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1.
2008年5月12日的汶川8.0级地震使龙门山断裂带形成了3条同震地表破裂带,这表明有多条活动断层同时参与地震破裂,其过程复杂,现象丰富。本文对小鱼洞地表破裂带及其与另2条地表破裂带的交汇区域进行了野外调查,并对小鱼洞地表破裂带的活动性质和展布特征进行了分析。小鱼洞地表破裂带位于彭州市小鱼洞镇附近,是汶川8.0级地震形成的一条走向NW的逆冲并具有左旋走滑分量的同震地表变形带。调查结果显示,小鱼洞地表破裂带表现出明显的分段性特征：小鱼洞镇一带的中段,逆冲量和走滑量最大;小鱼洞镇向东南方向延伸的南段,逆冲量和走滑量逐渐变小;小鱼洞镇向西北方向进入山区的北段,则表现为以逆冲为主的活动性质。 相似文献
2.
为剖析2008年汶川MS8.0地震对后期地震的影响及发震区域构造应力场特征,首先利用2008年5月12日—2013年4月19日汶川地震及其邻区的1660条震源机制解,同时采用同一地震多个震源机制中心解的方法筛去重复地震事件的震源机制解,最终获得911个震源机制解。其次,通过网格搜索法分段反演出区域构造应力场。结果显示:东北区主要受WNW-ESE向的挤压,西南区受W-E向的挤压,中区受WSW-ENE向的挤压。西南到东北主压应力轴方向有所变化,这可能与龙门山地区受到来自印度板块北北东方向的俯冲推挤、四川盆地的阻挡和巴颜喀拉块体东南向挤压的联合作用有关。然后,基于USGS给出的汶川MS8.0地震的破裂模型,计算出该地震对附近强震的触发关系,结果表明,本次汶川地震对同属龙门山断裂西南端的芦山地震触发作用明显,对位于东昆仑断裂上的玛多地震也有一定的触发作用。最后,计算汶川MS8.0地震对周围断层的同震库仑应力变化,发现本次地震造成龙门山断裂南北两端、秦岭南缘断裂、鲜水河断裂东南端、东昆仑断裂、白玉断裂的库仑破裂应力增加,龙门山断裂南北两端和秦岭南缘断裂增加最为明显,对分析地震危险性有一定的参考意义。 相似文献
3.
本文利用2013年芦山M_S7.0级地震同震GPS数据反演了芦山断层几何与断层滑动分布,结果表明:芦山地震发震断层具有南陡北缓、上陡下缓的特征,低倾角的区域位于发震断层北段且靠近映秀断层的一侧;滑动分布模型的最大滑动量为0.82m,其深度为13.67km与小震发生集中平均深度12.5km接近.我们选取1998—2014年龙门山断裂带区域地壳形变观测数据,拟合获得了龙门山断裂带走向方向上的速度分量,发现在汶川M_S8.0地震与芦山M_S7.0地震之间宽度约30km破裂空区,龙门山断裂带西南段与东北段的形变分量以破裂空区为界方向相反.断裂带东北段(汶川地震主要发震断层)的形变分量方向与断层右旋走滑运动方向一致,而在断裂带西南段(芦山地震发震断层)的形变分量方向与断层左旋走滑运动方向一致.芦山地震走滑方向与汶川地震走滑方向相反是因为该断裂带构造运动在特有几何构造下受青藏高原东南向挤压,遇龙门山中段岩石圈楔状构造的阻挡,在汶川M_S8.0地震与芦山M_S7.0地震间的地震空区,形成了构造运动向其两侧分流的结果. 相似文献
4.
利用区域GPS和水准测量资料,结合地震构造背景的分析,本文研究2008年汶川8.0级地震前横跨龙门山断裂带地区的震间地壳形变,探讨引起这种形变的活动构造与动力学模式,并由此认识汶川地震的孕育与成因机制.主要结果表明：1997～2007年期间,自龙门山断裂带中段朝北西约230 km的地带内存在垂直于断裂的水平缩短变形、以及平行于断裂的水平右旋剪切变形,缩短率为1.3×10-8/a （即：0.013 mm/km/a）,角变形速率为2.6×10-8/a;同一地带在1975～1997年期间还表现出垂直上隆变形,上隆速率在龙门山前山断裂与中央断裂之间仅0.6 mm/a,而至龙门山后山断裂及其以西达2～3 mm/a.这些反映了在汶川地震之前至少10～30余年,龙门山断裂带中段的前山与中央断裂业已闭锁、并伴有应变积累.造成这种形变的主要原因是：以壳内的低速层为“解耦”带,巴颜喀拉地块上地壳朝南东的水平运动在四川盆地西缘受到华南地块的阻挡、转换成龙门山断裂带中段的逆冲运动;由于该断裂段的震间闭锁,致使西侧的巴颜喀拉地块的上地壳发生横向缩短以及平行断裂的右旋剪切变形.然而,龙门山断裂带北段在1997～2007年期间除了有大约0.9 mm/a的右旋剪切变形外,横向的缩短变形极微弱,这可能与该断裂段西侧的岷江、虎牙、龙日坝等断裂带吸收了巴颜喀拉地块朝东水平运动的大部分有关.另外,汶川地震前,横跨龙门山断裂带中段与北段的地壳形变特征的差异,与汶川地震时能量释放的空间分布吻合. 相似文献
5.
为了了解2008年5月12日四川汶川MS8.0地震发生的地震活动背景,本文综合历史与现代地震资料,从南北地震带中段及其邻区的视野研究了汶川地震前1~2千年的强震活动性,以及震前20年的地震活动性背景.结果主要表明：（1）至少在2008年之前的1100~1700年中,龙门山断裂带未发生M≥7的地震,相对其南、北两侧的其他活动断裂带（或段）形成一个地震空区,2008年汶川MS8.0地震发生在该空区中;（2）17世纪以来,在由龙门山断裂带大部分地区、川北岷江-虎牙断裂带以及甘南文县-武都断裂带组成的巴颜喀拉块体东边界上共发生了12次M=6.5~8.0地震,显示出一个已持续了近400年、逐渐加速的应变能释放过程,2008年汶川MS8.0地震属于该过程中两次巨大地震之一;（3）汶川地震前20年,龙门山断裂带中、南段不存在背景地震活动的平静,反而显示出比曾经发生过1879年MS8地震的甘南文县-武都断裂带还略高的地震活动背景水平;（4）2008年汶川地震的强度远远超出龙门山断裂带的历史最大地震,说明仅基于数百年至一、两千年的历史地震记载,远不足以正确评估较低滑动速率的、大型活动断裂带的潜在地震危险性. 相似文献
6.
为了研究与总结2008年5月12日汶川8.0级地震前GPS与跨断层资料反映的龙门山断裂带及其周边地区的运动、构造变形、应变积累演化过程,以及汶川地震临震阶段可能的物理机制,本文综合1999~2007期GPS速度场、1999~2008年大尺度GPS基线时间序列、1985~2008年跨断层短水准等资料进行了相关分析与讨论。结果表明:(1)GPS速度剖面结果显示,宽达500km的川西高原在震前有明显的连续变形,而四川盆地一侧和跨龙门山断裂带基本没有变形趋势,表明震前川西高原在持续不断地为已经处于闭锁状态的龙门山断裂带提供能量积累。(2)GPS应变率结果显示,震前龙门山断裂带中北段的NW侧EW向挤压变形明显,变形幅度从远离断裂带较大到靠近断裂带逐渐减小,而断裂带变形微弱;龙门山断裂带西南段周边形成了显著的EW向挤压应变集中区,应变积累速率明显大于中北段。(3)断层闭锁程度反演结果显示,除了汶川地震的震源位置闭锁相对较弱,且西南段有大概20km宽度断层在12~22.5km深度为蠕滑状态以外,震前整条龙门山断裂基本处于强闭锁状态。(4)大尺度GPS基线结果显示,跨南北地震带区域的NE向基线从2005年开始普遍出现压缩转折,反映NE向地壳缩短的相对运动增强。(5)跨断层短水准场地结果显示,震前年均垂直变化速率和形变累积率很低,表明断层近场垂向活动很弱、闭锁较强。通过以上分析认为,在相对小尺度的地壳变形中,震前龙门山断裂带深浅部均处于强闭锁状态,断裂带水平与垂直变形都很微弱,这可能经历了一个缓慢的过程,而且越是临近地震的发生,微弱变形的范围可能越大;在相对大尺度的地壳变形中,震前龙门山断裂带西侧的巴颜喀拉块体东部地区经历了地壳缓慢且持续的缩短挤压变形,为龙门山断裂带应变积累持续提供了动力支持。 相似文献
7.
Based on GPS velocity during 1999-2007, GPS baseline time series on large scale during 1999-2008 and cross-fault leveling data during 1985-2008, the paper makes some analysis and discussion to study and summarize the movement, tectonic deformation and strain accumulation evolution characteristics of the Longmenshan fault and the surrounding area before the MS8.0 Wenchuan earthquake, as well as the possible physical mechanism late in the seismic cycle of the Wenchuan earthquake. Multiple results indicate that:GPS velocity profiles show that obvious continuous deformation across the eastern Qinghai-Tibetan Plateau before the earthquake was distributed across a zone at least 500km wide, while there was little deformation in Sichuan Basin and Longmenshan fault zone, which means that the eastern Qinghai-Tibetan Plateau provides energy accumulation for locked Longmenshan fault zone continuously. GPS strain rates show that the east-west compression deformation was larger in the northwest of the mid-northern segment of the Longmenshan fault zone, and deformation amplitude decreased gradually from far field to near fault zone, and there was little deformation in fault zone. The east-west compression deformation was significant surrounding the southwestern segment of the Longmenshan fault zone, and strain accumulation rate was larger than that of mid-northern segment. Fault locking indicates nearly whole Longmenshan fault was locked before the earthquake except the source of the earthquake which was weakly locked, and a 20km width patch in southwestern segment between 12km to 22.5km depth was in creeping state. GPS baseline time series in northeast direction on large scale became compressive generally from 2005 in the North-South Seismic Belt, which reflects that relative compression deformation enhances. The cross-fault leveling data show that annual vertical change rate and deformation trend accumulation rate in the Longmenshan fault zone were little, which indicates that vertical activity near the fault was very weak and the fault was tightly locked. According to analyses of GPS and cross-fault leveling data before the Wenchuan earthquake, we consider that the Longmenshan fault is tightly locked from the surface to the deep, and the horizontal and vertical deformation are weak surrounding the fault in relatively small-scale crustal deformation. The process of weak deformation may be slow, and weak deformation area may be larger when large earthquake is coming. Continuous and slow compression deformation across eastern Qinghai-Tibetan Plateau before the earthquake provides dynamic support for strain accumulation in the Longmenshan fault zone in relative large-scale crustal deformation. 相似文献
8.
2013年芦山M_S7.0地震产生的静态库仑应力变化及其对余震空间分布的影响 总被引：5，自引：0，他引：5
2013年4月20日芦山MS7.0地震发生在龙门山断裂带的西南段,距2008年汶川MS8.0地震仅约85km,时间上仅相隔5年.首先计算了汶川地震的静态库仑应力变化对本次芦山地震的影响,得出芦山地震是由汶川地震触发造成的(库仑应力上升了0.012 MPa);进一步计算了芦山地震与汶川地震这两次大地震共同产生的静态库仑应力变化.结果表明,芦山地震的余震受前面两次大地震的共同影响,而不仅仅是芦山地震单独作用的结果,超过85%的余震发生在两次地震共同产生的静态库仑应力变化增大的地方,而芦山地震本身触发不了本次的余震序列(仅48.7%的余震位于主震所产生的应力加载区).此外,计算结果表明芦山地震本身对周边断层影响较小,仅龙门山断裂带的东北段受到一定的加载作用;而由于汶川地震的作用,安宁河断裂、大凉山断裂、马尔康断裂、岷江断裂和虎牙断裂呈卸载趋势,仅鲜水河断裂东南段和龙门山断裂中段受到加载作用,这均会加速断层上新地震的发生. 相似文献
9.
利用1999-2007和2009-2011年中国大陆GPS水平速度场数据, 采用DEFNODE(反演计算弹性岩石圈块体旋转、 应变和块体边界断层闭锁或同震滑动的Fortran程序)负位错反演程序估算了芦山地震前龙门山断裂带的三维闭锁程度, 并结合剖面结果分析了断层深浅部变形特征. GPS反演结果表明, 1999-2007年, 龙门山断裂中北段(闭锁比例为0.99)处于强闭锁(本文将闭锁比例大于0.97的称为强闭锁)状态; 龙门山断裂南段地表以下深度16 km内为强闭锁, 深度16-21 km处闭锁比例降低为0.62, 深度21-24 km处整条断裂逐渐转变为蠕滑状态. 2009-2011年, 即汶川地震后, 龙门山断裂中北段处于震后蠕滑状态; 龙门山断裂南段深度16-21 km处闭锁比例降低为0.45, 其它位置闭锁程度保持不变. GPS剖面结果显示, 2009-2011年, 即汶川地震后, 龙门山断裂中北段为逆冲兼右旋走滑运动; 而南段断层不能自由滑动、 变形宽度较大. 综合分析认为, 汶川地震时, 龙门山断裂南段并没有发生破裂, 一直处于较强的闭锁状态, 汶川地震的发生又加速了芦山地震的孕育进程; 由于龙门山断裂带南段的闭锁深度较中北段浅, 因此芦山地震较汶川地震强度低、 震级小、 破裂范围窄. 相似文献
10.
本研究基于分层黏弹介质模型,考虑同震位错效应和震后黏滞松弛效应,分析巴颜喀拉地块东端1976年松潘地震序列、2008年汶川8.0级地震、2013年芦山7.0级地震和2017年九寨沟7.0级地震等多次大地震的可能存在的触发关系,计算大地震引起的周边各主要断裂的库仑应力变化.结果显示,1976年松潘地震序列各次地震间关系密切,存在明显的相继触发作用;综合考虑同震和震后效应,汶川8.0级地震对同属于龙门山断裂带的芦山7.0级地震有触发作用,且震后效应影响不可忽略;1976年地震序列,特别是1976年8月16日7.2级地震促进了2017年8月8日九寨沟7.0级地震的发生;汶川地震对九寨沟地震的影响研究中,采用不同的汶川地震同震位错模型,计算结果有差异.综合考虑多次大地震对周边断裂带的影响,龙门山断裂带南段、鲜水河断裂带中南段、平武—青川断裂北段、灌县—安县断裂北段、文县断裂的累积库仑应力增加显著,巴颜喀拉地块东端的东昆仑断裂带东段、迭部—白龙江断裂带西段以及金沙江断裂带库仑应力亦有所增加.综合考虑各重要断裂带已有的大地震危险性分析结果和库仑应力变化计算结果,龙门山断裂带南段、鲜水河断裂带中南段、东昆仑断裂带玛沁—玛曲段和金沙江断裂带的发震紧迫性有所增强,需引起关注. 相似文献
11.
THE RESEARCH OF THE SEISMOGENIC STRUCTURE OF THE LUSHAN EARTHQUAKE BASED ON THE SYNTHESIS OF THE DEEP SEISMIC DATA AND THE SURFACE TECTONIC DEFORMATION 
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下载免费PDF全文 WANG Lin ZHOU Qing-yun WANG Jun LI Wen-qiao ZHOU Lian-qing CHEN Han-lin SU Peng LIANG Peng 《地震地质》2016,38(2):458-476
The seismogenic structure of the Lushan earthquake has remained in suspensed until now. Several faults or tectonics, including basal slipping zone, unknown blind thrust fault and piedmont buried fault, etc, are all considered as the possible seismogenic structure. This paper tries to make some new insights into this unsolved problem. Firstly, based on the data collected from the dynamic seismic stations located on the southern segment of the Longmenshan fault deployed by the Institute of Earthquake Science from 2008 to 2009 and the result of the aftershock relocation and the location of the known faults on the surface, we analyze and interpret the deep structures. Secondly, based on the terrace deformation across the main earthquake zone obtained from the dirrerential GPS meaturement of topography along the Qingyijiang River, combining with the geological interpretation of the high resolution remote sensing image and the regional geological data, we analyze the surface tectonic deformation. Furthermore, we combined the data of the deep structure and the surface deformation above to construct tectonic deformation model and research the seismogenic structure of the Lushan earthquake. Preliminarily, we think that the deformation model of the Lushan earthquake is different from that of the northern thrust segment ruptured in the Wenchuan earthquake due to the dip angle of the fault plane. On the southern segment, the main deformation is the compression of the footwall due to the nearly vertical fault plane of the frontal fault, and the new active thrust faults formed in the footwall. While on the northern segment, the main deformation is the thrusting of the hanging wall due to the less steep fault plane of the central fault. An active anticline formed on the hanging wall of the new active thrust fault, and the terrace surface on this anticline have deformed evidently since the Quaterary, and the latest activity of this anticline caused the Lushan earthquake, so the newly formed active thrust fault is probably the seismogenic structure of the Lushan earthquake. Huge displacement or tectonic deformation has been accumulated on the fault segment curved towards southeast from the Daxi country to the Taiping town during a long time, and the release of the strain and the tectonic movement all concentrate on this fault segment. The Lushan earthquake is just one event during the whole process of tectonic evolution, and the newly formed active thrust faults in the footwall may still cause similar earthquake in the future. 相似文献
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NUMERICAL SIMULATION OF DEFORMATION MOVEMENT AND STRESS ACCUMULATION IN LONGMENSHAN AND ITS ADJACENT FAULTS BEFORE WENCHUAN EARTHQUAKE 下载免费PDF全文
下载免费PDF全文 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. 相似文献
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2008年5月12日四川省汶川县发生了MS8.0强烈地震.发震断层是龙门山断裂带的映秀—北川断裂.分析震前的GPS速度场发现,从巴颜喀拉块体西部到龙门山断裂带沿大约N103°E方向的缩短速率为13.0 mm/a,龙门山断裂带的右旋走滑速率1.1 mm/a,断裂带处于闭锁状态.四川盆地沿大约N103°E方向有少量的压缩变形,而沿SW方向有少量的拉张变形.同震位移场显示,这次地震可能是巴颜喀拉块体SE向逆冲与四川盆地NW向俯冲同时发生的.应变场分析发现,震前震中区的主压与主张应变率分别为-30.840×10-9/a与13.956×10-9/a,主压应变轴N105.4°E与震源机制解得到的主压应力轴的方向N103°E一致.由本文提出的应力-应变机制得到的断层滑动方向和走向与地表破裂调查和震源机制解得到的结果一致.印度、太平洋和菲律宾海板块与欧洲板块的相互作用是龙门山断裂带积累弹性应变能和孕育汶川地震的长期作用力.苏门达腊大地震使青藏高原和华南块体的相互作用加强,促进了汶川地震的发生. 相似文献
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运用非连续变形分析法与三维有限元法相结合的方法,以GPS资料作为位移速率和震源机制的约束条件,通过数值模拟研究了青藏高原及其东侧邻区构造地块的运动、变形、相互作用及其与近30年来发生于该区的大地震之间的关系。研究中引入了以应力与摩擦强度的比值定义的断层“失稳危险度”,通过数值模拟计算得到了研究区地壳块体边界断层的失稳危险度分布。结果表明,失稳危险度高的地段与近期该区发生的MS≥7.0地震所在的位置基本一致,其中龙门山断裂带上包括汶川和芦山大地震的发震断层均为失稳危险度最高值地区。计算得到的应变率强度分布图显示,青藏高原东部边缘整条地带均为应变率强度的陡变带,特别是以龙门山断裂带上的陡变最为明显,其西侧应变率强度为东侧的近4倍,而且,这个带位于宽度相同、走向与龙门山断裂带走向相一致的高应变能密度带中,表明这两次大地震前,作为其发震断层的龙门山断裂带已积累了相当高的应变能,失稳危险度高,处于力学上的不稳定状态。模拟计算得到在上地壳层中,2001年昆仑山口西MS8.1地震引起汶川、芦山地震发震断层的库仑破裂应力增加约0.016 MPa,相当于龙门山断裂带约两年的应力积累,也就是说,使汶川、芦山地震发震断层的失稳破裂提前了约两年。 此外,关于2008年汶川MS8.0地震的模拟计算表明,汶川地震的发生也使包括芦山地震发震断层的龙门山断裂带西南段和东昆仑断裂带东南端的库仑破裂应力增大,应变能积累增强,这说明汶川MS8.0地震的发生对已处于失稳危险度较高状态的2013年芦山地震和2017年九寨沟地震发震断层的提前失稳破裂起到了促进作用。 相似文献
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利用1999—2007期和2009—2013期中国大陆GPS速度场数据,采用DEFNODE负位错反演程序估算了川滇菱形块体东边界——鲜水河—安宁河—则木河—小江断裂带在汶川地震前后的断层闭锁程度和滑动亏损空间分布动态变化特征,讨论了汶川地震对该断裂系统的影响范围和程度,并结合b值空间分布和地震破裂时-空结果分析了断裂系统的强震危险段.结果表明,汶川地震前鲜水河断裂最南端为完全闭锁(闭锁深度25km),中南段地表以下10~15km深度为强闭锁状态,中北段基本处于蠕滑状态;安宁河断裂最南端闭锁很弱,其余位置闭锁深度为10~15km;则木河断裂除最南端闭锁较弱以外,其余位置基本为完全闭锁;小江断裂在巧家以南、东川以南、宜良附近、华宁以北等四处位置闭锁较弱,其余位置为强闭锁.10年尺度的GPS速度场反演所得断层闭锁程度所指示的强震危险段,主要为鲜水河断裂道孚—八美段、安宁河断裂中段、则木河断裂中北段、小江断裂北段东川附近、小江断裂南段华宁—建水段,该结果与地质尺度的断层地震空区和30年尺度的b值空间分布所指示的危险段落具有一致性.汶川地震后断裂带远、近场速度分布和块体运动状态发生变化,这种区域地壳运动调整使得负位错模型反演得到的断裂带闭锁情况发生一定变化.汶川地震前后川滇菱形块体东边界平行断层滑动亏损速率均为左旋走滑亏损,且在安宁河断裂北端、则木河断裂中北段滑动亏损速率最大;除鲜水河断裂中南段与最南端和小江断裂东川附近以外,其余断裂震后滑动亏损速率均有所增加.垂直断层滑动亏损速率既有拉张亏损也有挤压亏损,且鲜水河断裂最南端由震前挤压转变为震后拉张,其余断裂除了安宁河断裂和小江断裂中段与最北端存在挤压滑动亏损速率外均为拉张速率. 相似文献
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龙门山断裂带沿倾向和走向具有明显的分带性和分段性特征,通常以4条主干断裂为界将龙门山断裂带自西向东分为5条构造带,但是对沿走向的分段性特征仍未达成共识.本文利用四川区域地震台网记录的汶川地震后近10年的波形数据,采用全波形反演获取了龙门山断裂带1495个M≥3的震源机制解.通过“滑动窗”扫描方法提取不同地震类型的数量沿龙门山断裂带走向的变化曲线,据此将龙门山断裂带的震源区划分为S1—S9段.根据反演的震源机制解,进一步采用阻尼线性反演技术求取龙门山断裂带高分辨率的构造应力场信息,从地震类型、断面结构和构造应力场等角度探讨龙门山断裂带的分段性特征.结果表明:(1)地震类型存在明显的分段性特征.其中S1的逆冲型地震比例最高,S8的走滑型地震比例最高,S9的正断型地震比例最高.汶川地震后龙门山断裂带可能存在差异性断层调整运动,且余震晚期沿断裂带走向普遍存在应力的补充和协调,芦山地震的发生可能还对S2造成了应力扰动.汶川主震附近及余震区远端经历了更长的震后调整过程,且余震区远端S9具有更复杂、强度更高的震后调整过程.(2)断面结构存在明显的分段性特征.断面结构揭示汶川主震附近和余震区远端的隐伏断裂,以及虎牙断裂南端参与了汶川余震活动.断面倾角与走滑分量具有较好的一致性,在具有明显逆冲分量的分段断面倾角主要分布在50°~70°,而在具有明显走滑分量的分段断面倾角基本在60°以上,且断面倾角增大与汶川余震带宽度收缩变窄相吻合.(3)龙门山断裂带的应力环境非常复杂.σ1方向的分段性差异导致了汶川—芦山地震空区的地壳撕裂和地幔物质上涌、汶川主震附近和余震区远端的隐伏断裂活动以及虎牙断裂南端大量的逆冲型地震.结合构造应力场与大地测量资料认为,龙门山的隆升主要是受构造应力场作用下的上地壳缩短增厚所致. 相似文献
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Influence of 2008 Wenchuan earthquake on earthquake occurrence trend of active faults in Sichuan-Yunnan region 下载免费PDF全文
下载免费PDF全文 The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displacement is inverted from the deformation field in the 3-D geometric model. While the faults' slip velocities are inverted from GPS and leveling data, which can be used as the long-term slip vector. After the potential dislocation displacements are projected to long-term slip direction, we have got the influence of Wenchuan earthquake on active faults in Sichuan-Yunnan region. The results show that the northwestern segment of Longmenshan fault, the southern segments of Xianshuihe fault, Anninghe fault, Zemuhe fault, northern and southern segments of Daliangshan fault, Mabian fault got earthquake risks advanced of 305, 19, 12, 9.1 and 18, 51 years respectively in the eastern part of Sichuan and Yunnan. The Lijiang-Xiaojinhe fault, Nujiang fault, Longling-Lancang fault, Nantinghe fault and Zhongdian fault also got earthquake risks advanced in the western part of Sichuan-Yunnan region. Whereas the northwestern segment of Xianshuihe fault and Xiaojiang fault got earthquake risks reduced after the Wenchuan earthquake. 相似文献
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利用川西流动地震台阵、汶川地震震后应急台网记录到的P波到时资料,对2008年5月至2008年10月期间发生的汶川地震余震序列应用双差层析成像方法进行了地震震源和三维P波速度结构的联合反演.结果显示,联合反演获得的地震重定位结果与基于一维地壳参考模型的双差定位方法结果相近;研究区15 km以上速度结构与地表断裂分布密切相关,20 km以下深度呈现北东向和北西向交错结构.汶川地震破裂带南段龙门山断裂带之间上地壳呈现高速异常,速度结构的非均匀变化是控制余震分布和主震破裂传播的主要因素;联合反演结果给出了小鱼洞-理县方向存在隐伏断裂的速度结构证据,同时发现,破裂带北东段可能沿新发断裂扩展;结果确认了汶川地震起始段的高角度逆冲断裂特征,也确认了前山断裂和中央断裂在约20 km深度合并到脆韧转换带的特征. 相似文献
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THRUST OF THE SOUTHERN LONGMENSHAN FAULT IN THE LATE QUATERNARY REVEALED BY RIVER LANDFORMS 下载免费PDF全文
下载免费PDF全文 The Longmenshan fault zone is divided into three sections from south to north in the geometric structure. The middle and northern segments are mainly composed of three thrust faults, where the deformation of foreland is weak. The geometric structure of the southern segment is more complex, which is composed of six fault branches, where the foreland tectonic deformation is very strong. The Wenchuan MS8.0 earthquake occurred in the middle of the Longmenshan in 2008, activating the bifurcation of two branches, the Yingxiu-Beichuan and the Guixian-Jiangyou faults. In 2013, the Lushan MS7.0 earthquake occurred in the southern Longmenshan, whose seismogenic structure was considered to be a blind fault. After the Lushan earthquake, the seismic hazard in the southern Longmenshan has been widely concerned.
At present, the studies on active tectonics in the southern Longmenshan are limited to the Dachuan-Shuangshi and the Yanjing-Wulong faults. The Qingyi River, which flows across the southern Longmenshan, facilitates to study fault slip by the deformation of river terraces. Based on satellite imagery and high-resolution DEM analysis, we measured the fluvial terraces along the Qingyi river in detail. During the measurement, the Sichuan network GPS system (SCGNSS)was employed to achieve a precision of centimeter grade. Besides, the optical luminescence dating (OSL)method was employed to date the terraces' ages. And the late Quaternary activities of the six branch faults in the southern Longmen Shan were further analyzed.
The Gengda-Longdong, Yanjing-Wulong and the Xiao Guanzi faults (west branch of the Dachuan-Shuangshi fault)all show thrust slip and displaced the terrace T2. Their average vertical slip rates in the late Quaternary are 0.21-0.30mm/a, 0.12-0.21mm/a and 0.10-0.12mm/a, respectively. Since the Late Quaternary, vertical slip of the east branch of the Dachuan-Shuangshi fault was not obvious, and the arc-like Jintang tectonic belt was not active. Crustal shortening rate of the southern Longmenshan thrust fault zone in the late Quaternary is 0.48-0.77mm/a, which equals about half of the middle segment of the Longmenshan. Based on the previous study on the tectonic deformation of the foreland, we consider that the foreland fold belt in the southern Longmenshan area has absorbed more than half of the crustal shortening. The three major branch faults in the southern Longmenshan are active in the late Quaternary, which have risk of major earthquakes. 相似文献