Young,active conjugate strike–slip deformation in West Sichuan: evidence for the stress–strain pattern of the southeastern Tibetan Plateau

The active kinematics of the eastern Tibetan Plateau are characterized by the southeastward movement of a major tectonic unit, the Chuan-Dian crustal fragment, bounded by the left-lateral Xianshuihe–Xiaojiang fault in the northeast and the right-lateral Red River–Ailao Shan shear zone in the southwest. Our field structural and geomorphic observations define two sets of young, active strike–slip faults within the northern part of the fragment that lie within the SE Tibetan Plateau. One set trends NE–SW with right-lateral displacement and includes the Jiulong, Batang, and Derong faults. The second set trends NW–SE with left-lateral displacement and includes the Xianshuihe, Litang, Xiangcheng, Zhongdian, and Xuebo faults. Strike–slip displacements along these faults were established by the deflection and offset of streams and various lithologic units; these offsets yield an average magnitude of right- and left-lateral displacements of ～15–35 km. Using 5.7–3.5 Ma as the time of onset of the late-stage evolution of the Xianshuihe fault and the regional stream incision within this part of the plateau as a proxy for the initiation age of conjugate strike–slip faulting, we have determined an average slip rate of ～2.6–9.4 mm/year. These two sets of strike–slip faults intersect at an obtuse angle that ranges from 100° to 140° facing east and west; the fault sets define a conjugate strike–slip pattern that expresses internal E–W shortening in the northern part of the Chuan-Dian crustal fragment. These conjugate faults are interpreted to have experienced clockwise and counterclockwise rotations of up to 20°. The presence of this conjugate fault system demonstrates that this part of the Tibetan Plateau is undergoing not only southward movement, but also E–W shortening and N–S lengthening due to convergence between the Sichuan Basin and the eastern Himalayan syntaxis.     

青藏高原东北缘大陆岩石圈现今变形和位移

川青地块在地貌上为川西高原,亦是青藏高原东北边缘最重要的构造单元。新的GPS监测资料表明,在欧亚框架内,川青地块及其邻近的龙门山带和华南地块西缘的地壳运动水平速度,具有自西向东由25．66mm／a递变下降到6．99mm／a的总趋势。速度矢量表现出顺时针涡旋转动。川青地块内具有局部应变积累的非均一的区域剪切。横切鲜水河断裂带中段新的GPS量结果揭示,两侧地块间的平均左旋滑动速率约8mm／a;由于局部应变积累,断裂系南西侧的主断裂的移动速率为9．3mm／a,其间为拉分盆地和小的横向伸展断裂。鲜水河断裂系的左旋断裂滑动作用,调节了川青地块与／11滇地块之间的相对运动。     

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.     

SLIP RATE AND RECURRENCE INTERVAL OF STRONG EARTHQUAKE OF QIANNING—KANGDING SEGMENT ON XIANSHUIHE FAULT

SLIP RATE AND RECURRENCE INTERVAL OF STRONG EARTHQUAKE OF QIANNING—KANGDING SEGMENT ON XIANSHUIHE FAULT     

天景山断裂带晚第四纪左旋走滑运动速率确定及其空间分布特征

天景山断裂带是青藏高原东北缘一条重要的左旋走滑边界断裂,但是对该断裂左旋走滑运动速率的空间分布特征缺少足够的研究和认识.通过卫星影像解译和野外地质调查,我们在天景山断裂带中段滑动速率限定范围较宽泛的段落选择两个典型的断错地貌观察点,以期获得更为可靠的断裂晚第四纪滑动速率.首先,利用差分GPS和无人机摄影测量技术分别对孟家湾和崾岘沟两点的冲沟或河流阶地的左旋走滑位移量进行精确测量和恢复.然后,利用光释光测年技术对被断错地貌面的年龄进行限定.最后,在综合分析地貌标志物位移和地貌面年龄之间关系以及其形成演化过程,计算和讨论孟家湾和崾岘沟两个点的滑动速率,分别为(1.2±0.3)mm/a和(0.9±0.3)~(1.1±0.2)mm/a.通过与前人研究结果进行对比和分析,认为天景山断裂带晚第四纪左旋走滑运动速率在空间上较为稳定,约为1.1 mm/a.     

青藏高原大型走滑断裂带晚新生代构造地貌生长及水系响应

大型走滑断裂带对调节印度板块和亚洲板块碰撞后产生的陆内构造变形和地貌生长起着非常重要作用。本文分析了沿青藏高原北缘主要大型左旋走滑断裂带：东昆仑、康西瓦和鲜水河-小江断裂带发育的错断地质体、大型错断水系或水系拐弯等新构造地貌特征,表明这些大型走滑断裂带在晚新生代以来发生了大规模的左旋走滑运动：前新生代地质体错位距离为80～120 km,大型水系累积的位移量可达80～90 km。根据这些走滑断裂带的长期走滑速率为8～12 mm/a,估算上述大型走滑断裂带的左旋走滑运动开始于中新世晚期：东昆仑和康西瓦断裂带左旋走滑运动开始于10±2 Ma; 鲜水河-小江断裂带甘孜-玉树段的左旋走滑运动的开始时间约为8～115 Ma。同样,如果大型水系的沿断裂带出现的大型错位或拐弯能够代表断裂带累积错位的上限,表明发源于青藏高原的黄河、金沙江、喀拉喀什河和玉龙喀什河等一级水系上游大致开始形成于9～7 Ma±。西昆仑山前盆地中河流相沉积的最早响应时间为8～6 Ma,与喀拉喀什河和玉龙喀什河等西昆仑山地区一级水系的形成时间基本一致,表明这些大型水系初始形成时间与左旋走滑构造运动的开始时间准同时。这表明中新世中晚期青藏高原构造演化发生了重要转变。     

LATE QUATERNARY FAULTING OF JIALI FAULT

LATE QUATERNARY FAULTING OF JIALI FAULT1　ChungS ,LoC ,LeeT ,etal.DiachronousupliftoftheTibetanplateaustarting 40Myrago[J].Nature ,1998,394:76 9～773. 2　ColemanM ,HodgesK .EvidenceforTibetanplateauupliftbefore 14Myragofromanewminimumageforeast westexten sion[J].Nature ,1995 ,374:49～ 5 2 . 3　HarlandWB ,ArmstrongRL ,CoxAV ,etal.Ageologictimescale 1989[J].Cambridge ,U .K :CambridgeUnivPress,1990 . 4　HarrisonTM ,CopelandP ,KiddWSF ,etal.RaisingTibet[J].…     

松潘—甘孜地区百年地震构造和现今动力学

研究区位于青藏高原的东北隅(96°～107°E,30°～35°N)。基于该地区长度大于2km的4 781条1∶20万数字化实测断裂、1900年以来的5 220条数字地震记录,以及野外地质观测数据,识别出993条不同属性的地震断层,构建了该地区百年地震构造格局。1970年以来十年期地震断层跃迁图像表明,自20世纪80年代中期白马—虎牙强烈震群爆发之后,地震活动在沿各主要走滑断层带自西(北西)向东(南东)迁移的同时,逐渐向中部贡玛—达曲断裂带和南部鲜水河断裂带的东南段集中。地震活动的断裂构造联系主要表现为挤压剪切转换机制和典型的楔顶效应。研究区165个GPS速度矢量展现了与3个地块和以鲜水河断裂带为主的速度域、速度梯度带和速度扰动区。跨研究区南缘鲜水河断裂带的位移速率因贡玛—达曲断裂带汇聚而达到了6.5～8.6mm/a,而跨北缘东昆仑断裂带的位移速度只有1.8～2.2mm/a。因鲜水河断裂走向在其中南段发生向南的急剧偏转,垂直断层面的位移矢量分量不断增强,形成了汶川8.0级地震成核及NE向单边破裂的动力学条件。     

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。     

滇西北程海—宾川断裂带第四纪分段活动性的构造地貌表现与限定

青藏高原东南部边缘的程海-宾川断裂带是一条正断与左旋走滑运动兼具的复合型活动断裂,起着调节青藏高原内部物质向东挤出的重要作用,并控制着区域的主要强震活动.基于GIS（Geographic Information System）技术,利用遥感影像和DEM（Digital Elevation Model）数据提取该区的关键构造地貌信息,对其第四纪分段活动性及特征进行了分析探讨.结果表明,程海-宾川断裂带的第四纪活动具有明显的分段性及空间差异性.其北段的金官-程海盆地主边界断层以正断层活动性质为主,并具有整个断裂带上最高的垂直活动速率;中段的期纳断裂以左旋走滑运动为主,且具有最高的走滑活动速率;南段宾川盆地东缘边界断裂也以正断层活动为主,但垂直活动速率略低于北段.总体上看,程海-宾川断裂带第四纪期间的垂直活动性由北往南降低,水平走滑活动性由中段往南北两端降低.在活动强度方面,程海-宾川断裂带百万年尺度的长期活动速率一直保持着较为稳定的状态,垂直活动速率主要集中在0.09~0.69 mm/a,水平走滑速率在0.20~1.40 mm/a.整体而言,程海-宾川断裂带中多数断裂的第四纪活动性以"中等"和"弱"为主.但历史地震活动表明,其不同段落上的未来强震活动趋势值得关注,尤其是历史强震活动相对空缺的中南段.      

新疆乌孙山北缘断裂晚第四纪活动及区域构造意义

乌孙山北缘断裂位于新疆伊宁盆地南部,是伊宁盆地与乌孙山的边界断裂,由多条平行或斜列的次级断层组成.断裂呈近东西走向,总体倾向南,山前主断裂主要表现为高角度逆冲,倾角50°~80°,前缘冲断面相对较缓.断裂上盘主要由石炭系-二叠系组成,下盘主要为第四系和侏罗系,断层两盘沉积物的ESR年代表明断裂带多处错断中、上更新统地层.野外地层接触关系和区域构造研究表明,在中更新世末以来,断裂强烈向北逆冲,与伊犁盆地北缘断裂共同控制了盆山地貌格局.伊宁盆地及邻区中更新世末的区域构造运动与青藏高原的共和运动时代相当,这次事件由南北天山向伊犁盆地的对冲挤压引起,动力来源于青藏高原向外扩展生长.      

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。     

Present-day Block Movement and Fault Activity on the Eastern Margin of the Tibetan Plateau

The geology and tectonics in the eastern margin of Tibetan Plateau are complex. The main tectonic framework is composed of blocks and faults. Using discontinuous global positioning system survey data for 2008–2014, the velocity field for the Eurasia reference framework was obtained. Based on the velocity field, the present-day velocities of the blocks and boundary faults were estimated. The results reveal that the movement rates of the Chuan-Qing, South China, Chuan-Dian and Indo-China blocks are(17.02±0.60) mm/a,(8.77±1.51) mm/a,(13.85±1.31) mm/a and(6.84 ± 0.74) mm/a, respectively, and their movement directions are 99.5°, 120.3°, 142.9° and 153.3°, respectively. All blocks exhibit clockwise rotation. The displacement rates of the Xianshuihe, Longmenshan, Anninghe, Zemuhe, Xiaojiang and Red River faults are(7.30±1.25–8.30±1.26) mm/a,(10.07±0.97–11.79±0.89) mm/a,(0.96±0.74–2.98±1.73) mm/a,(2.03±0.49–3.20±0.73) mm/a,(3.45±0.40–6.02±0.50) mm/a and(6.23±0.56) mm/a, respectively. The Xianshuihe, Anninghe, Zemuhe and Xiaojiang faults show leftlateral strike-slip movement, while the Longmenshan and Red River faults show right-lateral strikeslip. These characteristics of the blocks and faults are related to the particular tectonic location and dynamic mechanism.     

Late-Quaternary Slip Rate and Seismic Activity of the Xianshuihe Fault Zone in Southwest China

The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight Ms ≥ 7.0 earthquakes. The seismic risk of the Xianshuihe fault zone is a large and realistic threat to the western Sichuan economic corridor. Based on previous studies, we carried out field geological survey and remote sensing interpretation in the fault zone. In addition, geophysical surveys, trenching and age-dating were conducted in the key parts to better understand the geometry, spatial distribution and activity of the fault zone. We infer to divide the fault zone into two parts: the northwest part and the southeast part, with total eight segments. Their Late Quaternary slip rates vary in a range of 11.5 mm/a –(3±1) mm/a. The seismic activities of the Xianshuihe fault zone are frequent and strong, periodical, and reoccurred. Combining the spatial and temporal distribution of the historical earthquakes, the seismic hazard of the Xianshuihe fault zone has been predicted by using the relationship between magnitude and frequency of earthquakes caused by different fault segments. The prediction results show that the segment between Daofu and Qianning has a possibility of Ms ≥ 7.0 earthquakes, while the segment between Shimian and Luding is likely to have earthquakes of about Ms 7.0. It is suggested to establish a GPS or In SAR-based real-time monitoring network of surface displacement to cover the Xianshuihe fault zone, and an early warning system of earthquakes and post seismic geohazards to cover the major residential areas.     

Active strike-slip faulting history inferred from offsets of topographic features and basement rocks: a case study of the Arima–Takatsuki Tectonic Line,southwest Japan

Geological, geomorphological and geophysical data have been used to determine the total displacement, slip rates and age of formation of the Arima–Takatsuki Tectonic Line (ATTL) in southwest Japan. The ATTL is an ENE–WSW-trending dextral strike-slip fault zone that extends for about 60 km from northwest of the Rokko Mountains to southwest of the Kyoto Basin. The ATTL marks a distinct topographic boundary between mountainous regions and basin regions. Tectonic landforms typically associated with active strike-slip faults, such as systematically-deflected stream channels, offset ridges and fault scarps, are recognized along the ATTL. The Quaternary drainage system shows progressive displacement along the fault traces: the greater the magnitude of stream channel, the larger the amount of offset. The maximum dextral deflection of stream channels is 600–700 m. The field data and detailed topographic analyses, however, show that pre-Neogene basement rocks on both sides of the ATTL are displaced by about 16–18 km dextrally and pre-Mio–Pliocene elevated peneplains are also offset 16–17 km in dextral along the ATTL. This suggests that the ATTL formed in the period between the development of the pre-Mio–Pliocene peneplains and deflection of the Quaternary stream channels.The geological, geomorphological and geophysical evidence presented in this study indicates that (1) the ATTL formed after the mid-Miocene, (2) the ATTL has moved as a dextral strike-slip fault with minor vertical component since its formation to late Holocene and (3) the ATTL is presently active with dextral slip rates of 1–3 mm/year and a vertical component of >0.3 mm/year. The formation of the ATTL was probably related to the opening of the Japan Sea, which is the dominant tectonic event around Japan since mid-Miocene. The case study of the ATTL provides insight into understanding the tectonic history and relationship between tectonic landforms and structures in active strike-slip faults.     

Neotectonics of the Eastern Margin of the Tibetan Plateau: New Geological Evidence for the Change from Early Pleistocene Transpression to Late Pleistocene-Holocene Strike-slip Faulting

We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred during the Early Pleistocene, evidenced by eastward thrusting of Mesozoic carbonates on the Pliocene lacustrine deposits along the Minjiang upstream fault zone and by development of the transpressional ridges of basement rocks along the Anninghe river valley. The Middle Pleistocene seems to be a relaxant stage with local development of the intra-mountain basins particularly prominent along the Minjiang Upstream and along the southern segment of the Anninghe River Valley. This relaxation may have been duo to a local collapse of the thickened crust attained during the late Neogene to early Pleistocene across this marginal zone. Fault kinematics has been changed since the late Pleistocene, and was predominated by reverse sinistral strike-slip along the Minshan Uplift, reverse dextral strike-slip on the Longmenshan fault zone and pure sinistral strike-slip on the Anninghe fault. This change in fault kinematics during the Quaternary allows a better understanding of the mechanism by which the marginal ranges of the plateau has been built through episodic activities.     

Late Quaternary Tectonic Deformation of the Eastern End of the Altyn Tagh Fault

The Quaternary activity of the faults at the eastern end of the Altyn Tagh fault, including the Dengdengshan–Chijiaciwo, Kuantanshan and Heishan faults, was studied on the basis of interpretation of satellite images, trenching, geomorphologic offset measurements and dating. The Altyn Tagh fault has extended eastwards to Kuantanshan Mountain. The left–slip rates of the Altyn Tagh fault decreased through the Qilianshan fault and were transformed into thrust and folds deformation of many NW–trending faults within the Jiuxi basin. Meanwhile, under NE–directed compression of the Tibetan plateau, thrust dominated the Dengdengshan–Chijiaciwo fault northeast of the Kuantanshan uplift with a rate lower than that of every fault in the Jiuxi basin south of the uplift, implying that tectonic deformation is mainly confined to the plateau interior and the Hexi Corridor area. From continual northeastward enlargement of the Altyn Tagh fault, the Kuantanshan uplift became a triangular wedge intruding to the east, while the Kuantanshan area at the end of this wedge rose up strongly. In future, the Altyn Tagh fault will continue to spread eastward along the Heishan and Jintananshan faults. The results have implications for understanding the propagation of crustal deformation and the mechanism of the India–Eurasian collision.     

Crustal Motion Characteristics in the Eastern Margin of the Tibetan Plateau and Adjacent Regions after the Wenchuan Earthquake

The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the Eurasia reference framework has been obtained, and the general trend of contemporary crustal motion after the occurrence of the Wenchuan earthquake has been studied.In addition, using the velocity field, the block movement velocity has been estimated by least-squares fitting.Furthermore, the properties and displacement rates of main faults have been obtained from the differences in velocity vectors of the blocks on both sides of the faults.The results reveal that there are no obvious changes in the general characteristics of crustal motion in this area after the Wenchuan earthquake.The earthquake mainly changed the rate of the movement of the Chuan-Qing block and caused variation in the movement direction of the South China block.The effect of the earthquake on faults is mainly reflected in variations in fault displacement velocity; there is no fundamental change in the properties of fault activity.The displacement rates of the Xianshuihe fault decreased by 3–4 mm/a, the Longmenshan fault increased by 9–10 mm/a, and the northern segment of the Anninghe fault increased by approximately 9 mm/a.Furthermore, the displacement rates of the Minjiang, Xueshan, Huya, Longquanshan, and Xinjin faults increased by 2–3 mm/a.This implies that the effects of the Wenchuan earthquake on crustal movement can mainly be observed in the Chuan-Qing, South China, and N-Chuan-Dian blocks and their internal faults, as well as the Xianshuihe and Longmenshan faults and the northern section of the Anninghe fault.The reason for this is that the Wenchuan earthquake disturbed the kinematic and dynamic balance in the region.     

西秦岭西段光盖山-迭山断裂带坪定-化马断裂的新活动性与滑动速率

位于西秦岭西段的光盖山-迭山断裂带是由3条近平行的断裂所组成,其中坪定-化马断裂是该断裂带的主断层。坪定-化马断裂以宕昌岷江为界分为东、西两段,西段的新活动性明显强于东段。断裂西段线性特征明显,可见清晰的断层崖,不同期次的洪积扇上均有断层陡坎发育,晚第四纪以来有过明显的活动,最新一次活动的离逝时间约为1kaB.P.左右。通过对断错地貌研究得到断裂晚第四纪以来的垂直滑动速率为 0.49±0.08~1.15±0.28mm/a,左旋滑动速率为 0.51±0.13mm/a。而断裂东段由多条斜交或近于平行的断裂所组成,活动性明显减弱,没有发现最新活动的证据。在地貌上多表现为线性沟谷,向东逐渐被褶皱所替代,从基岩断面及相关地貌特征来看断裂活动性质主要表现为逆冲兼具左旋走滑运动。     

川西理塘断裂带的空间展布与第四纪左旋走滑活动的遥感影像标志

遥感技术具有宏观性、直观性、时效性以及不受其他外部因素制约的特点,在活动断裂的研究中具有很大的优势。文章在系统总结活动断裂的遥感影像标志的基础上,综合利用Landsat ETM、ALOS、Google earth及ASTER GDEM(ASTER全球数字高程模型)等影像资料,结合前人研究成果及关键地段的野外实地考察,对展布于青藏高原东南缘之藏东-川西高原地区的理塘左旋走滑活动断裂带进行了详细分析与研究,结果显示该断裂带整体呈不连续的北西-南东向弧形展布,全长可达400km左右。根据该断裂的几何展布对其进行分段,自北西向南东可分五段,依次为:卡贡断裂、章德断裂、毛垭坝断裂、理塘断裂及康嘎-德巫断裂。综合分析不同断裂段的影像特征、错断地貌特征及现代地震活动情况表明,整条断裂带南段的毛垭坝-理塘-德巫断裂段的影像特征最明显、最连续,活动性明显较北段显著,这一特征可能暗示青藏高原内部物质向东挤出的速率有自西向东加快的趋势。