Current tectonic deformation and seismogenic characteristics along the northeast margin of Qinghai -Xizang block

Introduction The northeast margin of Qinghai-Xizang block has become the place with close attentions from geo-specialists at home and abroad for its significant tectonic movement and intensive seismicity. Quite a number of achievements have been obtained from the studies on geological structures and strong earthquake activities (DING, LU, 1989, 1991; GUO, et al, 1992, 2000; GUO, XIANG, 1993; HOU, et al, 1999; Tapponnier, et al, 1990; Gaudemer, et al, 1995). In the Development Program…     

Source process of the 1990 Gonghe,China, earthquake and tectonic stress field in the northeastern Qinghai-Xizang (Tibetan) plateau

TheM _s =6.9 Gonghe, China, earthquake of April 26, 1990 is the largest earthquake to have been documented historically as well as recorded instrumentally in the northeastern Qinghai-Xizang (Tibetan) plateau. The source process of this earthquake and the tectonic stress field in the northeastern Qinghai-Xizang plateau are investigated using geodetic and seismic data. The leveling data are used to invert the focal mechanism, the shape of the slipped region and the slip distribution on the fault plane. It is obtained through inversion of the leveling data that this earthquake was caused by a mainly reverse dip-slipping buried fault with strike 102°, dip 46° to SSW, rake 86° and a seismic moment of 9,4×10¹⁸ Nm. The stress drop, strain and energy released for this earthquake are estimated to be 4.9 MPa, 7.4×10^–5 and 7.0×10¹⁴ J, respectively. The slip distributes in a region slightly deep from NWW to SEE, with two nuclei, i.e., knots with highly concentrated slip, located in a shallower depth in the NWW and a deeper depth in the SEE, respectively.Broadband body waves data recorded by the China Digital Seismograph Network (CDSN) for the Gonghe earthquake are used to retrieve the source process of the earthquakes. It is found through moment-tensor inversion that theM _s =6.9 main shock is a complex rupture process dominated by shear faulting with scalar seismic moment of the best double-couple of 9.4×10¹⁸ Nm, which is identical to the seismic moment determined from leveling data. The moment rate tensor functions reveal that this earthquake consists of three consecutive events. The first event, with a scalar seismic moment of 4.7×10¹⁸ Nm, occurred between 0–12 s, and has a focal mechanism similar to that inverted from leveling data. The second event, with a smaller seismic moment of 2.1×10¹⁸ Nm, occurred between 12–31 s, and has a variable focal mechanism. The third event, with a sealar seismic moment of 2.5×10¹⁸ Nm, occurred between 31–41 s, and has a focal mechanism similar to that inverted from leveling data. The strike of the 1990 Gonghe earthquake, and the significantly reverse dip-slip with minor left-lateral strike-slip motion suggest that the pressure axis of the tectonic stress field in the northeastern Qinghai-Xizang plateau is close to horizontal and oriented NNE to SSW, consistent with the relative collision motion between the Indian and Eurasian plates. The predominant thrust mechanism and the complexity in the tempo-spatial rupture process of the Gonghe earthquake, as revealed by the geodetic and seismic data, is generally consistent with the overall distribution of isoseismals, aftershock seismicity and the geometry of intersecting faults structure in the Gonghe basin of the northeastern Qinghai-Xizang plateau.Contribution No. 96 B0006 Institute of Geophysics, State Seismological Bureau, Beijing, China.     

Present-day tectonic movement in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau as revealed by earthquake activity

IntroductionAccording to the division of Neo-tectonically active blocks northeastern Qinghai-Xizang (abbreviated as QX thereafter) plateau is a juncture region where 3 intra-continental subplates, the Qinghai-Xizang, Xinjiang and North China subplate, meet with each other (DING, 1991). The subplates generally consist of blocks. Specifically, around the Yinchuan-Haiyuan (quasi-trijuncture( (TIAN, DING, 1998), where the 3 subplates meet, to the south locates the Gansu-Qinghai (GQ) blo…     

Present-day tectonic movement in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau as revealed by earthquake activity

Characteristics of present-day tectonic movement in the northeastern margin of Qinghai-Xizang plateau (Tibetan) are studied based on earthquake data. Evidence of earthquake activity shows that junctures between blocks in this area consist of complicated deformation zones. Between the Gansu-Qinghai block and Alxa block there is a broad compressive deformation zone, which turns essentially to be a network-like deformation region to the southeast. The Liupanshan region, where the Gansu-Qinghai block contacts the Ordos block, is suffering from NE-SW compressive deformation. Junction zone between the Ordos and Alxa block is a shear zone with sections of variable trend. The northwestern and southeastern marginal region of the Ordos is under NNW-SSE extension. The above characteristics of present-day tectonic deformation of the northeastern Qinghai-Xizang plateau may be attributed to the northeastward squeezing of the plateau and the resistance of the Ordos block, as well as the southeastward extrusion of the plateau materials. Foundation item: State Natural Science Foundation of China (49732090) and the Development Program on National Key Basic Researches under the Project Mechanism and Prediction of Continental Strong Earthquakes (95-13-02-05). Contribution No. 00FE2003, Institute of Geophysics, China Seismological Bureau.     

Relocation of earthquakes in northeastern region of Qinghai-Xizang plateau and characteristics of earthquake activity

IntroductionThenortheasternregionofQinghai-Xizangplateauisthejunctionregionofthethreeblocks,ie.,Qinghai-Xizang,AIxaandordosblock.TianandDing(l998)studiedtheclockwisetypequasi-trijunctionaroundHaiyuan-YinchuaninnortheasternregionofQinghai-Xizangplateau.Thethreet6ctonicbranchesofthequasi4rjunctionareQiIianshanfaultzone,Yinchuan-Jedai-Linhe(YJL)fractureddepressionbasinandLiupanshanfaultzone.TheQilianshanfaultzoneshowssin-istraIandcompressionalmovement,themovementofYJLbasinisofdextraland…     

青藏高原岩石圈多层构造应力场

青藏高原构造应力场可按岩石圈下层、多震层和浅层地壳区分为三层。除了震源机制解方法和井孔原地测量方法可分别用于推测多震层和浅层的应力状况外,还可根据下层塑性流动网络,采用平分网络共轭角的方法估计下层的应力方向。对比岩石圈下层与上层(多震层)的构造应力场,其结果表明: 由于板块边缘驱动力主要通过下层的网络状流动实现其远程传递,故在总体作用趋势上,上层的应力方向受控于下层;又由于高原靠近喜马拉雅驱动边界,部分驱动力直接沿上层传递,致使局部地区上、下层应力方向相差显著。     

青藏高原东北缘构造应力场及动力学特征

青藏高原东北缘是高原物质挤出的重要通道,也是深入认识青藏高原构造隆升和横向扩展机制的重要区域.本文利用中国地震台网在青藏高原东北缘布设的宽频带地震仪记录的波形资料,利用CAP全波形反演方法及基于P波初动极性和S/P振幅比的HASH方法,获得了研究区内M_L≥3.0地震震源机制解781组,同时收集了M_W≥4.6中强地震震源机制解96组,利用STASI阻尼区域应力场反演算法对该区的构造应力场分布特征进行了分析.结果显示,研究区震源机制P轴、T轴以及最大主应力轴σ₁和最小主应力轴σ₃总体上倾伏角较小,揭示了近水平的挤压或剪切应力环境.σ₁以NE向为主,且由巴颜喀拉块体西南部向外呈扇形辐射,至祁连造山带逆时针偏转为NNE向,至秦岭造山带顺时针偏转为ENE向—ESE向,分布特征与区内走滑型边界断裂活动性质相对应.水平最大主应力S_Hmax方向与σ₁分布特征基本一致,应力结构类型以走滑型为主,且R值具有明显的空间差异分布特征.柴达木—陇西块体和巴颜喀拉块体东南部与秦岭造山带和四川盆地的过渡区域,深浅地壳S_Hmax方向具有差异性,深部地壳变形与浅部可能发生解耦,其余区域不同地壳深度的S_Hmax方向一致性较好.联合基于原位地应力实测获得的地壳浅表层地应力状态、基于地震各向异性获得的地壳和上地幔变形特征以及基于GPS观测获得的地壳浅表层形变特征,讨论了青藏高原东北缘岩石圈垂向变形特征及动力学机制.结果表明青藏高原东北缘应力场与应变场特征一致,地表形变主要受控于区域构造应力场.壳幔变形机制和深部动力学特征极为复杂,很难用单一模式解释,青藏高原东北缘可能以岩石圈连续增厚变形与下地壳通道流的共同作用模式为主.

     

青藏高原及周缘地壳浅层构造应力场量值特征分析

以"中国大陆地壳应力环境基础数据库"中的实测地应力数据为基础,合理筛选出地理空间范围为21°N—40°N,73°N —110°N的近2000条数据,深度范围0~2 km.通过将研究区内实测地应力扣除重力影响,并考虑数据样本数量沿深度分布不均匀的问题,分析构造应力场的作用.重力影响的扣除采用海姆假说与金尼克假说两种模式估算其下限与上限,给出了青藏高原及周缘及青藏地块、南北地震带北、中、南段上构造应力和构造差应力随深度分布的特征和量值范围.结果显示：（1）青藏高原及周缘地区最大水平应力σH、最小水平应力σh随深度D呈线性增加：σH=22.115D+5.761、σh= 14.893D+3.269;最大水平构造应力σT、最小水平构造应力σt的量值估算范围分别为4.609 < σT < 15.522D+4.609、3.121 < σt < 6.366D+3.121（D >0）;构造差应力σT-σt=7.222D+2.492,地表值（D=0 km）为2.5 MPa左右,随深度增加以7.2 MPa·km-1的梯度增大;（2）在测量深度范围内,青藏地块、南北地震带北、中、南段研究区σT、σt、σT-σt随埋深均呈线性增大;D=1 km时,各地块σT的统计回归值中最大为30.1 MPa,最小为17.6 MPa,量值由大到小排序依次为：青藏地块、南北带北段、南北带中段、南北带南段;D=1 km时,各地块σT-σt的统计回归值中最大为15.8 MPa,最小为8.9 MPa,量值由大到小排序依次为：青藏地块、南北带北段、南北带中段和南北带南段.总体表现为青藏地块强、南北带较弱的基本特征.（3）与南北带相比较,青藏地块地壳在从南向北的挤压作用下呈现出明显的"浅弱深强"特点.     

Basic characteristics of recent tectonic stress field in southwest China

Direction and structure characteristics of 58 tectonic stress tensors have been determined in 41 surveyed areas (points) in the southwestern district of China through a calculation method for inversion of tectonic stress tensors from sliding direction of faults, and, in combination with seismic mechanism solution andin-situ stress measurements, the following characteristics of the recent tectonic stress fields in the southwestern district of China have been defined: (1) the stress fields in this district have remained stable since the end of early to mid-Pleistocene; (2) the effect of such tectonic stresses is mainly horizontal; (3) the orientation of the maximum principal stress axis shows a trend of regular rotation from north to south, i. e. from NEE-SWW in northern Songpan and Longmen Shan areas to sub-EW in the central part of western Sichuan, and further to NNW-SWW or sub-SN in Yunnan; (4) the regional tectonic stress fields are of distinct division character; (5) there is well concordance between the main direction and type of stress structures in the stress tate both in deep and shallow parts of the crust. In addition, studies of staged tectonic stress tensors preliminarily show that in early Quaternary the southwestern district was mainly affected by lateral compression of Indian plate, under which the regional tectonic stress fields mainly display NE-sub-EW compression. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 407–417, 1993.     

区域构造应力场的某些变化特征

应用现代中小地震的震源机制解 ,以山东地区为例 ,推断了该区的现今构造应力场 ,分析了区域构造应力场整体与局部变化特点。在此基础上 ,探讨了区域构造应力场与地震活动的关系     

Evolution of 3D tectonic stress field and fault movement in North China

IntroductionThe research on stress field interior the Earth is an either relative old or young branch of geoscience. Early in the 20th century, in order to learn the state of inner stress field, a few scholars had used simple ideal model to analyze big scale tectonic conformations and activities according to tide, gravity, rotation and inner thermal materials. So far, lots of problems on the state of the Earth stress field have not been solved completely yet. The origin of stress field, the d…     

The Tectonic Feature of a Quasi-Trij unction in the Northeastern Corner of Qinghai-Xizang Plateau

Quasi-trijunction is a type of popular structure for certain scale tectonic blocks in a continent. There are two kinds of quasi-trijunction in the conjoining area formed due to rotation of continental blocks. They are the clockwise type and the anticlockwise type of quasi-trij unction. The shape of a quasi-trij unction may be gradually changed associated with block rotation and tectonic evolution, but, sediments and structure in the conjoining area can record the history of tectonic evolution. Thus, studying a quasi-trij unction can reveal regional tectonic evolution.Regional tectonic movement, plane strain partitioning and characteristics of seismic activity can be studied based on kinematics and geometric analysis of a quasi-trijunction.The quasi-trijunction is a surface structure controlled by deep crustal movement. Tectonic activity may be different in three branches. In the quasi-trijunction in the northeastern corner of Qinghai-Xizang Plateau, the NWW-trending Qilianshan-Hexi corridor fault zone w     

兰州至玛曲地区地应力测量与现今构造应力场特征研究

兰州—玛曲地区是印度板块北东向推挤引起青藏块体强烈变形的前缘区,该区的现今构造应力场研究对研究大陆动力学问题具有重要意义.本文给出了兰州—玛曲地区不同地点的现今地应力实测值的大小和方向.测量方法采用压磁应力解除法,测点分别布置在阿姨山、大水、尕海、玛艾以及清水.为系统研究本区及邻近地区现今构造应力场特征,对已有应力实测数据进行了整理分析.研究结果表明,本区及邻区几十米浅表部应力与其他地区相比,属于中等大小量值;应力随深度增加而加大,但在不同构造单元,应力增加梯度有所不同;最大水平主应力方向总体上为北东向,不同构造单元上方向有所不同,鄂尔多斯地块最大水平主应力方向为近东西向,河西走廊带最大水平主应力方向在北北西—北东方向内变化,祁连山东南端最大水平主应力方向变化较大,西秦岭地块是现今地应力的一个过渡带,最大水平主应力方向由北侧的NE向逐渐转变为中部的EW向和南侧的SEE向.本文给出的结果与由GPS观测给出的该区域应变场分布具有一致性.     

Focal mechanisms and tectonic stress field of the Xinfengjiang earthquake

Altogether 83 events were recorded clearly by all the 8 sub-seismometric stations of the telemetrered seismic network in the Xinfengjiang area during the period from October 1st 1983 to April 30th 1987. Based upon the difference of the initial motion of P waves, the authors divided the 83 earthquakes into 37 pattens. Combining similar pattens, we have got 5 types of focal mechanism solutions. The recent tectonic stress field of the Xinfengjiang region is discussed. The characteristics of the stress axis and the nodal planes are different from which our predecessors got earlier; but the present results is similar to which put forward by the authors in 1981. This paper shows that the tectonic stress field is clearly characterized by a compression in the N-S direction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica 13. 462–476, 1991.     

中国大陆地壳应力场与构造运动区域特征研究

系统研究了1918～2006年间中国大陆及其周缘发生的3115个M4.6以上中、强地震的震源机制解,得到中国大陆地壳区域应力场的压应力轴和张应力轴空间分布的统计结果.探讨了大陆应力场的结构,以及周围板块运动对中国大陆应力场影响作用范围及其界线.结果表明,中国东部的华北地区受到太平洋板块向欧亚板块俯冲挤压的同时,又受到从贝加尔湖经过大华北直至琉球海沟的广阔范围内存在的方位为170°引张应力场的控制.华北地区大地震的震源机制解反映出,该区地震发生为NEE向挤压应力和NNW向张应力的共同作用结果.印度洋板块向欧亚板块的碰撞挤压运动所产生的强烈的挤压应力,控制了喜马拉雅、青藏高原、乃至延伸到天山及其以北的广大地区.在青藏高原周缘地区和中国西部的大范围内,压应力P轴水平分量位于20°~40°,形成了近北东方向的挤压应力场,大量逆断层型强震集中发生在青藏高原的南、北和西部周缘地区以及天山等地区. 本文结果表明,正断层型地震集中发生在青藏高原中部高海拔的地区.证明了青藏高原周缘区域发生南北向强烈挤压短缩的同时,中部高海拔地区存在着明显的近东西向的扩张运动.根据本文最新结果,得到了华北、华南块体之间地壳区域应力场的控制边界线,发现该分界线与大地构造、岩石圈板块构造图等有较大差异,特别是在大别及其以东地区, 该分界线向东南偏转,在沿海的温州附近转向东,最终穿过东海直至琉球海沟.台湾纵谷断层是菲律宾海板块与欧亚板块之间碰撞挤压边界,来自北西西向运动的菲律宾海板块构造应力控制了从台湾纵谷、华南块体,直到中国南北地震带南段东部地域的应力场. 地震震源机制结果还表明,南北地震带南段西侧其P轴大约为NNE方向,与青藏高原的P轴方位一致.南北地震带南段东侧其P轴大约为NWW方向,与华南块体的P轴方位一致.因此,将中〖JP2〗国大陆分成东、西两部分的南北地震带南段是印度洋板块与菲律宾海板块在中国大陆内部影响控制范围的分界线.     

The characteristics of tectonic stress field about strike slip earthquake－generating structure in the Chinese mainland

（环文林，汪素云，宋昭仪）Ｔｈｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｔｅｃｔｏｎｉｃｓｔｒｅｓｓｆｉｅｌｄａｂｏｕｔｓｔｒｉｋｅｓｌｉｐｅａｒｔｈｑｕａｋｅ－ｇｅｎｅｒａｔｉｎｇｓｔｒｕｃｔｕｒｅｉｎｔｈｅＣｈｉｎｅｓｅｍａｉｎｌａｎｄ￥Ｗｅｎ－Ｌｉｎ...     

中国大陆现代构造应力场与强震活动

依据应力性状和力源特征,中国大陆现代构造应力场可划分为四级应力区.它们分别是2个一级应力区、4个二级应力区、5个三级应力区和26个四级应力区.通过分析中国大陆现代构造应力分区与强震活动之问的关系,初步获得以下结论:①构造应力作用强烈和复杂的地区是强震频发的地区;②应力区边界是强震集中发生的地带;③应力方向、应力结构类型...     

南北地震带震源机制解与构造应力场特征

南北地震带作为中国大陆地应力场一级分区的边界,其构造应力场的研究对理解大陆强震机理、构造变形和地震应力的相互作用具有重要意义.本文收集南北地震带1970—2014年的震源机制解819条,按照全球应力图的分类标准对震源机制解进行分类,发现其空间分布特征与地质构造活动性质比较吻合.P轴水平投影指示了活动块体的运动方向,T轴水平投影在川滇块体及邻近地区空间差异特征最为突出,存在顺时针旋转的趋势.南北地震带的最大水平主应力方向具有明显的分区特征,北段为NE向走滑类型的应力状态,中段为NEE—EW—NWW向的逆冲类型,南段为SE—SSE—NS—NNE向走滑和正断类型,在川滇块体的北部和西边界应力状态为EW—SE—SSE的正断层类型,表明来自印度板块的NNE或NE向的水平挤压应力和青藏高原物质东向滑移沿大型走滑断裂带向SE向平移的复合作用控制了南北地震带的岩石圈应力场.川滇块体西边界正断层类型应力状态范围与高分辨率地震学观测得到的中下地壳低速带范围基本吻合,青藏高原向东扩张的塑性物质流与横向边界(丽江—小金河断裂带)的弱化易于应变能的释放,在局部地区使NS向拉张的正断层向EW向拉张正断层转变.反演得到的应力状态基本上与各种类型地震的破裂方式比较吻合,也进一步验证反演结果的可靠性,可为地球动力学过程的模拟和活动断层滑动性质的厘定提供参考.     

Recent tectonic stress field research in Shanxi graben system

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