磁县断裂带的构造和地震活动特征

磁县断裂带是华北地震区中重要的断裂之一,1830年该断裂带发生了M7级地震.从分析该带的构造特征和地震活动特征出发,在结合历史地震活动和现今地震活动基础上,利用震级-时间模型对磁县断裂带未来强震活动进行预测,结果表明,未来该段中南的总体活动水平维持在5级左右.     

河北磁县北西西向南山村－岔口活动断裂带活动特征与1830年磁县地震

河北磁县西部北西西向南山村－岔口活动断裂为北西西向磁县活动断裂西段，全长３５ｋｍ，又可再分为东西两段。全新世时期该断裂有多次活动，活动方式以具左旋性质的正倾滑为主。１８３０年磁县７．５级地震时，南山村－岔口断裂带出现新的地表破裂，地表垂直位移多处为２～４ｍ，最大约７ｍ。据目前资料，该断裂带最新两次地震事件的时间间隔约为３５００ａ。最近获取的位于磁县最高峰老爷山庙宇碑文资料，补充说明了邻近岔口活动断裂带的古建筑物在１８３０年地震中的严重破坏。     

河北磁县北西西向南山村－岔口活动断裂带活动特征与1830年磁县地震

河北磁县西部北西西向南山村－岔口活动断裂为北西西向磁县活动断裂西段，全长３５ｋｍ，又可再分为东西两段。全新世时期该断裂有多次活动，活动方式以具左旋性质的正倾滑为主。１８３０年磁县７．５级地震时，南山村－岔口断裂带出现新的地表破裂，地表垂直位移多处为２～４ｍ，最大约７ｍ。据目前资料，该断裂带最新两次地震事件的时间间隔约为３５００ａ。最近获取的位于磁县最高峰老爷山庙宇碑文资料，补充说明了邻近岔口活动断裂带的古建筑物在１８３０年地震中的严重破坏     

1830年河北磁县7.5级地震的若干问题

本文讨论了与1830年磁县7.5级地震有关的下列问题:1、区域构造环境,指出太行山山前断裂带南部被隐伏的北西西向构造带阻隔,形成应力集中区,构成磁县7.5级地震的区域构造条件;2、根据地质构造、震源机制、地壳应力测量资料,讨论了华北平原地区的北东东(近东西)向挤压应力场;3、介绍了朝城—大名—磁县—涉县隐伏断裂的地质构造和地震活动特征;4、磁县7.5级地震的前震活动,发震一年之前5个5级地震形成包围圈;5、磁县7.5级地震的极震区等震线为北西西向,与同向隐伏断裂的展布相吻合.     

大凉山次级块体内强震发生的构造特征与2014年鲁甸6.5级地震对周边断层的影响

2014年8月3日,在云南鲁甸发生MS6.5地震.该地震位于巴颜喀拉块体、川滇块体与华南块体三者之间的以挤压和左旋走滑为主要活动特征的大凉山次级块体内部.该次级块体吸收了来自川滇块体和巴颜喀拉块体的挤压作用,主要以各边界断裂带的挤压作用和内部大凉山断裂带、峨边断裂带等NNW向的左旋走滑次级断裂为主要特征;在历史上大凉山次级块体边界上以7级以上强震活动为主要特征,而在次级块体内部则以5级地震频繁活动为主.2014年鲁甸MS6.5地震发生在逆冲走滑断裂带内部的NNW向左旋走滑断裂上,该地震主要受到了发生在小江断裂带上的1733年M73/4和则木河断裂带上的1850年M71/2强震的影响,这两次地震对2014年鲁甸MS6.5地震有促进作用,而2014年鲁甸6.5级地震促进了2014年10月1日越西5.0级地震的发生,此外鲁甸地震对大凉山断裂带北段、峨边断裂带、昭通-鲁甸断裂带东段以及则木河断裂带南段有一定的库仑应力增强作用.     

磁县-大名断裂东段第四纪活动性

依据浅层地震勘探结果、钻孔和重力资料,进一步厘定了磁县-大名断裂东段的空间展布、断层上断点埋深.研究认为该断裂具有分段活动特征,最新活动时代为中—晚更新世,并推测出磁县-大名断裂东延至范县古城镇南一带.     

晋冀豫交界一维速度模型研究

<正>晋冀豫交界地区分布着磁县断裂带、安阳断裂带以及林县断裂带等。磁县断裂带是华北地震区一个次级构造单元,以太行山山前断裂带的邯郸断裂为界,其西为新生代的太行山隆起区,以东为华北平原凹陷区,该断裂走向为NWW,是中生代以来长期发育的一条断裂[10]。林县地区处于太行山隆起区的南部,断裂带走向为NNE,为林县历史时期与近期地震活动的一个重要地质背景。这些断裂带的地质构造较为复杂,在历史上曾多次发生过强震或者中强震,如1830年磁县发生7.5级强震,具有中强地震的发生背景。精确     

嫩江断裂带北段的第四纪活动特征初步研究

嫩江断裂带是松辽盆地的西边界断裂，但受第四系强覆盖等研究条件的限制，前人对该断裂第四纪构造活动的研究较少。本文针对该断裂带北段开展了野外地质调查，并综合大地电磁测深和纵波速度结构等结果，初步研究了嫩江断裂带北段的第四纪活动特征。调查发现，该断裂北段主要发育地貌陡坎、基岩滑坡、地层揉皱变形、近垂直擦痕、基岩崩塌与线性断塞塘等特征。探槽古地震研究揭示断裂带北段在（80.9±4.6）—（62.9±2.3）ka BP曾发生1次古地震事件，运动方式为正断，垂直位移量约1.5m，震级约为M_S 7.1—7.3，断裂在晚更新世曾发生过强烈活动。研究结果有助于认识了解该断裂和松辽盆地的第四纪构造变形过程，并为评价该断裂及邻区的地震活动潜势提供参考。     

小江断裂带及周边地区强震危险性分析

根据历史地震资料及现今区域台网中小地震观测资料,对小江断裂带及周边地区的历史地震活动特征,特别是小江断裂带不同段落的现今断层活动习性进行了研究,依据b值,结合其它地震活动性参数,勾画出了该区未来强震的潜在危险区:①石屏一建水断裂段6.8级地震重现期为88～193年,目前已平静121年;小江断裂带的宜良-嵩明段6.8级地震蕈现期是108～225年,目前已平静175年.②小江断裂东川段具有中等偏大应力水平,属于中小地震活动频繁的地段;小江断裂华宁段具有较低应力水平,属于以小震活动为主的地段;通海-峨山断裂具有中等应力水平,属于中小地震活动频繁地段.③石屏-建水断裂和小江断裂宜良-嵩明段存在较低的6值和较小强震复发周期,具有较高应力水平,属于潜在地震震级偏大的区域,是未来发生7级以上大震的潜在危险区.     

龙门山断裂带中上地壳速度结构的短周期环境噪声成像

本文利用在龙门山断裂带周边布设的57个台站自2008年11月至2009年11月为期一年的垂直分量连续地震环境噪声数据,通过短周期地震环境噪声成像方法,获得了龙门山断裂带中北段地壳25km深度范围的S波精细速度结构.结果表明:(1)龙门山断裂带周边区域10km以上的速度结构与地表断裂的分布形态具有良好的一致性,速度结构控制了龙门山主要断层的深部延展特征;在15km及以下深度,S波速度结构呈现沿龙门山和沿岷山隆起走向的交叉构造格局,由此造成的速度结构差异可能影响了汶川地震的破裂过程;(2)速度结构随深度的分布特征为龙门山断裂带主要断层的深部延伸形态给出了良好的约束,结果进一步确认了龙门山断裂中段的高角度铲型断裂构造特征;(3)研究区的南端发现了龙门山断裂下方20km以下深度具有与松潘地块中地壳低速层相关的低速结构的迹象,这可能是汶川地震破裂带南段22km左右深度存在脆韧转换带的一个证据.研究结果显示出密集台阵和短周期环境噪声成像方法在地壳浅部精细结构和断层探测研究中具有巨大潜力.     

用现今小地震研究历史强震的震源断层——以1830年河北磁县7(1/2)级地震为例

１８３０年磁县７１２级地震是一个活动水平高、持续时间长的强震序列。近年来邯郸遥测地震台网记录到沿磁县地震极震区方向发生的大量小地震。根据对这些小地震的震源位置、震源机制的三维空间分布的分析,认为磁县地震的震源断层是ＮＷＷ向近于直立的左旋走滑断层,它和磁县地震的等震线、地表破裂带特征相符合。这个例子说明在地震学和地震地质学相结合的基础上,有可能由历史大地震区内现今小地震的群体特征,推测历史大地震的震源断层空间取向及其运动方式     

镇江地区主要NW向断裂的第四纪活动性

五峰山-西来桥断裂和丹徒-建山断裂是镇江地区2条主要的NW向断裂,可能与镇江多次破坏性地震相关。文中通过浅层地震勘探和钻孔联合剖面探测方法,对五峰山-西来桥断裂和丹徒-建山断裂的展布特征及第四纪活动性进行了系统研究。五峰山-西来桥断裂在浅层地震剖面上倾向NE,倾角约为60°,断距约为5~9m,以正断活动为主;大路镇场地上,该断裂断错的最新地层为中更新统底部,位错量为2m,判断五峰山-西来桥断裂的最新活动时代为中更新世早期。丹徒-建山断裂在浅层地震剖面上倾向SW,倾角约为50°~55°,断距约为2~7m,以正断活动为主;访仙镇场地上,中更新统之上的地层没有被断错的迹象,中更新统底部可能被断层影响,判断丹徒-建山断裂的最新活动时代为早更新世—中更新世早期。     

宁夏吴忠地区北部的浅部结构和隐伏断裂——地震反射剖面结果

应用浅层地震勘探法对宁夏吴忠地区北部的浅部地壳结构和隐伏活动断裂进行研究。结果表明,该区存在2条隐伏断裂,分别为银川主断层南段和新华桥断层。推测银川主断层南段为近SN走向的W倾正断层,断层下盘地层界面一般呈近水平状展布,而在断层上盘,T_Q及其以下的地层界面向断面方向倾伏并显示出逆牵引现象,断层向上错断了第四系内部。钻孔联合地质剖面及浅层地震探测结果共同揭示新华桥断层为一条走向NE,倾向SW的正断层,深、浅地震测线控制的新华桥断层延伸长度9 km左右,向上错断了第四系内部的T_(02)界面。     

龙门山南段前缘地区活褶皱-逆断层运动学机制——以芦山地震为例

2013年4月20日发生在龙门山南段的芦山MS7.0地震是继发生在龙门山中北段的汶川MS8.0地震之后的又一次强震。本文通过震后地表变形特征、余震分布、震源机制解、石油地震勘探剖面、历史地震数据等资料,结合前人对龙门山南段主干断裂、褶皱构造特征的研究以及野外实地考察,应用活动褶皱及"褶皱地震"的相关理论,初步分析芦山地震的发震构造模式。认为芦山地震为典型的褶皱地震,发震断裂为前山或山前带一隐伏断裂。构造挤压产生的地壳缩短大部分被褶皱构造吸收。认为龙门山南段前缘地区具有活褶皱-逆断层的运动学特征,表明龙门山逆冲作用正向四川盆地内部扩展。     

NEW EVIDENCE ON NE-SEGMENT OF JINTAN-RUGAO FAULT DISCOVERED BY SHALLOW SEISMIC EXPLORATION METHOD

The NE-trending regional deep fault, i.e. the Jintan-Rugao Fault, is a boundary fault between the Subei depression and Nantong uplift, and its research has always received broad attention because of its importance and complexity. For the absence of definite proof, there is little consensus regarding the structure and spatial distribution of the fault among geoscientists, and its latest active time is ambiguous. The study of Quaternary activity characteristics of the Jintan-Rugao Fault is of great significance for earthquake trend prediction and engineering safety evaluation, and for earthquake prevention and disaster reduction in Jiangsu Province. In order to investigate the spatial location, characteristics and tectonic features and redefine the activity of the NE-segment of the Jintan-Rugao Fault, and on the basis of likely location and marker beds derived from petroleum seismic exploration sections, we collect and arrange 4 shallow seismic exploration profiles crossing the fault to conduct high-resolution seismic reflection imaging, following the working concept of ‘from known to unknown, from deep to shallow’. In this study, an observation system with trace intervals of 4~6m, shot intervals of 12~18m, and channels of 90~256 and 15~36 folds is used. In addition, by introducing different tonnage vibroseis to suppress the background noise, the raw data with high SNR(signal-noise ratio)can be obtained. By using the above working method and spread geometry, we obtained clear imaging results of the subsurface structure and fault structure in the coverage area of the survey lines. This exploration research accurately locates the NE-segment of Jintan-Rugao Fault, and further shows that it is not a single fault but a fault zone consisting of two normal faults with N-dipping and NE-striking within the effective detection depth. The shallow seismic profiles reveal that the up-breakpoint on the south branch with stronger activity is at depth of 235~243m, which offsets the lower strata of lower Pleistocene. Combining drilling data around the survey lines, we infer the activity time of this fault is early Pleistocene. The results of this paper provide reliable seismological data for determining the location and activity evaluation of the NE-segment of Jintan-Rugao Fault. In eastern China, where the sedimentary layer is thicker, the latest active age of faults can not be determined entirely according to the latest faulted strata. For a fault passing through the thicker area of new deposits, its latest active age should be based on the tectonic background, seismic activity, present tectonic stress field, topographic deformation, structural micro-geomorphological characteristics, sedimentary thickness of new strata, controlling effect of faults on new strata and the latest strata of faults, and combined with upper breakpoints, morphology, structure and occurrence of faults, the active state of the target concealed faults should be analyzed. If the activity of the fault is judged only by the upper faulted point, it may lead to overestimating the age of the fault activity.     

NUMERICAL SIMULATION OF DEFORMATION MOVEMENT AND STRESS ACCUMULATION IN LONGMENSHAN AND ITS ADJACENT FAULTS BEFORE WENCHUAN EARTHQUAKE

In order to reveal the deformation and cumulative stress state in Longmenshan and its adjacent faults before Wenchuan earthquake,a 3D viscoelastic finite element model,which includes Longmenshan,Longriba,Minjiang and Huya faults is built in this paper.Using the GPS measurement results of 1999-2004 as the boundary constraints,the deformation and movement of Longmenshan fault zone and its adjacent zones before Wenchuan earthquake are simulated.The conclusions are drawn in this paper as follows:First,velocity component parallel to Longmenshan Fault is mainly absorbed by Longriba Fault and velocity component perpendicular to the Longmenshan Fault is mainly absorbed by itself.Because of the barrier effect of Minjiang and Huya faults on the north section of Longmenshan Fault,the compression rate in the northern part of Longmenshan Fault is lower than that in the southern part.Second,extending from SW to NE direction along Longmenshan Fault,the angle between the main compressive stress and the direction of the fault changes gradually from the nearly vertical to 45 degrees. Compressive stress and shear stress accumulation rate is high in southwest segment of Longmenshan Fault and compressive stress is greater;the stress accumulation rate is low and the compressive stress is close to shear stress in the northeast segment of the fault.This is coincident with the fact that small and medium-sized earthquakes occurred frequently and seismic activity is strong in the southwest of the fault,and that there are only occasional small earthquakes and the seismic activity is weak in the northeast of the fault.It is also coincident with the rupture type of thrust and right-lateral strike-slip of the Wenchuan earthquake and thrust of the Lushan earthquake.Third,assuming that the same type and magnitude of earthquake requires the same amount of stress accumulation,the rupture of Minjiang Fault,the southern segment of Longmenshan Fault and the Huya Fault are mainly of thrust movement and the earthquake recurrence period of the three faults increases gradually.In the northern segment of Longriba Fault and Longmenshan Fault,earthquake rupture is of thrusting and right-lateral strike-slip. The earthquake recurrence period of former is shorter than the latter.In the southern segment of Longriba Fault,earthquake rupture is purely of right-lateral strike-slip,it is possible that the earthquake recurrence period on the fault is the shortest in the study region.     

Stress changes on major faults caused by <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript>7.9 Wenchuan earthquake,May 12, 2008

On May 12, 2008, a magnitude 7.9 earthquake ruptured the Longmenshan fault system in Sichuan Province, China, collapsing buildings and killing tens of thousands people. As predicted, aftershocks may last for at least one year, and moreover, large aftershocks are likely to occur. Therefore, it is critical to outline the areas with potential aftershocks before reconstruction and re-settling people as to avoid future disasters. It is demonstrated that the redistribution of stress induced by an earthquake should trigger successive seismic activity. Based on static stress triggering theory, we calculated the coseismic stress changes on major faults induced by the Wenchuan earthquake, with elastic dislocation theory and the multilayered crustal model. We also discuss the stress distribution and its significance for future seismic activity under the impact of the Wenchuan earthquake. It is shown that coulomb failure stress (CFS) increases obviously on the Daofu-Kangding segment of the Xianshuihe Fault, the Maqu and Nanping segment of the Eastern Kunlun Fault, the Qingchuan Fault, southern segment of the Minjiang Fault, Pengxian-Guanxian Fault, Jiangyou-Guangyuan Fault, and Jiangyou-Guanxian Fault. The increased stress raises the probability of earthquake occurrence on these faults. Since these areas are highly populated, earthquake monitoring and early disaster alarm system are needed. CFS increases with a magnitude of 0.03–0.06 MPa on the Qingchuan Fault, which is close to the northern end of the rapture of Wenchuan earthquake. The occurrence of some strong aftershocks, including three events with magnitude higher than 5.0, indicates that the seismic activities have been triggered by the main shock. Aftershocks seem to migrate northwards. Since the CFS change on the Lueyang-Mianxian Fault located on the NEE of the Qingchuan Fault is rather small (±0.01 MPa), the migration of aftershocks might be terminated in the area near Hanzhong City. The CFS change on the western Qinling Fault is around 10 Pa, and the impact of static triggering can be neglected. The increment of CFS on the Pengxian-Guanxian Fault and Beichuan-Yingxiu Fault southwest to the main rupture is 0.005–0.015 MPa, which would facilitate earthquake triggering in these areas. Very few aftershocks in these areas indicate that the accumulated stress has not been released sufficiently. High seismic risk is predicated in these areas due to co-seismic CFS loading. The Wenchuan earthquake released the accumulated CFS on the Fubianhe Fault, the Huya Fault, the Ha’nan-Qingshanwan Fault, and the Diebu-Bailongjiang Fault. The decrement of CFS changes on the Longquanshan Fault east to Chengdu City is about 0.002 MPa. The seismic activity will be depressed by decrement of CFS on these faults. Supported by Knowledge Innovation Program of Chinese Academy of Sciences (Grant No. KZCX-SW-153), National Natural Science Foundation of China (Grant Nos. 40574011 and 40474028)     

九寨沟M_S7.0地震对巴颜喀拉块体东北缘活动断裂影响的有限元模拟

在详细调研地震地质资料的基础上,构建了巴颜喀拉地块东北缘三维有限元模型。以九寨沟M_S7.0地震同震位错为荷载,模拟计算了九寨沟地震的发生对巴颜喀拉块体东北缘主要活动断裂加卸载效应的影响。模拟结果显示,九寨沟地震的发生对龙日坝断裂、虎牙断裂、青川-平武断裂西段、迭部-白龙江断裂西段和东段、临潭-宕昌断裂东段,以及处于甘青川交界危险区内的东昆仑断裂东段、塔藏断裂西段,处于六盘山南-西秦岭东危险区的西秦岭北缘断裂东段表现为库仑应力加载;对岷江断裂、塔藏断裂东段库仑应力卸载效应显著。     

Resistivity mapping using the VLF-MT method around surface fault ruptures of the 1995 Hyogo-ken Nanbu earthquake, Japan

Abstract Distinctive fault ruptures, the Nojima Fault and Ogura Fault, appeared along the northwestern coast of Awaji Island at the time of the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). In order to delineate the shallow resistivity structures around the faults just after they formed, Very Low Frequency Magnetotelluric (VLF-MT) surveys were made at five sites along the Nojima Fault and at one site along the Ogura Fault. Fourteen transects were made at the one site on the Ogura Fault, and another transect covers the area between the two faults. Changes in apparent resistivity or phase, or both, commonly occur when crossing the surface location of one of the faults, except for the northern transects at OGR-0 on the Ogura Fault. Apparent resistivity values of less than 100 Ωm were observed for Tertiary and Quaternary sediments and values larger than 200 Ωm for granitic rocks. The resistivity structures are related to the morphological characteristics of the fault ruptures. Remarkably conductive zones (less than 10 Ωm in apparent resistivity and 30–40 m in width) were found where the surface displacement is distinct and prominent along a single fault plane. If remarkably conductive zones were formed at the time of the 1995 Hyogo-ken Nanbu earthquake, the results provide a good constraint on the dimensions of a conductive zone near the surface that was made by one earthquake. Alternatively, if characteristic resistivity structures existed prior to the earthquake, the conductive zone was probably formed by some tens of earthquakes in relatively modern times. In this case, this phenomenon is inferred to be a concentration of fracturing in a narrow zone and is associated with the formation of clay minerals, which enhance rock conductivity.     

NEW EVIDENCES OF HOLOCENE ACTIVITY IN THE JIANGSU SEGMENT OF ANQIU-JUXIAN FAULT OF THE TANLU FAULT ZONE

Anqiu-Juxian Fault is an important fault in the Tanlu fault zone, with the largest seismic risk, the most recent activity date and the most obvious surface traces. It is also the seismogenic fault of the Tancheng M8 1/2 earthquake in 1668. There are many different views about the southern termination location of surface rupture of the Tancheng earthquake and the Holocene activity in Jiangsu segment of this fault. Research on the latest activity time of the Jiangsu segment of Anqiu-Juxian Fault, particularly the termination location of surface rupture of the Tancheng earthquake, is of great significance to the assessment of its earthquake potential and seismic risk. Based on trench excavation on the Jiangsu segment of Anqiu-Juxian Fault, we discuss the time and characteristics of its latest activity. Multiple geological sections from southern Maling Mountain to Chonggang Mountain indicate that there was an ancient seismic event occurring in Holocene on the Jiangsu segment of Anqiu-Juxian Fault. We suggest the time of the latest seismic event is about(4.853±0.012)~(2.92±0.3)ka BP by dating results. The latest activity is characterized by thrust strike-slip faulting, with the maximum displacement of 1m. Combined with the fault rupture characteristics of each section, it is inferred that only one large-scale paleo-earthquake event occurred on the Jiangsu segment of Anqiu-Juxian Fault since the Holocene. The upper parts of the fault are covered by horizontal sand layers, not only on the trench in the west of Chonggang mountain but also on the trench in Hehuan Road in Suqian city, which indicates that the main part of the Jiangsu segment of Anqiu-Juxian Fault was probably not the surface rupture zone of the 1668 Tancheng M8 1/2 earthquake. In short, the Jiangsu segment of Anqiu-Juxian Fault has experienced many paleo-earthquake events since the late Pleistocene, with obvious activity during the Holocene. The seismic activities of the Jiangsu segment of Anqiu-Juxian Fault have the characteristics of large magnitude and low frequency. The Jiangsu segment of Anqiu-Juxian Fault has the deep tectonic and seismic-geological backgrounds of big earthquakes generation and should be highly valued by scientists.