FAULT ACTIVITY OF THE SOUTHWESTERN SEGMENT OF THE EASTERN BRANCH OF XINYI-LIANJIANG FAULT ZONE IN GUANGDONG PROVINCE

The NE-trending Xinyi-Lianjiang fault zone is a tectonic belt, located in the interior of the Yunkai uplift in the west of Guangdong Province, clamping the Lianjiang synclinorium and consisting of the eastern branch and the western branch. The southwestern segment of the eastern branch of Xinyi-Lianjiang fault zone, about 34km long, extends from the north of Guanqiao, through Lianjiang, to the north of Hengshan. However, it is still unclear about whether the segment extends to Jiuzhoujiang alluvial plain or not, which is in the southwest of Hengshan. If it does, what is about its fault activity? According to ‘Catalogue of the Modern Earthquakes of China’, two moderately strong earthquakes with magnitude 6.0 and 6.5 struck the Lianjiang region in 1605 AD. So it is necessary to acquire the knowledge about the activity of the segment fault, which is probably the corresponding seismogenic structure of the two destructive earthquakes. And the study on the fault activity of the segment can boost the research on seismotectonics of moderately strong earthquakes in Southeast China. In order to obtain the understanding of the existence of the buried fault of the southwestern segment, shallow seismic exploration profiles and composite borehole sections have been conducted. The results indicate its existence. Two shallow seismic exploration profiles show that buried depth of the upper breakpoints and vertical throw of the buried fault are 60m and 4~7m(L5-1 and L5-2 segment, the Hengshan section), 85m and 5~8m(L5-3 segment), 73m and 3~5m(Tiantouzai section), respectively and all of them suggest the buried fault has offset the base of the Quaternary strata. Two composite borehole sections reveal that the depth of the upper breakpoints and vertical throws of the buried segment are about 66m and 7.5m(Hengshan section) and 75m and 5m(Tiantouzai section), respectively. The drilling geological section in Hengshan reveals that the width of the fault could be up to 27m. Chronology data of Quaternary strata in the two drilling sections, obtained by means of electron spin resonance(ESR), suggest that the latest activity age of the buried fault of the southwestern segment is from late of early Pleistocene(Tiantouzai section) to early stage of middle Pleistocene(Hengshan section). Slip rates, obtained by Hengshan section and Tiantouzai section, are 0.1mm/a and 0.013mm/a, respectively. As shown by the fault profile located in a bedrock exposed region in Shajing, there are at least two stages of fault gouge and near-horizontal striation on the fault surface, indicating that the latest activity of the southwestern segment is characterized by strike-slip movement. Chronology data suggest that the age of the gouge formed in the later stage is(348±49) ka.     

RESEARCH ON THE CHARACTERISTICS OF QUATERNARY ACTIVITIES OF SU-XI-CHANG FAULT

Running across the urban areas of Changzhou, Wuxi and Suzhou, the NW-trending Su-Xi-Chang Fault is an important buried fault in Yangtze River Delta. In the respect of structural geomorphology, hilly landform is developed along the southwest side of the Su-Xi-Chang Fault, and a series of lakes and relatively low-lying depressions are developed on its northeast side, which is an important landform and neotectonic boundary line. The fault controlled the Jurassic and Cretaceous stratigraphic sedimentary and Cenozoic volcanic activities, and also has obvious control effects on the modern geomorphology and Quaternary stratigraphic distribution. Su-Xi-Chang Fault is one of the target faults of the project "Urban active fault exploration and seismic risk assessment in Changzhou City" and "Urban active fault exploration and seismic risk assessment in Suzhou City". Hidden in the ground with thick cover layer, few researches have been done on this fault in the past. The study on the activity characteristics and the latest activity era of the Su-Xi-Chang Fault is of great significance for the prevention and reduction of earthquake disaster losses caused by the destructive earthquakes to the cities of Changzhou, Wuxi and Suzhou. Based on shallow seismic exploration and drilling joint profiling method, Quaternary activities and distribution characteristics of the Su-Xi-Chang Fault are analyzed systematically. Shallow seismic exploration results show that the south branch of the Su-Xi-Chang Fault in Suzhou area is dominated by normal faulting, dipping to the north-east, with a dip angle of about 60° and a displacement of 3~5m on the bedrock surface. The north branch of the Su-Xi-Chang Fault in Changzhou area is dominated by normal faulting, dipping to the south, with a dip angle of about 55°~70° and a displacement of 4~12m on the bedrock surface. All breakpoints of Su-Xi-Chang Fault on the seismic exploration profiles show that only the bedrock surface was dislocated, not the interior strata of the Quaternary. On the drilling joint profile in the Dongqiao site of Suzhou, the latest activity of the south branch of Su-Xi-Chang Fault is manifested as reverse faulting, with maximum displacement of 2.9m in the upper part of Lower Pleistocene, and the Middle Pleistocene has not been dislocated by the fault. The fault acts as normal fault in the Pre-Quaternary strata, with a displacement of 3.7m in the Neogene stratum. On the drilling joint profile in the Chaoyang Road site of Changzhou, the latest activity of the north branch of Su-Xi-Chang Fault is manifested as reverse faulting too, with maximum displacement of 2.8m in the bottom layer of the Middle Pleistocene. The fault acts as normal fault in the Pre-Quaternary strata, with a displacement of 10.2m in the bedrock surface. Combining the above results, we conclude that the latest activity era of Su-Xi-Chang Fault is early Middle Pleistocene. The Su-Xi-Chang Fault was dominated by the sinistral normal faulting in the pre-Quaternary period, and turned into sinistral reverse faulting after the early Pleistocene, with displacement of about 3m in the Quaternary strata. The maximum magnitude of potential earthquake on the Su-Xi-Chang Fault is estimated to be 6.0.     

滨北地区埕南断层晚更新世活动证据及其地震危险性意义

埕南断层是埕宁隆起与济阳凹陷的边界断层,也是滨北地区1条规模最大的重要断层,采用浅层地震勘探和钻孔联合剖面探测相结合的方法,确定了埕南断层准确位置,探明了断层的产状,揭露了上断点深度。钻探结果显示,埕南断层为正断特征,倾向南或南东,倾角70°～80°,断层上断点埋深44.3～46.4 m,断距1.0～1.3 m。通过年代学测试确定了错断地层的年代,获得埕南断层错断晚更新世地层的证据,埕南断层晚更新世活动证据的发现对滨北地区地震危险性再认识具有重要意义和价值。     

太原市汾河断裂浅层高分辨率地震探测

通过浅层高分辨率地震探测 ,结合钻孔资料 ,获得了测线处汾河断裂的准确位置 ,几何结构 ,活动性质、时代和速率等参数 ,并对其动力学属性进行了初步的讨论。地震探测揭露出汾河断裂的西支断层 ,为高角度东倾的斜滑断层 ,切割了第四系下部 ,上断点位于地下约 70m处。据钻孔剖面推断有 2条高角度相向而倾的斜滑断层 ,东支位于汾河东岸 ,断至全新统—上更新统 ,其底界面垂直错距约 8m。断裂北段另一个钻孔剖面表明 ,西支断层切割了全新统—上更新统 ,底界面垂直错距约6m。汾河断裂晚更新世以来的平均垂直滑动速率为 0 0 6～ 0 0 8mm/a ,大震平均重复间隔为 5 0～6 7ka     

The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

Introduction Artificial seismic sounding is a geophysical exploration technique developed in prospectingfor oil and gas and other mineral resources and consists of reflection wave and refraction waveexploration methods. With rapid development of computer techniques and sounding instruments,the reflection wave method became a high-resolution imagery technique for underground struc-tures and is widespreadly used in detection of underground caves and in engineering exploration.In previous se…     

对1976年河北唐山MS7.8地震地表破裂带展布及位移特征的新认识

1976年河北唐山MS7.8地震发生之后,诸多资料报道了唐山市南侧展布的长8～11km的地震地表破裂带.该地表破裂带由10余条NE方向、具右旋走滑特征的地表破裂呈左阶形式组成,总体走向N30°E,最大右旋位移2.3m,多数地段的垂直位移为0.5 ～0.7m.近年有学者提出,在更大范围内出现的地表破坏现象.分辨这些地表破...     

The movement age of hidden fault and analysis on width of its effect zone from shallow seismic sounding and drilling data

Field experimental seismic sounding permitted us to obtain optimal shallow seismic reflection sounding parameters. In process of data processing, we obtained a high-qualitative shallow seismic reflection sounding profile by using the techniques such as filtering, edition surgical blanking, prediction deconvolution, fitting static correlation of first arrival time, and velocity analysis. Comprehensive analysis on the information of reflection wave groups along the seismic sounding profile and the stratigraphic and neogeochronological data obtained from many drills near the sounding line reveals that the upper termination of the detected fault zone is located at depth of 75–80 m, in the Middle Pleistocene deposits dated to be about 220 ka BP. The continuity, discontinuity, increasing and decreasing amount of reflection wave groups and change of their configurations, in combination with geological columns of drills, permitted us to know that the width of upper termination of the fault zone is 100 m. It can be inferred from the variation of number of reflection wave groups along the profile that the scarp of hidden fault is 200 m wide and the fault is a synsedimentary active fault in the Early Pleistocene and the early stage of Middle Pleistocene. No tectonic movement, which offset the covering deposits, had occurred since the late stage of Middle Pleistocene. Foundation item: A High-new Technique Project by State Development and Planning Commission of China (2001977).     

浅层地震勘探资料地质解释过程中值得重视的问题

浅层地震勘探是第四系覆盖区隐伏断层活动性研究常用的手段,叠加剖面上反射波组的分叉、合并、弯曲、中断、尖灭等被用作判断断层存在的重要标志。松花江北的吕刚屯、巨宝屯浅层地震叠加剖面上,T0为下更新统砂砾石层等松散堆积和白垩系砂岩、泥岩的分界面,反射波组清晰。T0-1波组为砂砾石层和黏土层、或砂砾石层和粉细砂层的反射界面,反射波组振幅大,能量强。根据地震反射剖面和测线上的钻孔资料,认为阿什河断层错断了下更新统下段,滨州断层错断了上更新统下段。而通过建立高精度的钻探联合地质剖面、地层年代测试和地层对比,确认阿什河断层没有错断第四系,滨州断层错断了下更新统下段。最后,从第四系的岩性、厚度变化等解释了浅层地震叠加剖面上反射波组的中断、弯曲并非断层活动的结果,而是由第四纪地层相变引起的     

用地震反射法对玉溪盆地普渡河断裂的探测

通过在玉溪盆地用地震反射法探测普渡河隐伏断裂的实例, 阐述了在覆盖层很厚、 人口密集、 环境干扰强条件下的地震勘探方法技术. 本次勘探针对场地条件使用了大型可控震源和小检波距、 长排列、 高覆盖次数的观测系统. 获得的高信噪比时间剖面清晰地揭示了玉溪盆地内普渡河断裂的产状和规模. 勘探结果表明, 玉溪盆地覆盖层(N+Q)最大厚度超过820 m; 基岩面西陡东缓, 呈北北东走向的箕状分布; 普渡河断裂分两支穿过玉溪盆地西部, 主断裂为正断性质, 走向约N20°E, 倾向东, 视倾角75°—80°; 断裂规模由南向北逐渐变大, 基岩断距在盆地南部的大营街附近为40 m, 而在盆地北部的九龙池东部, 基岩断距增加到280 m左右, 穿过玉溪盆地西部的普渡河断裂错断了新近系上新统中上部地层.      

龙门山山前彭州隐伏断裂高分辨率地震反射剖面

彭州断裂是龙门山山前一条重要的隐伏断裂.为了调查彭州断裂的位置、性质及其活动性,5·12汶川M_S8.0地震发生后,作者采用可控震源和高精度的地震反射勘探方法,对彭州隐伏断裂进行了高分辨率地震反射成像.本文利用获得的浅层地震剖面资料并结合石油地震反射剖面,给出了彭州断裂的空间展布特征以及断裂两侧的新生代地层厚度.结果表明,彭州断裂为一条走向NE、倾向NW、倾角约为58°～62°的逆断层,该断层向上错断了第四纪沉积层,具有明显的第四纪活动,向下大约在深度8～10 km左右收敛到向西缓倾的滑脱面之上.研究结果为评价断裂的活动性和灾后重建提供了地震学证据.     

THE CENOZOIC TECTONICS AND SEISMIC ACTIVITY OF XINZHENG-TAIKANG FAULT IN THE SOUTHERN EDGE OF TAIKANG AREA

On the basis of dividing and comparison of the Neogene strata and their bottoms revealed by 7 drill holes in Taikang area, we completed 101 seismic profiles with a total length of 4991km. Seismic data were compared and interpreted. The results indicate that Xinzheng-Taikang Fault, as a blind fault extending from Xinzheng to Taikang, which was considered as an EW striking fault from Xuchang to Taikang before, is the boundary of Taikang uplift and Zhoukou depression, controlling the sedimentation since Neogene Period. So we named the fault the Xinzheng-Taikang Fault, which is composed of two branches, mainly, the east and west branches. The west branch strikes northwest, dipping northeast with steep angles, and the fault plane extending more than 140km in length. As revealed on the seismic profiles, the eastern segment of the west branch is normal fault, while the west segment of the branch shows characteristics of strike-slip fault. The east branch trends NW-NEE, dipping SW-SSE with the length of about 50km. Two branches form a minus flower structure, indicating the strike slip-extension tectonic background. The bottom of Neogene strata is offset about 120m by the east branch, 20m by the west branch, and the bottom of Quaternary is probably offset too. Meanwhile, latest studies suggest that the composite strip of the two branches of Xinzheng-Taikang Fault, which is a tectonic transfer zone, is the subduction zone between the two strike-slip faults. The tectonic stress tends to be released by the east-west branch fault, and the zone should be the seismogenic structure for the recent seismicity in Taikang area. In 2010, the latest earthquake ofM_S4.7 occurred in this area, causing 12 people wounded. The seismogenic structure was considered to be the Xinzheng-Taikang Fault. So locating the fault exactly is of great importance to disaster prevention.     

鄂尔多斯北缘断裂托克托段晚第四纪活动特征

鄂尔多斯北缘断裂作为河套断陷带和鄂尔多斯地块的边界断裂,研究其晚第四纪活动特征,对于科学评价黄河流域内蒙古河套段的地震危险性具有重要意义。本文利用野外地质调查、微地貌测量、浅层人工地震勘探及钻孔联合剖面探测相结合的方法,综合地层年代样品测试结果,确定了该断裂托克托段的准确位置和最新活动特征。研究结果表明,鄂尔多斯北缘断裂托克托段沿线构造地貌不发育,推测断裂的最新活动可能尚未达到地表,地表的地貌陡坎应为河流侵蚀成因。断裂在深、浅地震反射剖面上表现为“Ｙ”字形的张性断裂系,主断裂倾向北,分支断裂倾向南,整体上陡下缓,具有多个地堑式分布的特点。跨断裂钻孔联合剖面上显示,单个分支断裂的同震垂直位移量为2～2.5 m,最新活动时代为43.5～70 ka。鄂尔多斯北缘断裂是一条晚更新世活动的深大断裂,具有一定的地震危险性。     

昌平-丰南断裂构造浅层地震勘探新证据

昌平-丰南断裂是根据卫星遥感图像解译发现的一条隐伏活动断层,是NWW向张家口-蓬莱断裂带中规模最大的断裂,为进一步调查确认断裂的存在、空间位置、性质和断裂构造特征,并重新厘定其活动性,在卫星遥感影像解译断裂大体空间位置的基础上,布设了2条浅层地震勘探测线,对昌平-丰南断裂进行了高分辨率地震勘探,获得了测线控制范围内地下结构和断裂构造的清晰成像。结果表明,昌平-丰南断是一条倾向S、走向NWW的走滑正断层,浅层地震剖面揭示断层上断点埋深80~100 m,断错了上更新统底界,结合测线附近钻孔资料推测其最新活动时代为晚更新世。     

北京南部地壳精细结构深地震反射探测研究

为了研究北京平原区的地壳结构特征、断裂的空间展布、断裂活动性以及深浅构造关系,在北京平原区的南部完成了1条长90 km的深地震反射剖面.探测结果表明,该区地壳以双程反射时间(TWT)6～7 s的强反射带Tc为界分为上地壳和下地壳,上地壳厚约18～19 km,下地壳厚约16～17 km,Moho界面深度约为34～35 km.该区结晶基底起伏变化较大,上、下地壳分界面和Moho界面都是一个具有一定厚度的过渡带.上地壳反射层位丰富,断裂构造发育,构造形态清晰.在夏垫断裂西北,剖面揭示了4～5组能量较强的反射震相,表现为典型的隆起区特征;在夏垫断裂东南,上部为一套向东南倾伏的密集强反射层,下部为一套形态各异、结构复杂的强反射层,这些反射具有典型的沉积盆地特征,盆地最深处约为11 km.剖面揭示的地壳深断裂倾角较陡,向上切穿了上、下地壳分界面,延伸到上地壳沉积盆地的底部,向下切穿了壳幔过渡带,与上部断裂和沉积盆地构成了独特的组合关系.     

龙门山推覆构造带中段山前断裂晚第四纪活动的地质与地球物理证据

龙门山逆冲推覆构造带中段山前断裂的存在和最新活动时代一直是个争论的问题.石油地震探测资料和浅层地震剖面揭示该断裂的存在,并断错了第四系;野外调查表明,龙门山中段山前存在明显的线性地貌特征,山前断裂断错晚了更新世晚期的洪积台地;探槽剖面揭示距今约1500 a之前在山前断裂上曾发生过一次地表破裂型事件,而该断裂未来具备发生强震的潜势.断错地貌的差分GPS测量和年代学分析显示山前断裂晚第四纪垂直滑动速率大于0.36 mm/a,其与龙门山中段主干断裂活动强度相当,说明龙门山山前断裂在龙门山逆冲推覆构造带的变形中也承担着重要的作用.该研究不仅能为成都平原的地震危险性评价提供基础资料,也有助于全面理解青藏高原东缘的隆升机制.     

洱源-江川宽角地震剖面的地壳反射特征

通过对洱源-江川宽角反射地震资料的叠前偏移处理成像,得到了一个类似于近垂直入射多道地震数据的记录剖面.反射剖面图像与地壳速度结构共同揭示出地壳厚度由剖面西北端(约45 km)向东南端(约40 km)减薄.在洱源-楚雄西北附近深度约10 km处存在一组向东南倾斜的强反射震相,其东南约50 km处存在向西北倾斜的强射震相.易门断裂两侧地壳反射属性具有明显的差异,易门断裂之西北方向深度25～40 km处,中下地壳内存在两组强振幅,向东南方向上倾的地震反射同相轴,并被楚雄-建水断裂后期所错断,易门断裂之东南方向上,地壳内反射较为均一,未见特别明显的强间断面反射信息,这个反射结构被解释为印度板块东向俯冲与藏东缘地壳物质东向逃逸综合作用导致下地壳增厚和厚地壳变形的结果.     

开封断裂第四纪活动特征

开封断裂是郑州-开封断裂带的重要组成部分,也是黄河中下游平原的一条重要控制性断裂。利用浅层地震勘探发现,开封断裂为总体走向EW,倾向N的正断层;断裂分为东、西2支,断裂活动性具有明显的分段特征,东支活动性较西支强。钻孔联合剖面揭示开封断裂东支断裂上断点埋深27～35 m,根据地层年代学结果,其最新活动时间为晚更新世。研究成果为开封市城乡规划、重大工程选址和地震区划工作提供了重要的基础数据。     

桥头集-东关断裂合肥盆地段活动特征

北西走向的桥头集-东关断裂与郯庐断裂带南段相交切，横跨合肥盆地及其东缘的隆起区，在合肥盆地内呈隐伏状态。本研究跨桥头集-东关断裂合肥盆地段布设3条浅层地震勘探测线，揭示断裂浅部构造特征。解译出的F_P1、F_P2和F_P3断层性质相同，倾向一致，上断点深度相近，反映出桥头集-东关断裂合肥盆地段是一条走向NW、倾向SW、具有逆断分量的断裂。3条浅层地震反射剖面中第四系的底界面反射波组T_Q呈连续近水平展布，表明桥头集-东关断裂两侧的第四系厚度无明显变化。在浅震剖面解译的基础上，布设了1条跨断层钻孔联合剖面，剖面揭露出的第四系没有被错动。结合本区第四系地层发育情况及钻孔地层年龄分析，认为桥头集-东关断裂中更新世以来不活动。根据本文探测结果，尚不能排除桥头集-东关断裂早更新世有一定的弱活动。     

从地震折射和反射剖面结果讨论唐山地震成因

通过唐山震中的地震测深以及深反射剖面,揭示了唐山震源区的浅部及深部构造图象,它与以往的推测很不相同。 唐山东面的开平向斜属中生代构造,探测的结果表明,向斜轴是一近于直立的地壳断裂。唐山地震时的水平地形变主要是由开平地壳断裂的位移引起的,它是北北东-南南西向右旋走滑断裂。开平地壳断裂西面的陡河断层是一自地表向南东方向下插的正断层,断层倾角为26°,延伸至5km深处。陡河正断层刚好插到唐山市震中区的正下方。唐山地震时的垂直地形变主要是由陡河正断层的滑动引起的。 野鸡坨-丰台断层通过震源区的西部边缘,断层以西的第四纪沉积层,在过去一百万年间曾经沿北北东方向水平滑移15km,表明它也是一个右旋的走滑断层。但是它在近代数百年间并无地震活动,唐山地震时该断层的滑动亦不明显。 开平地壳断裂和陡河正断层在唐山地震时同时滑动,说明地震的作用力除区域水平构造力外,地壳上方还存在一个附加的引张力。在开平断裂处,上部地壳的反射面倾角杂乱,而且在它的正下方,莫霍界面明显错断,因此,地幔顶部的热物质可能自开平地壳断裂中上升。热物质产生的热应力在地壳上方可表现为张应力,而在地壳下方却表现为压应力,这与反射地震剖面图的现象相符合。开平地壳断裂中热物质的上升对地震的产生有     

Processing and preliminary interpretation of noisy high-resolution seismic reflection/refraction data across the active Ostler Fault zone,South Island,New Zealand

In an attempt to understand the structure of active faults as they emerge from bedrock into shallow semi-consolidated and unconsolidated sediments, we have recorded a comprehensive high-resolution seismic reflection/refraction data set across the Ostler Fault zone on the central South Island of New Zealand. This fault zone, which absorbs 1–2 mm/yr of compression associated with oblique convergence of the Pacific and Australian tectonic plates, consists of a series of surface-rupturing N–S trending, west-dipping reverse faults that offset a thick sequence of Quaternary glacial outwash and late Neogene fluvio-lacustrine sediments of the Mackenzie Basin. Our study focuses on a region of the basin where two non-overlapping fault segments are separated by a transfer zone. Deformation in this area is accommodated by offsets on multiple small faults and by folding in their hanging walls. The seismic data with source and receiver spacing of 6 and 3 m and nominal CMP fold of 60 was acquired along twelve 1.2 km long lines orthogonal to fault strike and an additional 1.6 km long tie-line parallel to fault strike. The combination of active deformation and shallow glacial outwash sediments results in particularly complicated seismic data, such that application of relatively standard processing schemes yields only poor quality images. We have designed a pre- and post-stack reflection/refraction processing scheme that focuses on minimising random and source-generated noise, determining appropriate static corrections and resolving contrasting reflection dips. Application of this processing scheme to the Ostler Fault data provides critical information on fault geometry and offset and on sedimentary structures from the surface to ～ 800 m depth. Our preliminary interpretation of one of the lines includes complex deformation structures with folding and multiple subsidiary fault splays on either side of a ～ 50° west-dipping primary fault plane.