积为主;破坏期的热事件较少,但此期的沉积却表现为强烈的断陷沉积作用。前者反映了内“热”外“冷”,以中深部热交换和热侵蚀为主;后者反映了外“热”内“冷”,以浅部强烈的断陷沉积作用为主。因此根据地壳结构在中上地壳之间存在滑脱面事实,将华北克拉通破坏分为两种破坏类型并建立了不同阶段的破坏机制:1、地幔主动上隆,地壳被动伸展在核杂岩形成之前,由于前破坏期的强烈造山引起地壳原有的平衡被打破,在重力均衡作用下,地幔物质强烈上涌,在中上地壳之内形成强烈的岩浆侵入作用,主要表现为岩浆大量喷发,并在壳内形成大量低速体。上地壳在岩浆侵入的作用下弱伸展; 2、地壳主动伸展,地幔被动上隆核杂岩的形成标志华北东部进入强烈的伸展时期,地壳在伸展过程中产生了强烈的断陷作用,在强烈拉张区地壳变薄,地幔由于负载降低而被动上隆。四、合理解释了太行山重力异常梯度带根据宽频带台阵深部探测和小震精确定位的研究结果,在邯郸断层以东,地壳各界面平缓变化,不存在深大断层。根据地表发育中性-偏碱性岩浆岩以及小震精确定位的速度结构分析,在紫山西断层下部的中下地壳存在一条深大断层,因此太行山山前的重力异常梯度带是该深大断层和莫霍面下陷的双重作用结果,且以莫霍面下陷为主导作用。五、初步掌握了邯郸凹陷及邻区的地壳结构由于邯郸凹陷以平原隐伏区为主,因此结合前人的研究成果,充分利用项目探测资料,引入三维可视化建模技术,对邯郸凹陷及邻区的深部地壳结构有了初步了解。宽频带深部探测给出了邯郸凹陷内部的地壳结构,结果表明地壳内部各界面平缓变化,莫霍面表现为北高南低,东西基本平整的形态;小震精确定位的速度结构反映了紫山西断层下部存在明显的低速异常带,小震震中表现为明显的分带性,主要集中在10~22km的中地壳,上下地壳小震明显稀少。根据以上结果,从上到下,可将地壳及上地幔可以为四个构造层,即:上地壳、中地壳、下地壳和上地幔。中、下地壳速度结构比较均匀,它与地表断层系统基本无关。据此推断,上地壳与中、下地壳之间存在运动变形的解耦,中间存在一条区域解耦面,表层断层体系归并于此解耦面上。地壳内的各个界面在紫山西断层以东横向上较为均匀,未见明显的错断或突变;而往西Moho面逐渐变深,在此转折点之上的中地壳存在一条明显的深大断层,从而导致地表有幔源岩浆侵入,后遭受剥蚀出露于地表。六、基本查明了冀南地区克拉通的板内强震与发震构造间的关系任县凹陷、邯郸凹陷和丘县凹陷为临清坳陷最西部的负向单元,地处太行山隆起区和华北平原坳陷区两大构造单元的分界线上,在任县凹陷的东北角和邯郸凹陷的西南角分别发生了1966年和1830年两次大地震,而两次地震位于许多学者提出的唐山-河间-磁县地震带上,从研究结果看,在邢台与磁县之间明显有一个地震空白区。从小震震源分布来看,小震密集分布于10~20km的中地壳,正是壳内低速体分布区域。低速体上方为华北克拉通盆地的结晶基底以及早古生界脆性灰岩,在低速体端部容易形成应力集中。对于磁县-大名断层带东段,其上为巨厚的中新生代沉积,其下未有明显的低速异常体,所以局部应力集中在上地壳的伸展变形过程中会得到逐渐释放,表现为零星分布的小震或中强震;西段中新生代沉积较薄,因刚性结晶基底以及早古生界的脆性岩层的存在明显降低了伸展的速度,这可从地壳运动和构造形变特征上得到证明,从而在低速体的端部应力集中,当达到或超过结晶基底以及早古生界脆性岩层的极限破裂压力时,则产生地震。因此区内的孕震机理为:在盆地和隆起的边界,存在贯穿中下地壳的深大断层,形成上地幔物质上涌的通道,并在刚性结晶基底以及早古生界的脆性岩层下形成壳内低速体,导致局部应力集中,当达到或超过脆性岩层的极限破裂压力时,则产生强地震。七、初步建立了未来强震发震模型新近纪以来华北板块地处三大板块间的三角地带,由于印度板块与欧亚板块的碰撞,喜马拉雅山脉快速形成,青藏高原迅速隆升,致使周边老造山带重新活跃,同时西太平洋的菲律宾海板块北北西向俯冲,在北方又受到天山-兴安板块的阻挡,使冀南地区克拉通受到NEE向的挤压,整体处于一种挤压应力加强的状态。在此应力状态下,克拉通内部次级板块之间更加紧密的接触,当受到垂向力的作用时,更容易在垂向力作用区域的中地壳刚性岩层内发生破裂。根据前人的研究成果以及所获取的丰富资料,建立的冀南地区盆山结合部未来强震发震模型,同时根据有限元模拟对未来可能发生强震的区域进行了预测,结果证实在曲陌断层上盘的西部附近存在库仑应力增强区,该区域是未来强震最有可能发生的区域。根据建立的孕震模式推断认为曲陌断层上盘的西部是未来强震最有可能发生的区域,可能震级为6.0~7.0ML;按照应力加载模型推测,估计未来100年将是最可能发生的时间。总的看来,论文从研究冀南地区山前凹陷与太行山隆起之间的中新生代和现今构造特征出发,从浅部到深部对其构造特征、构造演化及与小震活动规律进行剖析,充分利用活断层探测深浅部资料,通过地表野外调查、浅层地震勘探、宽频带台阵深部探测、小震精确定位和三维可视化建模,对冀南地区克拉通深浅部构造之间的耦合关系、克拉通破坏与沉积构造响应、克拉通破坏机理和强震孕震机理做了有益的探讨,研究了该区的地壳结构特征,获得了构造与强震之间的成因机制,探讨克拉通板内地震的孕震机理,建立了冀南地区克拉通破坏与发震构造的关系模式。更多还原

【Abstract】 The North China Craton (NCC) is one of the most active continental blocks in the world, as indicated by the frequent occurrence of devastating earthquakes. The natural hazards have enormous impacts on both the economy of China and the quality of life in the region. The study on the mechanism of the hazards requires a complete knowledge of geodynamics, lithology, tectonophysics, geochemistry, seismonogy and geology as well as synthetic analysis of them.This thesis focuses on the evolution of Meso-Cenozoic sedimentary and tectonics, craton destruction, crustal thinning and seismogenic faults of the southern area of the North China Craton (SANCC) and summarizes the progress and problems in these studies of the extensional tectonics represented by metamorphic core complexes and fault depressions. Some important subjects, which merit the further study and their significance in the study of the destruction and lithospheric thinning of the NCC, were discussed.Research has been carried out in three ways, fault investigation, sedimentary analysis and numerical simulation in SANCC. Some important results have been obtained and are presented as follows.1. Characteristics of surface structures and buried structures and structural system(1) The paleo-Taihangshan faultThe paleo-Taihangshan fault is a bounding fault between The Taihangshan high uplift area and range-front uplift area (hilly terrain), which extends towards NE near the western Xintai and turns into NNE or nearly NS gradually from Cejing, passing by Wu’an, then to southern Cixian. Outcrops of the fault can be seen time and again. The fault is the main detechment fault of Zanhuang metamorphic core complexes. With large fault throw, the hanging wall was extended intensively and formed the topography with alternating trenches and ridges.(2) The Taihang range-frontal fault (including the Yuanshi fault, the Handan fault and the Tangxi fault)The Handan fault is a major bounding fault between The Taihangshang uplift area and North China depression area in SANCC. Near the faut, gravity anomaly belt and crustal deformation transition belt can be noticed. Low gravity anomalies and positive vertical deformation appear in its western area, while the values are just on the contrary in its eastern area. According to the survey of broad band array and small earthquakes relocation and interpretation of oil seismic profiles, The Handan fault does not control the sedimentary of the Handan depression, which is a listric nomal fault with dip 70 degrees and fault throw up to 4000~5000m and is composed of sevaral sub-faults.There maybe a basal fault extending to the detachment fault (Paleo-Taihangshan fault) under the Handan fault.(3) The Cixian-Daming faultThe Cixian-Daming fault is the bounding fault between The Linqing depression and Neihuang uplift. The fault can be divided into three segments, the Daming-Linzhang segment, the Cixian-Fengfeng segment and the Nanshancun-Chakou segment, which are characteristic of buried faults and moderate earthquakes, buried faults and surface fractures, respectively.(4) The Qumo faultThe south-dipping Qumo fault is the north boundary fault of the Handan sub-depression, with length 60km, strike 290 degrees and dip 70-80 degrees. The fault extends to the Permian and Triassic formation with dislocation 1200m. The arc-like fault merges into the East Handan fault with reducing throw. The 1708 (M5.5) earthquake occurred near the convergence area with East Handan fault.(5) The West Zishan faultThe West Zishan fault begins west of Xintai city, extends along the west of Zishan mountains, vanishing near Boyan county, with length 70km, strike NNE, west-dipping. According to the survey of broad band array and small earthquakes relocation, there is a fault extending to deep crust.(6) Fault systemThe fault system of the Handan sub-depression can be divided into three units, which are surface fault unit (0~2km), middle fault unit (0.1~9km) and lower fault unit (10~12km). The lower fault unit is mainly composed of the paleo-Taihangshan fault, and many faults of the middle faults unit merge into the lower fault unit-detachment plane.All in above, the faults trending NE developed later relatively than the faults of NWW strike. But the Taihangshan fault was cut by the Qumo fault because of the intensive activity of Qumo fault. There are three transition zones in SANCC, which are the Longyao transition zone, Qumo transition zone and Maling transition zone from north to south.2. Evolution of Meso-Cenozoic tectonicsThe Indosinian movement in the early Mesozoic occurred widespreadedly in the whole China and formed the tectonic regime of uplift in the east and depression in the west which extend in NE-NNE. The uplift in the east continued intensively with the left-lateral shearing and compressing in the Yanshan movement. With the leteral compressing and deep heating, the thickness of lithosphere and continental crust incresed sharply. Under the tectonic background, the Zanhuang metamorphic core complexes were formed, which indicated the deep heating and deep crustal faults.According to the tectonic evolution history, the sedimentary sequences in SANCC experienced marine and land facies(Permian), fluvial and lacustrine facies (Triassic, Jurassic and Cretaceous), fault depression (Paleogene), depression (Neogene) in turn. The sedimentary sequences and tectonic evolution history reflected the influence of plate movement and deep heating.3. NCC destruction and lithosphere thinningThrough studies on the sedimentary sequences, this thesis determines the mechanism of transition from thrusting to extension, regional extensional kinematics and process of extension by taking metamorphic core complexes as the window. The NCC destruction can be divided into three stages including pre-destruction stage(257~161Ma), destruction developing stage(161~65Ma) and destruction stage(65~0Ma). Based on the chacteristics of sedimentary sequences, the weak sedimentary process responsed to the deep intensive heating events in late Jurassic-Cretaceous, while intensive sedimentary process responsed to the deep weak heating events in the Paleogene.As the sedimentary process has less relationship to the heating events in the craton basin, two kinds of manners of NCC destruction can be estimated: first, mantle active uplift and crust passive extention, second, crust active extention and mantle passive uplift. This study has improved the research on the extensional tectonics of the NCC and helped to make clear the crustal response to the lithospheric thinning and deep dynamics of destruction of the NCC.4. Interpretation of gravity anomalies along the Taihangshan mountainsBased on the survey of broad band array and small earthquakes relocation, the crustal interfaces are all nearly horizontal and no deep crustal faults exist to the east of Handan fault. Combined with the neutral and alkaline magma along the west of the Zishan fault, this work can draw a conclusion that there is a deep crust fault under the mountains. So the gravity anomalies is the result of double actions of the deep crust fault and the Moho boundary depression.5. Crust structure in the Handan sub-depression and surrouding areasThe crust structure in the Handan sub-depression and its surrouding areas was given by broadband array observations. The crustal interfaces changed smoothly, and the Moho boundary is high in the north and low in the south. A low velocity anomal belt can be found under the West Zishan fault by small earthquakes relocation, concentrating in the depth range 10~20km. The crust structure can be divided into 4 structural units including the upper crust, the middle crust, the lower crust and the Moho boundary. 6. Relationshiop between earthquakes and seismgenic structure of SANCCIn SANCC, two great earthquakes have occurred since 1830, i. e. 1830 (M7 1/2)and 1966 (M7.2) earthquakes which are located in Cixian and Xintai seismotectonic province, respectively. These two provinces lie in the Tangshan-Hejian-Cixian earthquake belt and has a seismic gap between them. The Qumo weakly active fault just passes through the seismic gap.In Cixian seismotectonic province, the small earthquakes are located in a depth range 10~20km which is abundance of low velocity bodies. The crystalline basement and early Paleozoic brittle layers of NCC maybe a stress accumulating area because of the existence of low velocity bodies. Therefore it would produce grand earthquakes when the strain accumulation reaches the critical value.All in above, the mechanism of the earthquakes occurred in Craton is: the existence of deep crust fault serves as the channel of molten lava, which forms the low velocity bodies under the crystalline basement. When the accumulation of stress reaches critical point of the crystalline basement, earthquakes will occur.7.Seismogenic stucture modelThe seismogenic structure model has been obtained based on the previous studies and the data from the project of active fault surveying. In the same while, earthquake prediction has been attempted by finite element simulation. The prediction shows that the dangerous region maybe in the western hanging wall of the Qumo fault and the earthquake occurrence period maybe in the next 100 years, with magnitude probably M6.0~M7.0.更多还原