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汶川8级大震的震中位于映秀镇,地震在映秀地区造成了多处地表破裂,如公路拱曲、地震陡坎,坡中槽新变形等,长度达300余米.经实地全站仪和GPS测量,定量分析了地表破裂的垂直分量与水平分量以及两者之间的比值,以此揭示了映秀-北川断裂的运动性质为逆冲兼右行走滑,在映秀地区逆冲分量大于走滑分量.将本次地震造成的位错数据与震前资料对比,发现汶川地震产生的地表破裂位置与地质历史上映秀-北川断裂造成的断层位错位置是相当吻合的,说明映秀地区Ⅳ级阶地上40余米的的断层陡坎可能是地质历史时期若干次大地震的结果. 相似文献
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遥感影像数据在2008年汶川地震抗震救灾和灾后恢复重建中发挥了重要的作用,充分利用遥感技术进行同震地表变形的快速识别与地震地质研究具有重要的现实意义。通过分析震后光学遥感影像的阴影、纹理等特征,以及野外获得的地表破裂变形的地质与地貌特征,总结了汶川地震同震地表变形的光学遥感影像识别特点。从遥感成像的光学原理深入解析了汶川地震断层陡坎在遥感影像上的阴影形成与识别特征,明确了成像时刻和断坎产状对影像阴影的形成和断层陡坎识别能力的约束。结合影像成像特征与汶川地震同震地表破裂特征的应用分析,客观地认识了现有遥感影像在同震地表变形应用中的局限性,可为今后的应急航空遥感方案设计提供参考 相似文献
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天山全新世活动断裂及古地震研究 总被引：2，自引：0，他引：2
横亘亚洲腹地的天山山脉近代构造活动十分强烈。规模较大的全新世活动断裂有２０多条，多为近东西走向的倾滑型逆断裂，常与活动褶皱相伴生。活动褶皱为无根的断裂扩展褶皱和滑脱褶皱，它的生长是受地下活动的盲断裂所控制，往往是褶皱地震潜在的地区。天山古地震活动遗迹很多，归纳其标志有：多重断层陡坎、古断塞塘、崩积楔、填充楔、推覆楔、地震断错台地和断裂扩展褶皱等。近几年对１０条全新世活动断裂进行开挖研究，已取得大地 相似文献
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2008年5月12日汶川8.0级大地震发生在青藏高原东缘龙门山推覆构造带上,除映秀—北川断裂、灌县—江油断裂上各形成240 km和72 km 长的地表破裂带外,可能在成都平原西部的什邡市师古镇附近形成一条弱地表破裂带.成都平原内的地震地表破裂带与龙门山区的2条地震破裂带构成倾向北西的叠瓦状逆断裂地震地表破裂系统.野外调查发现,师古镇南肖家院—庆云庵建筑物严重破坏带、水渠跌水、地表褶皱、喷砂和地裂缝带走向30°,延伸长度约7.5 km.探槽开挖表明,地表地震褶皱陡坎下的地层发生弯曲变形,汶川地震使断层上盘的地面和最新地层褶皱隆起0.2 m.TC2探槽中的粘土层底面褶皱隆起0.4 m,它可能记录到汶川地震之前另外一次与汶川地震大小相当的古地震事件.浅层地震勘探资料表明,平原区出现地震地表破裂的位置不仅存在晚更新世活动断裂,而且伴生有第四纪活动褶皱. 相似文献
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近年来逆冲型破坏性地震频发,这对于逆冲型破裂的古地震研究方法提出了新的要求。由于逆断层角度的变化,在地震中可能表现出截然不同的破裂样式。通过对南天山大量古地震探槽开挖和古地震事件分析研究中发现,低角度逆断层的古地震具有一些常见的破裂类型。本文中挑选了位于南天山三个重要山前逆断裂褶皱带:西段柯坪推覆系、中段库车坳陷的秋里塔格褶皱带和东段焉耆盆地北缘和静逆断裂褶皱带的7个典型探槽剖面,对这类低角度逆断层的古地震进行变形模式、事件识别和位移量计算的总结归纳。低角度逆断层古地震破裂具有以下几种样式并具有各自识别古地震事件和计算位移量的方法:1一条断面对应一次事件的破裂形式,利用断面上断点位置识别古地震事件并判断事件的先后顺序。每个断面各自的位移量正好代表一次事件的位移量。2单条断面多次破裂的样式可以通过上下不同地层的位错量差异判断古地震事件,各个相邻地层之间的位错量差值代表古地震事件的位移量。3多条断面同时破裂的情况表现为多条断面被相同一套地层覆盖,事件位移量为多条断面的位错量之和。4挠曲变形和"推土机"作用是低角度逆断层古地震破裂常见的变形方式,这部分变形量不能忽略,可以通过线平衡和面平衡方法获得断层水平缩短量。 相似文献
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汶川M_S8.0地震发震断裂大地震原地重复现象初析 总被引：37，自引：8，他引：29
在历史记录中,成都和龙门山地区没有发生过类似汶川MS8.0地震强度的地震。那么,在地质记录中是否会存在类似震级的古地震遗迹?作者分别在中央和前山断裂中段的地表破裂带上4个地点开挖了探槽4个和剖面1个,并进行了断错地貌面的实测。文中从几个地点新老地貌面累计变形量、探槽揭露的古地震遗迹等方面讨论汶川地震发震断裂大地震原地重复现象存在的基本事实。结果表明:无论在中央断裂的小鱼洞、擂鼓镇还是前山断裂的白鹿镇、汉旺等地,汶川5.12地震之后Ⅱ级阶地断层陡坎与Ⅰ级阶地陡坎高度基本呈倍数关系,探槽揭露Ⅱ级阶地标志地层(黄砂土层)在断裂两盘的位差也是5.12地震的约2倍,显示在龙门山地区区域Ⅱ级阶地形成之后,汶川5.12地震发生之前,存在一次与汶川MS8.0地震地表变形规模相当的地震事件 相似文献
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地表破裂型逆断层地表缩短量计算方法探讨——以汶川M_S 8.0地震地表变形为例 总被引：8，自引：0，他引：8
合理估计逆断层地表破裂缩短量是全面认识同震地表变形参数的核心内容,目前还没有较成熟的方法。以汶川MS8.0地震地表破裂为例,尝试通过探槽开挖来研究逆断层水平缩短量的计算问题。在分析汶川地震同震变形的基础上,总结了3种陡坎的成因模式:断层断错地表型、挠曲型、断层与挠曲叠加型,并依据这些模型提出了一些水平缩短量的计算方法及其限制条件,以及如何理解逆断层地表破裂探槽开挖所揭示的信息。最后给出了汶川MS8.0地震白鹿中心学校和汉旺全新村两地点水平缩短量的求解过程及结论,计算得到白鹿中心学校探槽水平缩短量为(2.83±0.3)m,汉旺全新村探槽水平缩短量为(0.61±0.11)m 相似文献
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乌鲁木齐西山断裂组与地表破裂型逆断层古地震识别标志 总被引：3，自引：5，他引：3
乌鲁木齐西山断裂层组展布于北天山山前断展褶皱系与博格达推覆构造系的转换部位,为盆地向S推覆的构造,由4～5条长度十几公里至近30km的断层组成,其滑脱面埋深约11km。通过地质地貌调查、探槽开挖,结合深部构造特征分析,西山断裂组晚更新世中晚期有明显的活动。断层F1—F3最年轻的2次事件基本都被限制在距今(22.7±5.2)ka和40ka左右。而F4和西山断裂最年轻的事件被距今31.0ka和38.0ka的地层覆盖。这显示西山断裂组晚第四纪活动有分组和组合破裂的特征。断层F4和西山南缘断裂为一组,F1—F3为另一组。坎前堆积地层、断层与堆积地层的切错关系和不同间断面或标志地层在断层两侧的累积位差的突变,是识别地表破裂型逆断层古地震事件的重要标志。降低逆断层古地震识别的不确定性,关键在于识别事件的标志需要综合分析各种影响因素,有多证据的支持 相似文献
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龙门山山前疑似汶川M_S 8.0地震地表破裂的浅层地震反射调查 总被引：2，自引：0，他引：2
2008年5月12日发生在龙门山构造带的汶川MS8.0大地震是映秀-北川断裂突发错动的结果。此次地震不但使NE向的映秀-北川断裂和灌县-江油断裂发生了地表破裂,而且,在成都平原区的什邡、绵竹等地也出现了不同程度的地表裂缝、公路拱曲以及带状的喷砂冒水现象。此项探测研究以出现在什邡市师古镇附近的疑似地震地表破裂带为切入点,通过采用可控震源以及高精度的浅层地震反射勘探方法,获得了深度15～800m范围内高分辨率的地下结构和构造图像。结果表明,在地表破裂之下存在向平原区逆冲的隐伏断层和反向的逆冲断层,地震过程中隐伏逆断层的活动可能是近地表地层出现褶皱变形和地表破裂的主要原因 相似文献
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古地震研究的主要目标是识别或揭露地质地貌记录的大地震变形遗迹,确定大地震发生的时间、复发特征、同震位移量等参数。要实现这样的目标,探槽开挖地点能否完整记录晚第四纪发生的古地震事件、能否获取大量的测年样品以控制事件发生的年代、能否正确地识别这些事件等是关键,并直接关系到未来大地震危险性评价的可靠性。由于走滑断裂位移发生的特殊性,好的探槽研究地点并不普遍。文中在综合分析走滑断裂同震地表变形特征、影响因素的基础上,通过案例分析,总结出可能成为走滑断裂古地震研究和探槽开挖的候选地点,如洼地、盆地、槽谷、断塞塘、被同步位移连续错开的冲沟床、连续的坎前堆积地层和多级地貌面连续变形等。组合探槽或三维探槽应该是走滑断裂探槽布设的首选。跨断层微地貌位错、断错地层以及上覆更新地层、局部坎前堆积和裂缝充填堆积、不同地层单元沿断层面位移量的突然增加或降低、不同程度的弯曲变形、不同期次的古断塞塘(坑)堆积等,可以作为重要的事件识别依据。要降低古地震识别的不确定性,需要理顺研究程序,明确技术方案,逐一精心实施。认识和结论的得出需要反复推敲,并广泛讨论,同时需要注意细节以及各种信息的相互补充和印证。 相似文献
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中国大陆古地震研究的关键技术与案例解析(5)——断层隐形、尖灭与年轻事件识别 总被引：1，自引：0，他引：1
《地震地质》2015,(2)
断层隐形或尖灭现象在年轻事件影响的地层中较为突出,可能造成年轻事件识别的误判,增大地震危险性评价的不确定性。文中在前人相关研究成果的基础上,结合中国的研究实例,讨论断层隐形与年轻事件识别的问题。断裂在砂层、土壤、粉砂层、黄土、黏土质砂中的隐形比较普遍。在走滑、逆断层和正断层3种构造类型中走滑断层出现隐形的比例最高。汶川地震破裂带及其他一些探槽研究的案例显示,易"隐形"地层中年轻事件的识别需要从探槽开挖地点选择、探槽开挖方式、探槽信息的综合分析等相关技术入手。选择多韵律地层开挖探槽是避免断层隐形影响事件识别的关键;组合或3维探槽有利于减小断层局部隐形的影响;上下层位推延、粒度、色度以及土壤发育程度等综合分析是识别隐形断层的基本手段;显微构造、粒度和磁化率分析等是隐形断层识别的重要发展方向之一。 相似文献
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本文简要报导华北地区几个古地震实例:1.内蒙磴口西北地震毁坏的汉代古城废墟;2.宁夏平罗西北红果子沟长城错开及古地震断层陡坎;3.宁夏中宁古城子古地震断层及沙基液化变形;4.天水—宝鸡—常兴古地震黄土滑坡带;5.辽宁海城黑音寺山地震裂缝及岩崩;6. 山东临朐山旺湖相硅藻土层中地震引起的揉皱变形;7.江苏新沂嶂山闸古地震裂缝 相似文献
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安宁河断层与则木河断层是青藏高原东南川滇地块东边界断裂带的重要组成部分,晚第四纪以来变形样式主要以左旋走滑运动为主。安宁河断层走向近SN向,以冕宁为界分为南北两段,北段古地震复发周期500~700a,全新世以来左旋平均位移速率约4mm/a。南段的古地震研究程度较低,通过在月华一带开挖探槽及大量14C测年限定其大地震平均复发间隔为600~800a。则木河断层北接安宁河断层,全新世以来平均左旋位移速率为2.4~3.6mm/a,大地震复发周期约2 300a。对比安宁河断层与则木河断层的古地震行为,发现安宁河断层大地震复发间隔相对较短,平均左旋位移速率稍大,存在着古地震行为的不协调性。安宁河断层与则木河断层走向不一致、螺髻山的快速隆升以及安宁河断层南侧SN向展布的走滑断层系统等可能是造成安宁河-则木河断层古地震行为差异的原因。 相似文献
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As the boundary between the northern edge of the Tibetan plateau and the Tarim Basin, the active left-lateral strike-slip Altyn Tagh Fault (ATF) is a first-order structure accommodating the ongoing continental collision between India and Asia and extends from northwestern Tibet to eastern Gansu Province with a whole length of ~1 600km. It is regarded as one of the most active fault in Euro-Asia block and has been segmented eleven rupture segments. This study utilizes the high-resolution image data (Google Earth) in combination with detailed field investigation on the Aksay segment of the ATF to scan the gully offset by Trimble VX, which suggests that the latest earthquake offset is 6~7m. Through trenching and radiocarbon dating of charcoal samples, paleoseismic events of this segment are analyzed. The trench has revealed many different deformed and dislocated strata, which display four paleoseismic events. Combined with the previous research and using the progressive constraining method, we constrained the paleoseismic events in this segment, and the results suggest that the penultimate and the most recent event occurred~1180a BP and 507~230a BP, respectively. 相似文献
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PALEOSEISMIC RECORDS OF LARGE EARTHQUAKES ON THE CROSS-BASIN FAULT IN THE SALT LAKE PULL-APART BASIN AND CASCADE RUPTURE EVENTS ON THE HAIYUAN FAULT 
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下载免费PDF全文 Cascade rupture events often occur along large strike-slip fault zone.The 1920 AD M 81/2 earthquake ruptured all 3 segments of the Haiyuan Fault,and the Salt Lake pull-apart basin is the boundary between the west and middle segment of the fault.The data of trenching and drilling reveal 7 events occurring since last stage of late Pleistocene,and the two youngest events are associated with the historical records of 1092 AD (possibly) and 1920 AD respectively.These events are all large earthquakes with magnitude M>8,and the recurrence of them is characterized by earthquake clusters alternating with a single event.Now it is in the latest cluster which may last about 1000 years.Comparison of the paleoseismic sequence of this study and previous results reveals that the cross-basin fault in the Salt Lake pull-apart basin does not always rupture when cascade rupture events occur along the Haiyuan Fault,and likely ruptures only when the magnitude of the events is large (maybe M>8).Though there are many advantages in paleoseismic study in pull-apart basin,we should avoid getting the paleoseismic history of major strike-slip fault zones only depending on the rupture records of inner faults in pull-apart basins with large scale (maybe a width more than 3km). 相似文献
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THE PALEOSEISMIC SURFACE RUPTURE AT SOUTH OF CENTRAL ALTYN TAGH FAULT AND ITS TECTONIC IMPLICATION 下载免费PDF全文
下载免费PDF全文 SHAO Yan-xiu YUAN Dao-yang LIU-ZENG Jing Jerome Van der Woerd LI Zhi-gang WU Lei LIU Fang-bin 《地震地质》1979,42(2):435-454
In this study, we described a 14km-long paleoearthquakes surface rupture across the salt flats of western Qaidam Basin, 10km south of the Xorkol segment of the central Altyn Tagh Fault, with satellite images interpretation and field investigation methods. The surface rupture strikes on average about N80°E sub-parallel to the main Altyn Tagh Fault, but is composed of several stepping segments with markedly different strike ranging from 68°N~87°E. The surface rupture is marked by pressure ridges, sub-fault strands, tension-gashes, pull-apart and faulted basins, likely caused by left-lateral strike-slip faulting. More than 30 pressure ridges can be distinguished with various rectangular, elliptical or elongated shapes. Most long axis of the ridges are oblique(90°N~140°E)to, but a few are nearly parallel to the surface rupture strike. The ridge sizes vary also, with heights from 1 to 15m, widths from several to 60m, and lengths from 10 to 100m. The overall size of these pressure ridges is similar to those found along the Altyn Tagh Fault, for instance, south of Pingding Shan or across Xorkol. Right-stepping 0.5~1m-deep gashes or sub-faults, with lengths from a few meters to several hundred meters, are distributed obliquely between ridges at an angle reaching 30°. The sub-faults are characterized with SE or NW facing 0.5~1m-high scarps. Several pull-apart and faulted basins are bounded by faults along the eastern part of the surface rupture. One large pull-apart basins are 6~7m deep and 400m wide. A faulted basin, 80m wide, 500m long and 3m deep, is bounded by 2 left-stepping left-lateral faults and 4 right-stepping normal faults. Two to three m-wide gashes are often seen on pressure ridges, and some ridges are left-laterally faulted and cut into several parts, probably owing to the occurrence of repetitive earthquakes. The OSL dating indicates that the most recent rupture might occur during Holocene.
Southwestwards the rupture trace disappears a few hundred meters north of a south dipping thrust scarp bounding uplifted and folded Plio-Quaternary sediments to the south. Thrust scarps can be followed southwestward for another 12km and suggest a connection with the south Pingding Shan Fault, a left-lateral splay of the main Altyn Tagh Fault. To the northeast the rupture trace progressively veers to the east and is seen cross-cutting the bajada south of Datonggou Nanshan and merging with active thrusts clearly outlined by south facing cumulative scarps across the fans. The geometry of this strike-slip fault trace and the clear young seismic geomorphology typifies the present and tectonically active link between left-lateral strike-slip faulting and thrusting along the eastern termination of the Altyn Tagh Fault, a process responsible for the growth of the Tibetan plateau at its northeastern margin. The discrete relation between thrusting and strike-slip faulting suggests discontinuous transfer of strain from strike-slip faulting to thrusting and thus stepwise northeastward slip-rate decrease along the Altyn Tagh Fault after each strike-slip/thrust junction. 相似文献
Southwestwards the rupture trace disappears a few hundred meters north of a south dipping thrust scarp bounding uplifted and folded Plio-Quaternary sediments to the south. Thrust scarps can be followed southwestward for another 12km and suggest a connection with the south Pingding Shan Fault, a left-lateral splay of the main Altyn Tagh Fault. To the northeast the rupture trace progressively veers to the east and is seen cross-cutting the bajada south of Datonggou Nanshan and merging with active thrusts clearly outlined by south facing cumulative scarps across the fans. The geometry of this strike-slip fault trace and the clear young seismic geomorphology typifies the present and tectonically active link between left-lateral strike-slip faulting and thrusting along the eastern termination of the Altyn Tagh Fault, a process responsible for the growth of the Tibetan plateau at its northeastern margin. The discrete relation between thrusting and strike-slip faulting suggests discontinuous transfer of strain from strike-slip faulting to thrusting and thus stepwise northeastward slip-rate decrease along the Altyn Tagh Fault after each strike-slip/thrust junction. 相似文献
20.
WANG Ming-ming HE Yu-lin LIU Shao WANG Shi-yuan MA Chao ZHANG Wei JIA Zhao-liang 《地震地质》2018,40(4):738-752
The Ganzi-Yushu Fault, the boundary of Bayan Har active tectonic block, Qiantang active tectonic block and Sichuan-Yunan active tectonic block, is a sinistral strike-slip fault zone with intensive Holocene activity. Thus, the study of activity characteristics and rupture behavior of paleoearthquakes in the late Quaternary on the Ganzi-Yushu Fault is of fundamental importance for understanding the future seismic risk of this fault. The southeast section of Ganzi-Yushu Fault is made up of three segments of Ganzi, Manigange and Dengke, where a MS7.3 earthquake in 1866, a MS7.7 earthquake in 1854 and a MS7.3 in 1896 occurred, respectively. There is still lack of in-depth study on the active features and the cascading rupture possibility of these segments, which hindered the evaluation of seismic risk for the southeast section of Ganzi-Yushu Fault. By the means of field geological survey and micro topography measurement, this paper studied the geological and geomorphological features of the southeast section of the Ganzi-Yushu Fault. The results show that the Ganzi and Dengke segments show obvious extension movement, in addition to the left-lateral movement. For Manigange segment, the characteristics of the movement are mainly left-lateral strike-slip and thrusting, and the maximum vertical displacement of the Holocene strata is greater than 2m. In part areas, the movement is normal faulting, which perhaps relates to the left stepping zone in the local stress environment. Therefore, combining the research results such as the fracture distribution in different motion characteristics, rupture behavior of paleoearthquakes, and the distribution of historical earthquake surface ruptures, we divide the southeast section of Ganzi Yushu Fault into Ganzi, Manigange and Dengke segment, and consider the Yakou and the Dengke Basin as the stepovers and the segments' boundaries. As the small scale of impermanent barriers including Dengke Basin and the ridge near Yakou, of which the width is about 1~2km, they may be broken through in great earthquake rupture in future. A trench was excavated in Zhuqing township to investigate the paleoearthquakes on the Manigange segment, radiocarbon dating was employed and 3 paleoseismic events were revealed in the Zhuqing trench, which are the seismic events occurring respectively at 3875~3455BC, after 775BC, and the latest one that ruptured the surface. Compared with the previous results of paleoseismology in the southeast section of Ganzi-Yushu Fault, it is found that the paleoseismic events in the Manigange segment are obviously different with that in Ganzi segment and Dengke segment. Due to the lack of sufficient data on the southeast section of the Ganzi-Yushu Fault, it still needs further discussion whether the cascade-rupturing between these segments exists. 相似文献