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.     

2008年新疆乌恰6.8级地震序列震源特征及帕米尔东北缘应力场研究

本文使用新疆区域数字地震台站记录的宽频带长周期数字波形资料,在时间域反演了2008年10月5日新疆乌恰6.8级地震的强余震及其周围先后发生的52次中等强度地震的矩张量解,结合Harvard大学在该区域的地震矩张量结果,研究了帕米尔东北缘的应力场分区特征.研究结果显示,位于印度板块向欧亚板块推挤的前缘及向北凸出的弧型构造的最北缘的卡兹克阿尔特弧形活动褶皱-逆断裂带,以逆冲推覆活动为主,并有部分走滑类型的地震,基本不存在正断层类型的地震;该弧型构造近东西走向的顶部(文中的西区)与其北西走向的东侧(文中的东区)的局部应力场最大主压应力方向不同,分别为NW、NNE方向,显示出在承受印度板块向欧亚板块俯冲作用的同时,东区也更多的受到了塔里木块体顺时针旋转作用的影响.位于帕米尔陆内俯冲和变形作用强烈、碰撞造成深源地震带东段的南区,地震以走滑错动为主, 逆断、正断层都有,显示出相对复杂的应力状态.位于帕米尔高原内部的西区和南区的应力场最大主压应力方向一致,由北向南,由最大主压应力轴接近水平,过渡为最大主张应力轴接近水平,一定程度揭示了板块俯冲的状态.结合南区和西区的地震深度差异及机制解中断层面的倾角,推测在中帕米尔的东部,由北向南的板块俯冲至150~170km深度,俯冲角度为60°左右.     

2016年阿克陶MS 6.7地震地表破裂特征和帕米尔现代构造应力场初步分析

帕米尔高原位于地中海－喜马拉雅地震带上,晚新生代以来随着印度板块向欧亚板块持续不断地挤压汇聚,其构造运动是欧亚大陆最强烈的地区。高原腹地发育一系列近SN向正断层,包括近SN向的塔什库尔干正断层所处的帕米尔中部现代区域的构造应力场以EW向水平拉张为主。2016年11月25日发生的阿克陶M_S 6.7级地震的发震构造为塔什库尔干断层分支的NWW向木吉盆地北缘断层,其具有右旋走滑兼正断性质。地震在震中附近产生同震地表形变带,全长约1km,呈近SN－NNE向水平拉伸,发育近EW—NWW向的张裂缝,为地震破裂的产物,张裂缝的最大水平拉伸位移量和最大垂直位移量分别为46cm和16cm。地表破裂带中的NE和NW向张剪裂缝只是连接贯通这些雁列的张裂缝,其水平相对位移量取决于张裂缝的水平拉伸量和张裂缝之间的几何关系。地表形变带表现的拉张性质与帕米尔高原腹地区域现代应力场最大主压应力为垂直向基本一致,可能与深部热物质上涌造成的上地壳拉伸有关。而地表形变带呈近SN向水平拉张,与区域近EW向拉张应力场之间存在显著差异,这可能是木吉盆地北缘右旋走滑正断层阶区局部应力场调整的结果。     

帕米尔-兴都库什地区的板块俯冲特征

本文利用美国国家地震信息中心（NEIC）提供的1973～2006年地震目录,哈佛大学提供的1978-2005年地震机制解资料,研究了帕米尔-兴都库什地区印度板块与欧亚板块的碰撞形态,分析了印度板块向北俯冲对地震活动及其区域应力场的影响。地震震源三维图象显示：欧亚板块与印度板块在帕米尔＂结＂附近碰撞强烈,地震活动明显增强,震源剖面显示＂V＂字型分布形态;在帕米尔＂结＂东侧,随着印度板块俯冲动力减弱,地震活动也明显减弱,印度板块向北俯冲的剖面形态逐渐消失,欧亚板块向东南俯冲的剖面形态越加清晰;印度板块向北俯冲具有由浅向深、由南向北反复迁移的特征,可能反映印度板块向北俯冲→断离、再俯冲→再断离的过程。由于印度板块与欧亚板块间的强烈碰撞挤压作用,帕米尔-兴都库什地区处于以近南北向的挤压构造应力状态,逆断层数量约占70%,正断层数量约占11%,走滑断层数量约占19%。P轴优势方位显示帕米尔-兴都库什地区主压应力近南北向,倾角近水平,呈现由南向北倾斜;T轴倾角较大,近垂直,整体接近俯冲带的倾向。帕米尔-兴都库什地区应力场特征表明,印度板块向北的主动推挤,是形成这一区域应力场的主动力,向南倾的欧亚板块处于一种被动的被挤压状态。     

Spatiotemporal distribution of seismic activity in East Asia and its relation to regional stress field

Tectonic forces from the relative movements between plates are transmitted into the continental crust, and then they create the earthquake generating stress field there. The space-time distribution of the seismic activity including the small earthquakes in a region reflects the variation of the stress field in the region. According to this idea, the characteristics of the stress fields in the various regions of East Asia have been analyzed in detail in this paper based on a lot of solutions of focal mechanisms and data of seismic activity during the last 500 years. The results indicate that the tectonic forces from the subduction of the Pacific Ocean plate underneath the Eurasian plate control the stress field in the region from North China to the northern part of the North-South Seismic Belt. The variation of the regional stress field shown by the variation of seismic activity in some regions of Japan has also been discussed based on characteristics of variation of the seimicity of small earthquakes. Synchronous variations of seismicity in the past 100 years or so in West China and in the boundary region between the Indo-Australian and Eurasian plates implicate that there is the transmission of tectonic forces into West China through the collision between the Indo-Australian and Eurasian plates. The active seismic activity in the boundary region between the Indo-Australian and the Eurasian plates and in West China is continuing consistently. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 287–294, 1991.     

东亚地震活动的时空分布及其与区域应力场的关系

来自板块之间相对运动的构造力可以传递到大陆地壳,从而形成了大陆内部的地震应力场.在某一地区,包括小地震在内的地震活动性的分布可以反映该地区的应力场的变化.根据这一观点,本文根据大量的震源机制解的结果以及最近500年的地震活动资料,详细地研究了东亚地区内几个地区的区域应力场的特征.其结果表明,来自太平洋板块相对欧亚板块的俯冲所形成的构造力,控制了从华北地区到南北地震带北段的应力场.本文根据小震的地震活动变化的特征,讨论了日本一部分地区由地震活动性的变化所反映的区域应力场的变化.中国西部以及印度-澳大利亚和欧亚大陆板块边界地区,最近大约100年地震活动性的同步变化表明,来自印度-澳大利亚板块和欧亚板块碰撞所产生的构造力,传递到了中国西部.印度-澳大利亚板块和欧亚大陆板块边界,以及中国西部的地震活动,现在依然处在地震活动高潮期.      

Is there an active subduction beneath the Gibraltar orogenic arc? Constraints from Pliocene to present-day stress field

We present a new set of brittle microtectonic measurements carried out in the Pliocene and Quaternary rocks outcropping in several key sectors of the western Betic and Rif orogen, the so-called Gibraltar orogenic arc. This data set, along with available earthquake focal mechanisms and borehole breakouts, allowed us to compile the Pliocene and Quaternary stress map of this area. This map provides new constraints for tectonic models and the present-day tectonic activity of the proposed active eastward subduction of oceanic lithosphere beneath the Gibraltar Arc and roll-back. The horizontal maximum compressive stress (S_Hmax) is NW-SE in the Betic Orogen and N-S/NNW-SSE in the southern Rif Cordillera. There is a significant consistency between S_Hmax and the displacement field deduced from GPS measurements with respect to the African plate: both appear to reflect the NW-SE convergence between the African and the European plates that is perturbed in the Rif. We propose that part of the eastern Rif behaves as a quasi-rigid block welded to the stable African plate. This block is bounded by important faults that localized most of the deformation disturbing the stress and surface displacement field. Pliocene to Quaternary N-S to NW-SE Africa-Europe plate convergence seem to be associated to the reorganization of the remnant Early Miocene subduction system in a continental–continental collision framework. Three-dimensional reconstruction of available seismic tomography plotted against the intermediate seismicity shows that only part of the old subduction system, whose orientation ranges from N20°E to N100°E, remains active: the portion ranging from N30°E to N40°E, orthogonal to the regional convergence.     

藏东南及周边地区地震活动特征研究

藏东南及周边地区是印度板块与欧亚板块动力碰撞的影响区, 该区历史地震活动强烈, 曾发生过1950年墨脱—察隅8.6级和1951年当雄8.0级地震。 本文首先介绍藏东南及周边地区的地质构造背景, 其次通过考察该地区强震活动情况和活动地块边界带相关段落的加卸载响应比(LURR)时序特征, 分析了研究区的强震活动状态。 从历史地震活动看, 安达曼弧地区与喜马拉雅东构造结地区强震活动存在一定的动力关联, 当前研究区域的周边动力环境表现为安达曼弧地区地震活动强烈和东构造结地区的持续平静。 从地震活动图像看, 1980年以来6级以上地震在藏东南及周边地区已经形成空区, 表现类似于1950年墨脱—察隅地震前的空间分布特征。 从活动地块边界带相关段落LURR时序特征看, 喜马拉雅带东段现处于高应力状态, 其次为澜沧江带与三江带。     

南黄海和东海地区现代构造应力场特征的研究

分析研究了南黄海和东海地区18口石油勘探钻井的井孔崩落特征，结合对琉球岛弧和冲绳海槽地区浅源地震震源机制解的分析，确认了南黄海地区与我国华北地区有类似的现代构造应力场特征；并得出东海地区的最大水平压应力方向为NEE-SWW，最小水平压应力方向为NNW-SSE，它们分别与冲绳海槽地区的最大和最小主压应力方向接近;东海地区地壳上层的水平差应力可能不强，这与该地区没什么地震活动的特点是一致的．根据应力场特征推断，我国东部地区并未受到菲律宾海板块俯冲的推挤作用，而是可能受到垂直于冲绳海槽走向的拉伸作用的影响．     

琉球岛弧地区的地震分布、Benioff带形态及应力状态h

利用ISC及中国台网的资料,研究了琉球岛弧及冲绳海槽的地震分布及震源机制解,讨论了Benioff带的形态及应力状态.mb4.0的地震主要分布于琉球海沟西侧的弧形带,并形成明显的Benioff带.吐噶喇海峡以北俯冲带弯曲明显,深部倾角大,约92,70km以下张应力轴沿俯冲方向;吐噶喇海峡以南,俯冲带较平直,深部倾角较小,约55,压应力轴基本沿俯冲方向。冲绳海槽内处于NNW向近水平的拉伸,华北应力场与之类似,没有受到菲律宾海块挤压作用的影响.      

中国大陆及邻区板内应力场的数值模拟及动力机制探讨

中国大陆位于欧亚板块的东南部, 受到印度板块、太平洋板块和菲律宾海板块的碰撞挤压与俯冲作用, 其构造应力场形态和动力学机制相当复杂. 本文采用伪三维有限元方法, 以世界应力图2008年版本数据(WSM2008)的应力方向和应力型两类指标作为主要约束, 对中国大陆及邻区的动力驱动机制进行数值模拟, 给出了中国大陆周边地区板块边界力的大小和方向估计. 同时对3个典型情况的数值模型进行了分析. 结果显示, 软流层静压推力对该区域构造应力场影响相对较小, 板块边界力作用则起主导作用; 印度板块在喜马拉雅造山带对欧亚板块的碰撞控制了中国大陆地区应力场的基本形态, 是形成川滇地区走滑型地震为主的重要原因; 琉球海沟——南海海槽俯冲带边界力显示了挤压-张性的分段特性, 贝加尔裂谷表现为拉张作用. 进一步的分析表明, 中国大陆大部分区域内最大水平剪应力分布图像与该地区地震辐射能量密度的分布存在较好的空间正相关性．      

中国西部及邻区活动地块边界带现代构造应力场

利用哈佛全球矩心矩张量解数据和许忠淮认为1920mdash;1999年可靠的中国大陆震源机制解数据, 反演了中国西部及邻区活动地块边界带上现代构造应力场．通过对FMSI反演程序多次的输入和检验, 得到了边界带上的应力场．边界带上最大主压应力sigma;1轴绝大多数近水平. 在90deg;E以西的中国西部大陆及邻区, sigma;1轴水平方向基本上为近SN向;在青藏高原的东北部, sigma;1轴水平方向基本上为近NE向;在青藏高原的东南部, sigma;1轴水平方向绕喜马拉雅构造东端顺时针方向旋转．最小主压应力sigma;3轴倾角呈两极分布,西域地块区内活动地块边界带和青藏地块区内东北缘部分段sigma;3轴倾角较陡, 而青藏地块区内sigma;3轴倾角近水平, 所以西域地块区和青藏地块区内东北部相对于其它大部分青藏地块区, 有更多的逆冲地震．应力场在同一个边界带具有非均匀性. 北天山带、南天山带、西秦岭mdash;德令哈带、岷山mdash;龙门山带和安宁河mdash;小江带的非均匀性相对要小一些, 西昆仑带、海原mdash;祁连带、东昆仑带、玛尼mdash;玉树带、澜沧江带和滇西西边界带的非均匀性相对要大, 而喀喇昆仑mdash;嘉黎带和喜马拉雅带的非均匀性最显著．由于震源机制解数据的限制, 本文给出的是边界带上部分段的应力场．      

东亚大陆、 西亚大陆和东地中海地区地震活动性异同的初步综述

本文初步综述了东亚大陆、 西亚大陆和东地中海地震区地震活动性异同。 地震活动性的含义不仅指地震的时空强图像, 也包括地震的构造和动力学背景分析。 结果表明, 总体上东亚大陆、 西亚大陆和东地中海地区的地震活动性和变形, 都和欧亚板块与周边(北美、 太平洋、 菲律宾海、 印度、 阿拉伯和非洲等)板块等相互作用(汇聚、 碰撞、 俯冲和速度)密切相关。 宏观上, 东亚大陆、 西亚大陆和东地中海地区的地震活动性都表现为疏密相间的震中分布图像以及断裂走向的对称性等。 然而, 在这些大陆地震区相关的板块相互作用的边界上以及内部的地震活动、 构造和动力学背景等方面仍存在不少差异。     

横跨喜马拉雅造山带的构造运动转换与变形分配

喜马拉雅造山带包含喜马拉雅弧和东、西构造结3个基本部分,它们是大陆碰撞后印度板块继续向北移动,并向西藏高原下俯冲产生的构造变形系统.该系统的重要地质特征之一,是同时存在多种不同样式、不同或相反性质的地壳变形,例如地壳南北向缩短与东西向伸展,高原隆起与山间盆地下沉,与造山带走向大致平行的向北倾斜或向南倾斜的逆断层,东西向...     

Alpine tectonic evolution of a Jurassic subduction-accretionary complex: Deformation,kinematics and Ar/Ar age constraints on the Mesozoic low-grade schists of the Circum-Rhodope Belt in the eastern Rhodope-Thrace region,Bulgaria-Greece

Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc–Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D₁ is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D₂. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1–39.7 Ma ⁴⁰Ar/³⁹Ar mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane.     

Moment Tensor Solutions of Earthquakes in the Indian Ocean from Surface Waves and their Tectonic Implications

—Rayleigh and Love waves generated by sixteen earthquakes which occurred in the Indian Ocean and were recorded at 13 WWSSN stations of Asia, Africa and Australia are used to determine the moment tensor solution of these earthquakes. A combination of thrust and strike-slip faulting is obtained for earthquakes occurring in the Bay of Bengal. Thrust, strike slip or normal faulting (or either of the combination) is obtained for earthquakes occurring in the Arabian Sea and the Indian Ocean. The resultant compressive and tensional stress directions are estimated from more than 300 centroid moment tensor (CMT) solution of earthquakes occurring in different parts of the Indian Ocean. The resultant compressive stress directions are changing from north-south to east-west and the resultant tensional stress directions from east-west to north-south in different parts of the Indian Ocean. The results infer the counterclockwise movement of the region (0°–33°S and 64°E–94°E), stretching from the Rodriguez triple junction to the intense deformation zone of the central Indian Ocean and the formation of a new subduction zone (island arc) beneath the intense deformation zone of the central Indian Ocean and another at the southern part of the central Indian basin. The compressive stress direction is along the ridge axis and the extensional stress manifests across the ridge axis. The north-south to northeast-south west compression and east-west to northwest-southeast extension in the Indian Ocean suggest the northward underthrusting of the Indian plate beneath the Eurasian plate and the subduction beneath the Sunda arc region in the eastern part. The focal depth of earthquakes is estimated to be shallow, varying from 4 to 20 km and increasing gradually in the age of the oceanic lithosphere with the focal depth of earthquakes in the Indian Ocean.     

汤加—克马德克俯冲带现今非均匀应力场特征及其动力学意义

汤加—克马德克俯冲带是太平洋板块向澳大利亚板块俯冲碰撞的动力作用区,是全球俯冲带动力学研究的热点区域.本研究基于EHB地震目录,对汤加—克马德克俯冲带(18.5°S—28.5°S)区域进行平面拟合,得到该范围内俯冲带走向约为196°,倾角约为48°;利用该俯冲带研究区域内Global CMT目录,对不同位置、不同深度进行区域应力张量反演,得到汤加—克马德克俯冲带研究区内精细的应力图像.结果显示:(1)俯冲带浅部(60~300km)应力结构非均匀特征明显,主应力轴倾伏角变化多样,并且最大主压应力轴方位在24°S左右发生明显偏转,我们推测这可能与洋底构造路易斯维尔海链俯冲有关;(2)中部(300~500km)最大主压、主张应力轴由北向南逐渐发生偏转,这可能与由北向南流动的地幔流对俯冲板片产生推挤作用有关,并且这种推挤作用向南逐渐减弱;(3)深部(500~700km)最大主压应力轴沿俯冲方向分布;(4)本文的结果还发现了主俯冲带深部西侧"偏移"板片与主俯冲带应力结构不同,表明"偏移"板片与主俯冲带是分离的.     

Volcanoes of the southwestern extension of the active Mariana island arc: New swath-mapping and geochemical studies

Until recently it was thought that the volcanoes of the Mariana island arc of the western Pacific terminated at Tracey Seamount at ∼ 14°N immediately west of Guam. Sea floor mapping in 1995 shows a series of large volcanic seamounts stretching westward for nearly 300 km beyond that point. The morphology, spacing, and composition of those sampled are consistent with their having formed as a consequence of eruption of suprasubduction zone arc magmas. The relationships of the volcanoes to the tectonic processes of subduction of the Pacific plate beneath the southern portion of the Mariana convergent plate margin are becoming increasingly clear as new bathymetry and geochemical data are amassed. The volcanoes along this trend that lie closest to Guam are forming where the center of active extension in the back-arc basin intersects the line of arc volcanoes. They develop well-defined rifts that are parallel to rift structures along the extension center, whereas volcanoes of the spreading axis to the north are smaller than the frontal arc volcanoes and tend to form along lineaments. Compositions of lavas from these intersection volcanoes bear some similarities to back-arc basin basalt, but are on the whole well within the range of compositions for Mariana island arc lavas. The Pacific plate subducts nearly orthogonal to the strike of the trench along the southern part of the Mariana system and the distance to the arc line from the trench axis is only ∼ 150 km. Several deep fault-controlled canyons on the inner slope of the southern Mariana trench indicate an enhanced tectonic extension of this plate margin. The presence of these active arc volcanoes and the existence of the orthogonal normal faulting along the southern Mariana forearc supports a model of radial extension for formation of the Mariana Trough, a model previously dismissed because of the lack of evidence of these two major geological features.     

兴都库什及邻近区域空间应力场特征及其构造意义

兴都库什及邻近区域地处印度洋板块和欧亚板块碰撞带的西缘,是大陆内部中源地震最为活跃的区域,各种数据均显示出该区域有着十分特殊的现象.本文从地质构造、地震分布特征、震源机制解、应力场等方面进行初步分析.结果表明,不同的深度应力场方向表现各不相同,不同的区域震源机制特征各异,尤其是正断层性质地震在北东向表现出了线性展布.通过构造模拟认为该区域可能是在地壳的碰撞、推挤、俯冲作用下出现的褶皱,由于地层倒转嵌入,从而形成了多层位地震密集现象.同时在推挤、拖曳的过程中形成了一条深度约100 km以下的北东向的拉张性破裂.     

板块边界构造应力场的反演及其对华北地震的影响研究

利用全球震源机制解资料,采用力轴张量计算法,反演中国大陆附近板块边界线上的构造应力场空间分布,其最大主压应力轴的方位角与GPS研究得到的板块运动方向一致,太平洋板块西边界和菲律宾板块琉球岛弧段的最大主压应力轴的倾角与板块俯冲倾角基本相当,因此认为该方法反演的构造应力场真实可靠。1999年、2005年和2011年太平洋板块日本本州段的最大主压应力轴方位角存在转折现象,震例总结显示该转折现象往往对应华北地区5级以上,甚至6级左右地震,但2011年的转折变化对应华北地震的震级在5级左右。根据对太平洋板块西边界的分段研究,认为2011年的转折变化主要是由42°~50°N段的构造应力场转折引起的,而该段从地理位置结合俯冲方向来看,影响的主要地区是东北地区,而对华北的影响相对较小,因此导致对应地震的震级偏低。1992—2000年菲律宾板块琉球岛弧段的最大主压应力轴方位角存在大幅度、长时间的逆时针偏转现象,分析认为是造成同期华北南部地区发生多次具有典型华南应力场特征地震的原因。