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Magnetic fabrics in fault-related fold and its relation with finite strain: an example from Mingjiang thrust structures in Western Sichuan
Jia Dong,Chen Zhuxin,Luo Liang,Hu Qianwei,Jia Qiupeng,
Jia Dong
,Chen Zhuxin,Luo Liang,Hu Qianwei and Jia Qiupeng

自然科学进展 , 2007,
Abstract: The anisotropy of magnetic susceptibility (AMS) is a quick, effective and sensitive technique used to measure the weakly deformed sedimentary rocks, and also a reliable method to reveal the deforming mechanisms of fault-related folds. In Longmenshan front belt, a typical cross-section of fault-related folds is chosen to study the AMS. A total of 224 oriented specimens have been drilled at 23 different sampling sites which were distributed at the key structural positions of this structural section developed in the Xujiahe formation of the upper Triassic. Six elementary types of magnetic fabrics are recognized and established through this AMS study: Da sedimentary fabric; 2) an initial deformation fabric; 3) a pencil structure fabric; 4) a weak cleavage fabric; 5) a strong cleavage fabric; 6) a stretching lineation fabric. It has been found that most of magnetic fabrics are characterized by fabrics of weak deformation which belong to the pure-shear results of a pre-folding layer parallel shortening (LPS). In the fault-bend fold, almost all magnetic fabrics are the initial deformation fabrics of weak deformation, and denote that the deformation in the forelimb is stronger than that in the backlimb and no finite strain is shown in the footwall. While in the fault-propagation fold, finite strains are concentrated in the trishear zone where magnetic fabric results are approximately consistent with the estimated consequences of the kinematic model. The tectonic stress field indicated by the magnetic fabrics is basically the same along the whole structural section and shows a NW to SE compression and shortening which is accordant with the regional compressive stress field of the Longmenshan fold-thrust belt.
Fine seismic structure under the Longmenshan fault zone and the mechanism of the large Wenchuan earthquake
龙门山断裂带地壳精细结构与汶川地震发震机理

LEI Jian-She,ZHAO Da-Peng,SU Jin-Rong,ZHANG Guang-Wei,LI Feng,
雷建设

地球物理学报 , 2009,
Abstract: In this study we used a large number of P-wave arrival times recorded by the Sichuan permanent and portable seismic stations during January 2001 and June 2008 to obtain a fine three-dimensional P-wave tomographic model of the crust around the Longmenshan fault zone. The results show that there exist obvious differences between south and north of the Wenchuan mainshock in the seismic structure. North of the Wenchuan mainshock there exist much more heterogeneities, where many aftershocks occurred. These results have significantly improved over the previous results suggesting that the Longmenshan fault zone is only a transition zone between different blocks. The source area of the Wenchuan mainshock is underlain by obvious low velocity anomalies, suggesting that there exist fluids within the Longmenshan fault zone. These fluids may affect the occurrence of the large Wenchuan earthquake. The present results provide significantly seismological evidence for the upward intrusion of the lower crustal flow along the Longmenshan fault zone.
The mechanics of fault slip of MS8.0 Wenchuan earthquake
汶川MS8.0级地震断层滑动机制研究

DU Yi,XIE Fu-Ren,ZHANG Xiao-Liang,JING Zhen-Jie,
杜义

地球物理学报 , 2009,
Abstract: 汶川MS8.0级地震的发震构造为龙门山断裂带,地震地表破裂主要分布在其中的北川-映秀断裂和江油-灌县断裂上,尤其是沿前者发育了长达240 km左右的地表破裂带.通过对龙门山断裂带震后断层擦痕的测量,得到311条断层擦痕数据,利用由断层滑动资料反演构造应力张量的计算方法,得到研究区8个测点的构造应力张量数据,并获得了研究区构造应力场特征:区域现代构造应力场以近水平挤压为主,最大主应力方向(σ1)为76°~121°,平均倾角9°,应力结构以逆断型为主.受构造应力场及断层几何特征的影响,地表破裂呈现出分段性:映秀—北川段主要以NW盘逆冲为主,垂直位移明显;北川以北段为逆冲兼走滑,水平位移量与垂直位移量基本相当,或水平位移略大.
Aftershock distribution of the MS8.0 Wenchuan earthquake and three dimensional P-wave velocity structure in and around source region
汶川MS8.0级地震余震分布及周边区域P波三维速度结构研究

WU Jian-Ping,HUANG Yuan,ZHANG Tian-Zhong,MING Yue-Hong,FANG Li-Hua,
吴建平

地球物理学报 , 2009,
Abstract: 利用川滇地区长期积累的地震走时观测资料和汶川地震余震观测资料对汶川地震震源区及周边区域地壳和上地幔P波三维速度结构进行了研究.结果表明,浅部P波速度分布与地表地质之间具有很好的对应关系.龙门山断裂带在20 km以上深度表现为高速异常带,彭灌杂岩体和宝兴杂岩体为局部高速异常区.龙门山断裂带中上地壳的局部高速异常体对汶川地震的余震分布具有明显的控制作用.在余震带南端,余震全部发生在与宝兴杂岩体对应的高速异常体的东北侧;在余震带的中段,与彭灌杂岩体对应的高速异常体在一定程度上控制了余震的分布;在余震带的东北端,宁强—勉县一带的高速异常体可能阻止了余震进一步向东北扩展.龙门山断裂带中上地壳的P波高速异常表明介质具有相对较高的强度,在青藏高原物质向东挤出过程中起到了较强的阻挡作用,有利于深部能量积累.在30 km深度之下,扬子地块具有明显的高速特征,其前缘随深度增加向青藏高原方向扩展,在下地壳和上地幔顶部已达到龙门山断裂带以西.
Late Quaternary kinematic characteristic of the back range faults at the Middle Longmenshan fault zone
龙门山中段后山断裂带晚第四纪运动特征

TANG Fang-tou,DENG Zhi-hui,LIANG Xiao-hua,JIANG Fu,
唐方头

地球物理学进展 , 2008,
Abstract: The Longmenshan fault zone is a huge multiple thrust fault at the middle on the eastern margin of the Qinghai-Tibet Plateau.It consists of a lot of thrust faults and nappes.It is the boundary between the very active Qinghai-Tibet block and inactive Sichuan block.The latest activity of the fault zone has been attracting much attention of many scientists at home and abroad.The Longmenshan fault zone consists of the back range,the central and the front range faults,which differ from each other in size and activity.Meanwhile,the activity of the whole fault zone is characterized by segmentation.In this study,we made a detailed field investigation on the back range faults at the middle segment of the fault and collected many samples from the strata covering the fault or from fault zone materials for TL and ESR dating.According to the observation of the back range faults at the middle Longmenshan fault zone and dating results,it can be concluded that the back range faults have the tendency to age from the Maowen fault to the Guasiling fault,that is from eastsouthern fault to westnorthern fault.It shows that the back range faults also have an advancing thrust characteristic during late Cenozoic.The main fault,that is the Maowen fault,has been active since late Pleistocene.However,there also is extensional deformation besides thrust deformatiom at the back range faults.This may provide important information for the study of the kinematics and geodynamics of the Qinghai Tibet Plateau.
EXPLORATION OF FAULT ZONE TRAPPED WAVES AT PINGTONG TOWN IN WENCHUAN EARTHQUAKE REGION
汶川地震区平通镇断层围陷波探测

Lai Xiaoling,Li Songlin,
赖晓玲
,李松林

大地测量与地球动力学 , 2008,
Abstract: Pingtong Town locates just over the fractured zone of the Wenchuan Ms8.0 earthquake and the damage at the surface is very serious.The observational line with its middle point at an earthquake exploration trough crosses the fractured zone,and stretches in NW-SE direction,whose total length is about 400 m.The observational results show that the fault zone trapped waves from the fractured zone of Wenchuan Ms 8.0 earthquake were observed.That indicates that there is a great difference in physical property betwe...
Interseismic deformation across the Longmenshan fault zone before the 2008 M8.0 Wenchuan earthquake
2008年汶川8.0级地震前横跨龙门山断裂带的震间形变

DU Fang,WEN Xue-Ze,ZHANG Pei-Zhen,WANG Qing-Liang,
杜方

地球物理学报 , 2009,
Abstract: 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.
The relationship between water contents and deformation of the main minerals in ductile shear zone in Longmenshan
龙门山韧性剪切带主要矿物结构水含量与变形的关系

Jing C,Zhou YS,Lan CY,
靖晨
,周永胜,兰彩云

岩石学报 , 2010,
Abstract: 矿物中的各种水对变形有显著影响。本文研究了龙门山中央断裂带映秀-北川断裂南段韧性剪切带花岗质岩中石英和长石的变形和水含量的关系。通过显微镜下统计石英、长石的粒度和轴比,得出剪切带中花岗质岩石的变形程度分为: 弱变形带和过渡带的花岗片麻岩以及强变形带的初糜棱岩。其中弱变形和过渡变形样品中有细粒化强变形条带。根据石英动态重结晶粒度与流动应力关系,计算了剪切带的流动应力约15~200MPa。利用稳态流变方程,估算出韧性剪切带的变形温度范围400~550℃。花岗质岩石和细粒化剪切带的全岩化学成分分析显示,强变形导致SiO2、K2O减小,Fe2O3、CaO、MgO、LOI增大。Fe、Mg含量增大,K含量降低。显然说明长石含量降低,铁镁质矿物含量增多,初步认为是长石经水解反应发生云母化导致的。利用傅里叶变换红外吸收光谱仪(FTIR)对剪切带花岗质岩石中的主要矿物石英和长石进行了结构水含量的分析,结果表明长石的水含量高于石英的水含量,弱变形的粗粒长石和石英的水含量低于强烈变形的细粒长石和石英的含水量,即随着变形程度的增强,矿物中的含水量呈增加趋势。因此,在剪切带中,强烈剪切变形导致长石和石英晶体位错密度变大,形成点缺陷和缺陷,这些缺陷中被OH充填,形成结构水。这种结构水促进了剪切带中岩石的变形。
DEFORMATION FEATURES OF SURFACE RUPTURE OF THE WENCHUAN EARTHQUAKE(M8.0)AT THE PINGTONG TOWN
汶川8.0地震地表破裂平通镇段的变形特征

He Zhongtai,Ma Baoqi,Tian Qinjian,Zhang Shimin,
何仲太
,马保起,田勤俭,张世民

第四纪研究 , 2008,
Abstract: On May 12,2008,a devastating M8.0 earthquake struck Wenchuan County,Sichuan Province.Its seismogenic structure is long the Longmenshan fault zone.Its surface rupture occurs on the Beichuan-Yingxiu and the Jiangyou-Guanxian faults with lengths of 200km and 70km,respectively.The surface rupture at the Pingtong town is a typical form,including co-seismic scarps and echelon fissures on T1and T2 terraces of the Ping River.We surveyed the rupture surface at the site with GPS RTK technique,especially the middle line of the road and the western wall of the fishpond for estimate the co-seismic displacement.We plotted high resolution DEM and large-scale topographic maps.From the DEM and the topographic map we can infer that the co-seismic vertical and strike-slip displacements are 3.0±0.1m and 4.0±0.2m,respectively.The compressed shortening is about 2.5m derived from calculating the original length of the western deformed fishpond wall.At Pington town,the attitude of the seismogenic fault is NE40°/NW∠50°.The strike-slip displacement at Pingtong town is close to the maximum co-seismic strike-slip displacements created by the earthquake,while the vertical one is smaller than the maximum co-seismic vertical displacement.
Variations of Moho Depth and Velocity Ratio along and surrounding the Longmenshan Fault Zone from Tele-seismic Receiver Functions
用远震接收函数研究龙门山断裂带与其邻区的莫霍面深度及波速比分布

LONG Feng,NI Si-dao,WEN Xue-ze,
龙锋
,倪四道,闻学泽

地球学报 , 2011,
Abstract: 利用龙门山断裂带及其邻近地区地震台站的远震波形记录, 采用时间域迭代反褶积技术求取接收函数, 并用H-Kappa叠加方法计算出各台站下方的莫霍面深度和波速比及其相应的误差。结果除了获得与前人研究大体相同的莫霍面深度分布轮廓外, 还获得一些新的细节与认识: (1)莫霍面深度在四川盆地内为41~48 km, 在四川盆地西缘存在一个NNE向的“舌状”莫霍面隆起带, 对应了龙门山逆冲构造带的前陆拗陷地带。(2)莫霍面深度从龙门山断裂带东缘的约42 km向西很快增加到56 km以上, 形成一个总体展布为NE-NNE向的莫霍面深度的梯度带; 该梯度带在龙门山断裂带北段和中段的走向大体与断裂带平行; 然而, 在龙门山断裂带南段地区, 莫霍面深度梯度带展布转为NNE向, 与断裂带走向呈15°~20°的交角, 且梯度显著增高。(3)龙门山断裂带及青藏高原一侧各台站之下的莫霍面深度误差较大, 可能与那里较复杂的地壳-幔结构、构造有关。(4)波速比的空间差异不明显, 初步认为四川盆地一侧和青藏高原一侧的中-高波速比异常可能分别与台站下方存在含水沉积层以及壳内低速层(或通道流)有关。
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