Active Faulting Pattern,Present‐day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

Abstract: This paper examines major active faults and the present-day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region. It shows that the East Tibetan Plateau is dominated by strike-slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field, except for the west Qinling range where it parallels the striking of the major strike-slip faults. Active tectonics in the East Tibetan Plateau is characterized by three faulting systems. The left-slip Kunlun-Qinling faulting system combines the east Kunlun fault zone, sinistral oblique reverse faults along the Minshan range and two major NEE-striking faults cutting the west Qinling range, which accommodates eastward motion, at 10–14 mm/a, of the Chuan-Qing block. The left-slip Xianshuihe faulting system accommodated clockwise rotation of the Chuan-Dian block. The Longmenshan thrust faulting system forms the eastern margin of the East Tibetan Plateau and has been propagated to the SW of the Sichuan basin. Crustal shortening across the Longmenshan range seems low (2–4 mm/a) and absorbed only a small part of the eastward motion of the Chuan-Qing block. Most of this eastward motion has been transmitted to South China, which is moving SEE-ward at 7–9 mm/a. It is suggested from geophysical data interpretation that the crust and lithosphere of the East Tibetan Plateau is considerably thickened and rheologically layered. The upper crust seems to be decoupled from the lower crust through a décollement zone at a depth of 15–20 km, which involved the Longmenshan fault belt and propagated eastward to the SW of the Sichuan basin. The Wenchuan earthquake was just formed at the bifurcated point of this décollement system. A rheological boundary should exist beneath the Longmenshan fault belt where the lower crust of the East Tibetan Plateau and the lithospheric mantle of the Yangze block are juxtaposed.     

大陆构造变形与地震活动——以青藏高原为例

大陆内部构造变形和地震活动往往突显出复杂的、区域性的特征,很难用板块构造理论来解释。青藏高原是大陆构造变形的典型实例,具有不同构造变形的分区特征,不仅表现在物质组成、地形地貌和断裂组合等方面的不同,而且还表现出不同的地震活动特征。东昆仑断裂带以北的青藏高原北部地块,主要发育一系列挤压环境下的盆岭构造,表现为以连续变形为特征的上地壳挤压缩短变形;高原中北部巴颜喀拉地块,具有整体向东运动的特点,变形主要集中在其边缘,表现为刚性块体运动特征。在东部,由于稳定的四川盆地(扬子地块)的阻挡,位于龙日坝和龙门山断裂带之间相对坚硬的龙门山地区受到东西向强烈挤压,西部边界为伸展变形;在高原中央腹地羌塘地块西部,由于上地壳物质在向东挤出的驱动下不断变形,沿一系列小型正断层和走滑断层以伸展变形为主,表现为弥散型变形特征。相比之下,羌塘地块的东部向东-南东方向挤出,在大型走滑断层之间形成一个刚性块体;高原南部地块以东西向伸展的南北向裂谷系为主要变形特征,高原南缘以南北向挤压的大型逆冲断裂系为特征。历史地震和仪器记录的大地震(M≥8)只发生在高原东北和东南部的大型走滑带,以及东部和南部边缘的大型逆冲断裂上,沿后者更为频发。到目前为止,高原其他地区只发生了8级以下地震。青藏高原这种分区域的地壳变形形式和地震活动分布是大陆构造变形的重要特征。     

粘弹性数值模拟龙门山断裂带应力积累及大震复发周期

2008年5月12日在低地形变速率的龙门山断裂带上突发汶川强震,引发人们对该地震孕震机制的思考。本文根据GPS观测资料确定边界条件,通过三维粘弹性数值模拟探讨了汶川地震的孕震机理,计算了该区域岩石圈的应力增加速率和积累过程,以及汶川地震同震应力变化与震后应力松弛,在此基础上估算了汶川8.0级大地震的复发周期。数值模拟结果表明:印度板块对欧亚板块的推挤造成青藏高原的物质东流,高原中、下地壳物质在龙门山断裂带处遭到相对坚硬的四川盆地的阻挡之后,部分中、下地壳物质在龙门山断裂带下堆积产生应力集中。两个重要因素为应力集中提供了重要控制作用:其一是青藏高原中、下地壳较低的粘滞系数与四川盆地中、下地壳较高的粘滞系数的差异,其二是从青藏高原到四川盆地的Moho面深度在龙门山断裂带的突变。低应变速率的龙门断裂带岩石圈在数千年时间尺度的应力积累过程中,脆性上地壳的应力随时间近乎线性增长,并且上地壳深部的应力增长率超过浅部,6000年内应力积累最大量达到-21.6MPa,应力增长速率为-0.0036MPa/a;而柔性的中、下地壳以及岩石圈上地幔的应力在增长一段时间之后趋于稳定。在空间上,龙门山断裂带受到的压应力从断层西南向北东方向逐渐减小,而剪应力从西南到北东方向逐渐增大,应力状态有利于地震发生时断层的破裂方式从西南的逆冲运动向北东的逆冲兼走滑运动的方式发展。通过应力积累与地震应力降的计算得到汶川8.0级大地震的复发周期约为5400年。     

青藏高原东缘地壳上地幔结构及其动力学意义

本文综述了我们在青藏高原东缘实施的垂直切过龙门山断裂带宽频带地震探测的研究成果,揭示了研究区复杂的地壳上地幔结构,结果表明松潘-甘孜地块与四川盆地西缘莫霍面深度为58 km与40 km±,在龙门山断裂带下方存在约15 km的莫霍面错断; 松潘-甘孜与龙门山断裂带域地壳纵横波速度比Vp/Vs比值远大于173,预示着粘性下地壳流或基性/超基性物质的存在。探讨了研究区强烈的盆山之间以及深部不同层圈之间的相互作用,推断四川盆地对青藏高原东缘软流圈驱动的物质东向逃逸阻挡作用可能深达整个上地幔。     

青藏高原东部晚新生代重大构造事件与挤出造山构造体系

文章系统梳理了青藏高原东部地区晚新生代重大构造事件的沉积记录、岩浆记录和构造变形响应,重新厘定了青藏运动或横断事件的起始时限,建立了青藏高原东部晚新生代构造演化序列与挤出造山构造体系。研究认为,发生在上新世之前的青藏运动是青藏高原东部最重要的构造作用阶段,起始于距今12~8 Ma,并持续到上新世早期,持续时间达6~8 Ma。在这个构造运动阶段,青藏高原东部地块(川滇地块、川青地块、西秦岭构造带和陇中地块等)有序地向东挤出,受到鲜水河、东昆仑、海原等WNW-ESE向大型断裂左旋走滑运动调节,构造挤出同时伴随地块内部逆冲褶皱变形,导致地壳增厚和高原东缘山脉快速崛起;构造挤出也超越了现今东缘地貌边界,向东扩展导致扬子地块盖层滑脱褶皱,形成龙泉山、大凉山等褶皱构造带。上新世出现的砾石层(东缘前陆地带的大邑砾石层、临夏盆地的积石砾石层、兰州盆地的五泉砾石层等)标志了青藏高原东部差异性构造地貌的形成。上新世晚期至早更新世时期(3.6~1.0 Ma)对应一个构造松弛阶段,青藏高原东部整体进入冰冻时期,沿其东缘发育一系列受正断层控制的南北向伸展断陷盆地,如安宁河谷地、元谋盆地、盐源盆地、滇西北盆地群等,其中加积了以昔格达组为代表的稳定河湖相沉积。发生在早、中更新世之交(距今1.0~0.6 Ma)的昆—黄运动或元谋事件使青藏高原东部地块进一步向东挤出、东缘地壳逆冲增厚和年轻山系加速隆升。晚更新世以来的构造运动称为共和运动或最新构造变动阶段,起始于距今约120 ka,青藏高原东缘构造变形系统出现重大分化,南段川滇菱形地块发生绕喜玛拉雅东构造结的顺时针旋转运动,形成川滇双弧形旋扭构造体系;而中段川青地块的挤出伴随东缘龙门山断裂带的右旋走滑运动和秦岭山系的向东挤出。在这个最新构造变动阶段,青藏高原东部下地壳通道流可能是重要的深部构造驱动因素。     

全球定位系统测量与青藏高原东部流变构造

通过1991～1997年期间高精度全球定位系统测量,建立了青藏高原东部及其邻区的现代地壳运动速度场。相对成都,鲜水河-小江断裂以西的藏东-滇中地区的运动速度变动在1．57～17．49mm／a之间,总体为8mm／a以上。该断裂以东地区的运动速度小,约为0～7mm／a。在此基础上,通过对围绕东喜马拉雅构造结的涡旋和川西地区的涡旋的认定,以及它们在地壳变形中的作用的分析,阐述了青藏高原东部及其邻区深部物质流变的主要形式和地壳流变构造。     

四川盆地西北部新生代构造变形模式讨论——对认识青藏高原东北缘新生代变形机制的意义

综合造山带内的构造热年代学及盆地内部进行的磷灰石裂变径迹研究,提出了四川盆地西北部的三个背斜（潼梓关背斜、九龙山背斜和南阳坝背斜）主要是新生代构造变形的产物。野外观察发现汉中盆地是一个第四纪的拉分盆地,其主控断层具左行走滑性质。新生代青藏高原东缘大型地块向东挤出,遭遇强硬的四川克拉通阻挡之后,沿着龙门山形成了一个右行的走滑挤压带,并且影响到邻近的四川盆地,形成北东向背斜。这期构造变形往北延伸进入米仓山,形成具有逆冲性质的北东向断层。四川盆地北面也存在向东的挤出作用,这和汉中盆地主控断层的左行走滑性质是匹配的。四川盆地北面的地块挤出影响了米仓山前缘的四川盆地,由于龙门山和米仓山构造变形的叠加,使得最东面的南阳坝背斜相对于其它两个背斜在褶皱轴上发生了偏转。     

西秦岭地区东昆仑-秦岭断裂系晚新生代左旋走滑历史及其向东扩展

要通过在TM遥感图像解译和野外观测的基础上,描述了东昆仑断裂带东段活动形迹的组成和活动断层地貌特征,阐述了甘南高原西秦岭地区新近纪拉分盆地的沉积-构造特征,提出了该区东昆仑-秦岭断裂系晚新生代左旋走滑伸展-走滑挤压-走滑伸展的3个阶段的构造变形模式。指出,中新世晚期至上新世早期,东昆仑-秦岭断裂系以左旋走滑伸展活动为主,伴随着西秦岭地区拉分盆地的形成和超基性火山岩群的发育。这期左旋走滑伸展活动向东扩展导致了渭河盆地新近纪引张应力方向由早期的NE-SW向转变为晚期的NW—SE向。上新世晚期以来(约3．4Ma以前),东昆仑-秦岭断裂系以左旋走滑挤压活动为主,导致早期拉分盆地的轻微褶皱变形,走滑挤压活动主要集中在东昆仑东段玛沁-玛曲主断裂带上。该期构造变动持续到早更新世,它的向东扩展产生了广泛的地壳形变效应,包括青藏东缘岷山隆起带的快速崛起、华北地区汾-渭地堑系的形成和发展以及郯庐断裂带右旋走滑活动等。中、晚更新世时期,断裂系以走滑伸展变形为主,主要集中在东昆仑断裂带东段3个分支上,地块向东挤出伴随着顺时针旋转。     

青藏高原东南部第四纪右旋剪切运动

通过对藏东南嘉黎断裂和滇西北断裂实地考察研究，表明青藏高原南部不存在统一的边界走滑断裂。嘉黎断裂的西段位于青藏高原南部，是一个南北挤压作用下的东西向伸展构造区，发育近南北向的地堑系，嘉黎断裂西段是这些地堑之间的转换断层，具有较高的右旋走滑速率。滇西北断裂与红河断裂构成川滇菱形块体的西南边界，该块体具有向东南逃逸和顺时针旋转运动。     

Late Cenozoic transtensional fault belt discovered on the boundary of the Awati Sag in the northwestern Tarim Basin

Late Cenozoic transtensional fault belt was discovered on Shajingzi fault belt, NW boundary of the Awati Sag in the northwestern Tarim Basin. And numerous Quaternary normal faults were discovered on Aqia and Tumuxiuke fault belts, SW boundary of Awati. This discovery reveals Quaternary normal fault activity in the Tarim Basin for the first time. It is also a new discovery in the southern flank of Tianshan Mountains. Shajingzi transtensional fault belt is made up of numerous, small normal faults. Horizontally, the normal faults are arranged in right-step, en echelon patterns along the preexisting Shajingzi basement fault, forming a sinistral transtensional normal fault belt. In profile, they cut through the Paleozoic to the mid-Quaternary and combine to form negative flower structures. The Late Cenozoic normal faults on the SW boundary of Awati Sag were distributed mainly in the uplift side of the preexisting Aqia and Tumuxiuke basement-involved faults, and combined to form small horst and graben structures in profile. Based on the intensive seismic interpretation, careful fault mapping, and growth index analysis, we conclude that the normal fault activity of Shajingzi transtensional fault belt began from Late Pliocene and ceased in Late Pleistocene (mid-Quaternary). And the normal faulting on the SW boundary of Awati Sag began from the very beginning of Quaternary and ceased in Pleistocene. The normal faulting on Awati’s SW boundary began a little later than those on the NW boundary. The origin of Shajingzi transtensional normal fault belt was due to the left-lateral strike-slip occurred in the southern flank of Tianshan, and then, due to the eastward escape of the Awati block, a tensional stress developed the normal faults on its SW boundary.     

2008年5月12日汶川地震（Ms8.0）地表破裂带的分布特征

2008年5月12日14时28分,青藏高原东缘龙门山地区（四川汶川）发生了Ms8.0级地震。震后野外考察表明,5.12汶川地震发生在NE走向的龙门山断裂带上,该断裂带晚新生代以来的逆冲速率小于1mm/a,GPS观察结果表明其缩短速率小于3mm/a。这次5.12汶川地震造成了多条同震逆冲地表破裂带,总体长约275km,宽约15km,发震断裂机制主要为逆冲作用（由NW向SE逆冲）伴随右旋走滑。地表主破裂带沿龙门山断裂带的映秀—北川断裂发育,长约275km,笔者称为映秀—北川破裂带,破裂带具有逆冲兼右旋走滑性质。地表次级破裂带沿龙门山断裂带的前缘断裂安县—灌县断裂南段发育,长80km,笔者称为汉旺破裂带,破裂带基本为纯逆冲性质。在这两条破裂带之间发育两条更次一级的同震地表破裂带：一条长约20km呈NE走向的地表破裂带,笔者称为深溪沟破裂带,由于这条破裂带靠近主破裂带南段,并且与主破裂带变形特征一致,因此,笔者将深溪沟破裂带划归映秀—北川破裂带;另一条长约6km呈NW走向、由SW向NE逆冲并兼有左旋滑动的地表破裂带,笔者称为小鱼洞破裂带,它连接映秀—北川破裂带和汉旺破裂带,成为侧向断坡。另外,在灌县—安县断裂东侧的四川盆地内,由都江堰的聚源到江油发育一条NE向的沙土液化带,它可能是四川盆地西部深部盲断裂活动的结果。同震地表破裂带的分布特征表明,龙门山断裂带活动断裂具有强烈的逆冲作用并伴随较大的右旋走滑,断裂向四川盆地扩展。在龙门山断裂带上类似2008年5月12日Ms8.0汶川大地震的强震复发周期为3000～6000a。     

Uniform Strike-Slip Rate along the Xianshuihe-Xiaojiang Fault System and Its Implications for Active Tectonics in Southeastern Tibet

Recent studies on the Xianshuihe-Xiaojiang fault system suggest that the Late Quaternary strike-slip rate is approximately uniform along the entire length of the fault zone, about 15±2 mm/a. This approximately uniform strike slip rate strongly supports the clockwise rotation model of the southeastern Tibetan crust. By approximating the geometry of the arc-shaped Xianshuihe-Xiaojiang fault system as a portion of a small circle on a spherical Earth, the 15±2 mm/a strike slip rate corresponds to clockwise rotation of the Southeastern Tibetan Block at the (5.2±0.7)×10-7 deg/a angular velocity around the pole (21°N, 88°E) relative to the Northeast Tibetan Block. The approximately uniform strike slip rate along the Xianshuihe-Xiaojiang fault system also implies that the Longmenshan thrust zone is not active, or at least its activity has been very weak since the Late Quaternary. Moreover, the total offset along the Xianshuihe-Xiaojiang fault system suggests that the lateral extrusion of the Southeastern Tibetan Block relative to Northeastern Tibetan Block is about 160 km and 200-240 km relative to the Tarim-North China block. This amount of lateral extrusion of the Tibetan crust should have accommodated about 13-24% convergence between India and Eurasia based on mass balance calculations. Assuming that the slip rate of 15±2 mm/a is constant throughout the entire history of the Xianshuihe-Xiaojiang fault system, 11±1.5 Ma is needed for the Xianshuihe-Xiaojiang fault system to attain the 160 km of total offset. This implies that left-slip faulting on the Xianshuihe-Xiaojiang fault system might start at 11±1.5 Ma.     

The Deep Geophysical Structure of the Middle Section of the Longmen Mountains Tectonic Belt and its Relation to the Wenchuan Earthquake

Investigation of the deep geophysical structure of the Longmen Mountains tectonic belt and its relation to the Wenchuan Earthquake is important for the study of earthquakes. By using magnetotelluric sounding profiles of the Luqu–Zhongjiang and Anxian–Suining; seismic sounding profiles of the Sichuan Maowen–Chongqing Gongtan, the Qinghai Huashi Gorge–Sichuan Jianyang, and the Batang–Zizhong; and magnetogravimetric data of the Longmen Mountains region, the deep geophysical structure of the Songpan–Ganzi block, the western Sichuan foreland basin, and the Longmen Mountains tectonic belt and their relation was discussed. The eastward extrusion of the Qinghai–Tibet Plateau thrusts the Songpan–Ganzi block upon the Yangtze block, which obstructs the eastward movement of the Qinghai–Tibet Plateau. The Maoxian–Wenchuan, Beichuan–Yingxiu, and Anxian–Guanxian faults of the Longmen Mountains fault belt dip to northwest with different dip angles and gradually converge in the deeper parts. Geophysical structure suggests that an intracrustal low-velocity, low-resistivity, and high-conductivity layer is common between the middle and upper crust west of the Longmen Mountains tectonic belt but not in the upper Yangtze block. The Sichuan Basin has a thick low-resistance sedimentary layer on a stable high-resistance basement; moreover, there are secondary paleohighs and depression structures at the lower part of the western Sichuan foreland basin with characteristic of high magnetic anomalies, whereas the Songpan–Ganzi block has a high resisitivity cover of upper crust and continues to a low-resistance layer. Considering the Longmen Mountains tectonic belt as the boundary, there are Bouguer gravity anomalies of "one belt between two zones." Thus, we infer that there is a corresponding relation between the inferred crystalline basement of the Songpan block and the underlying basin basement of the Longmen Mountains fault belt. Furthermore, there may be an extensive ancient Yangtze block, which is west of the Ruoergai block. In addition, the crust–mantle ductile shear zone under the Longmen Mountains tectonic belt is the main fault, whereas the Beichuan–Yingxiu and Anxian–Guanxian faults at the surface are earthquake faults. The Wenchuan Ms 8.0 earthquake might be attributed to the collision of the Yangtze block and the Qinghai–Tibet Plateau. The eastward obduction of the eastern edge of the Qinghai–Tibet Plateau and eastward subduction of its deeper part under the influence of the collision of the Indian, Pacific, and Philippine Plates with the Eurasia Plate might have caused the Longmen Mountains tectonic belt to cut the Moho and extend to the middle and upper crust; thus, creating high stress concentration and rapid energy release zone.     

青藏高原东北缘固关-虢镇断裂中段第四纪以来活动特征

固关-虢镇断裂是青藏高原东北缘、鄂尔多斯地块西南缘陇县-宝鸡断裂带中的一条主要断裂,该断裂的运动特征和活动性包含了青藏高原向东北方向扩展机制的重要信息。固关-虢镇断裂中段在卫星影像和DEM图上都显示出清晰的线性影像特征,地貌上表现为清楚的地貌陡坎,陡坎高80～100 m。通过卫星影像判读、野外调查、探槽开挖和年龄测试等方法的综合研究,结果认为固关-虢镇断裂中段第四纪早期有明显活动,并以左旋走滑运动为主,左旋走滑运动利用了早白垩世形成的正断层面;晚更新世以后固关-虢镇断裂停止了活动。造成断裂运动方式和活动性转变的原因是,第四纪以来印度-欧亚大陆碰撞的远程效应到达青藏高原东北缘之后,陇县-宝鸡断裂带周围的块体因为相互作用进行调整,形成了该断裂带局部构造应力以剪应力为主所致。     

青藏高原东缘新构造及其对汶川地震的控制作用

基于卫星遥感图像解译、地形起伏度分析和地面调查资料,论述了青藏高原东缘构造地貌格局、新构造演化阶段和活动断裂特征,提出青藏高原东缘不同地块在晚新生代时期有序的向东挤出过程,并划分为4个阶段：中新世早期川滇地块向北东挤出、中新世晚期川滇地块的再次强烈向东挤出、上新世至早中更新世时期川青地块的向东挤出、晚更新世以来最新构造变动阶段,青藏高原东缘地貌边界带也经历了由西向东、由南向北的有规律的迁移过程。基于活动构造的最新研究成果和现今GPS测量成果,阐述了东昆仑岷山龙门山走滑逆冲断裂系统的运动学特征。根据地震破裂构造的实地调查,分析了汶川地震的地表破裂行为,提出了汶川地震的发震构造模型。研究认为,青藏高原东部地区NW向楔状条块向东运动速度的一半被鲜水河断裂及其北西延伸的构造带所吸收,而龙门山构造带向东运动受阻于四川盆地之下扬子刚性地块,使得龙门山断裂带处在低应变、高应力环境下,因长期应力应变累积而导致向西陡倾的断裂带突然向东逆冲运动而释放能量。汶川强震发生的深部机理值得深入研究。     

2017年8月8日四川九寨沟7.0级地震发震构造浅析

2017年8月8日21时19分,四川阿坝州九寨沟县发生7.0级地震,震中位于巴颜喀拉块体东边界虎牙断裂和东昆仑断裂带东段塔藏断裂交汇区域,地震构造背景较为复杂。地震导致了房屋和道路破坏、滑坡崩塌。根据高分辨率卫星影像解译、阶地坎变形的测量和测年数据得到：塔藏断裂东段晚第四纪以来以左旋走滑为主,兼逆分量,水平滑动速率为2.7~4.1 mm/yr,垂直滑动速率为0.56~0.6 mm/yr。结合此次地震的主余震分布、主震震源机制解等综合结果,初步建立了三维发震构造模型,分析认为此次地震属于走滑型地震,主破裂倾角57°~77°,发震断层可能是塔藏断裂的一条分支,是青藏高原块体向东推挤的一次地震事件。基于历史地震、活动断裂和形变观测方面的研究,巴颜喀拉块体具备显著的强震构造背景,对于该块体边界带周缘的强震活动和变形需要继续关注。     

巽他弧北部掸邦高原地壳变形、长期块体运动和发震过程:来自大地测量研究结果的约束

本文通过约束大地测量研究来探索掸邦高原及其周围地区现今的地壳变形和长期块体运动,以期提供该地区地球动力学和相关地震危险状况的最新状态。掸邦高原在横向上由西侧的萨干(Sagaing)断裂和东侧的红河断裂这两条主要断裂包围。其中,青藏高原地壳的韧性流挤压被认为是该夹层变形单元变形的主要因素。大地测量清楚地表明,萨干断裂和红河断裂段分别具有约18 mm/a和约45 mm/a右旋运动走滑速率。此外,掸邦高原内部断层体系大地滑移累积表现为1213 mm/a的整体左旋运动速率。我们认为相对于刚性巽他古陆,研究区域的形变分布和长期块体运动主要受区域书架型断层作用控制,其原因是掸邦高原两侧的主断裂(萨干断裂和红河断裂)存在差异性断裂活动。     

华北地区上新世至第四纪断裂作用型式与左旋扩展

华北地区包含两个新生代引张构造域,即太行山以西的鄂尔多斯周缘地堑系和以东的华北－渤海平原盆地。鄂尔多斯周缘地堑系上新世～第四纪的断裂作用表征为正向倾滑活动为主,同时具有右旋或左旋走滑分量的运动型式,指示了ＮＷ－ＳＥ向地壳引作用,华北－渤海盆地内上新世～第四纪的断裂作用发生在ＮＮＥ至ＮＥ走向的断鲜明带上,具有右旋和正向倾滑的斜向运动特征,ＥＷ走向的秦岭断裂系华北引张构造域的东界,表现为右旋走滑,与Ｅ     

Compressive Tectonics around Tibetan Plateau Edges

Various earthquake fault types, mechanism solutions, stress field, and other geophysical data were analyzed for study on the crust movement in the Tibetan plateau and its tectonic implications. The results show that numbers of thrust fault and strike-slip fault type earthquakes with strong compressive stress near NNE-SSW direction occurred in the edges around the plateau except the eastern boundary. Some normal faulting type earthquakes concentrate in the Central Tibetan plateau. The strikes of fault planes of thrust and strike-slip faulting earthquakes are almost in the E-W direction based on the analyses of the Wulff stereonet diagrams of fault plane solutions. This implies that the dislocation slip vectors of the thrust and strike-slip faulting type events have quite great components in the N-S direction. The compression motion mainly probably plays the tectonic active regime around the plateau edges. The compressive stress in N-S or NE-SW directions predominates earthquake occurrence in the thrust and strike-slip faulting event region around the plateau. The compressive motion around the Tibetan plateau edge is attributable to the northward motion of the Indian subcontinent plate. The northward motion of the Tibetan plateau shortened in the N-S direction encounters probably strong obstructions at the western and northern margins.     

青藏高原东北缘岩石圈缩短变形——深地震反射剖面再处理提供的证据

青藏高原是由印度板块和亚洲板块于50～60 Ma碰撞而形成的全球最高最大的高原,已成为多数国内外学者的共识.然而,关于它的岩石圈变形机制却是长期争论的问题.深地震反射剖面是精细揭示岩石圈结构、分辨变形样式的有效技术.重新处理的松潘地块一西秦岭造山带深地震反射剖面揭示出岩石圈变形的细节,以地壳上部的双重逆冲构造、地壳中部...