Geomorphic response to growing fault-related folds: example from the foothills of central Taiwan

In this paper we concentrate particularly on the geomorphological indicators left by active tectonics. In the central foothills of Taiwan, we used topography, drainage pattern and structural data to perform quantitative morphometric analysis and to determine relative age of fault-related anticlines. The Tiehchen, Tatu and Pakua ridge belt is a fault-related anticline system located in the hanging wall of the Changhua fault along the western thrust front of the foothills. Geomorphic systems are analysed with intent to detect the various responses of landforms and drainage pattern to late Quaternary deformation. Topography and drainage basin register uplift and are valuable tools to discriminate lateral propagation of an active frontal fold. Geomorphic field evidence and quantitative morphometric parameters are used to define the evolution of the rising anticline ridges and to infer tectonism style along an active front. Geometry of alluvial fans, formed along the frontal side of the anticlines, and weathered terrace deposits provide relevant information on neotectonics. Knowledge concerning these younger anticline ridges, makes this area a good example of an actively forming mountain front. We discuss in detail the origin of N045°, N095 and N120° trending oblique fault scarps which delimite numerous fault blocks. The fault scarps morphology is characterized by imbricate talus facets. Steeper topography accompanied by breaks in the slope along some transverse profiles, seems to correspond to the traces of successive uplifts.     

Geomorphic response to growing fault-related folds: example from the foothills of central Taiwan

Abstract

In this paper we concentrate particularly on the geomorphological indicators left by active tectonics. In the central foothills of Taiwan, we used topography, drainage pattern and structural data to perform quantitative morphometric analysis and to determine relative age of fault-related anticlines. The Tiehchen, Tatu and Pakua ridge belt is a fault-related anticline system located in the hanging wall of the Changhua fault along the western thrust front of the foothills. Geomorphic systems are analysed with intent to detect the various responses of landforms and drainage pattern to late Quaternary deformation. Topography and drainage basin register uplift and are valuable tools to discriminate lateral propagation of an active frontal fold. Geomorphic field evidence and quantitative morphometric parameters are used to define the evolution of the rising anticline ridges and to infer tectonism style along an active front. Geometry of alluvial fans, formed along the frontal side of the anticlines, and weathered terrace deposits provide relevant information on neotectonics. Knowledge concerning these younger anticline ridges, makes this area a good example of an actively forming mountain front. We discuss in detail the origin of N045°, N095 and N120° trending oblique fault scarps which delimite numerous fault blocks. The fault scarps morphology is characterized by imbricate talus facets. Steeper topography accompanied by breaks in the slope along some transverse profiles, seems to correspond to the traces of successive uplifts. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Morphologic expression of Quaternary deformation in the northwestern foothills of the Ysyk-Köl basin,Tien Shan

The Tien Shan is one of the most active intracontinental mountain belts exhibiting numerous examples of Quaternary fault-related folding. To provide insight into the deformation of the Quaternary intermontane basins, the territory of the northwestern Ysyk-Köl region, where the growing Ak-Teke Anticline divided the piedmont apron of alluvial fans, is studied. It is shown that the Ak-Teke Hills are a sharply asymmetric anticline, which formed as a result of tectonic uplift and erosion related to motions along the South Ak-Teke Thrust Fault. The tectonic uplift gave rise to the local deviation of the drainage network in front of the northern limb of the fold. Optical (luminescent) dating suggests that the tectonic uplifting of the young anticline and the antecedent downcutting started 157 ka ago. The last upthrow of the high floodplain of the Toru-Aygyr River took place 1300 years ago. The structure of the South Ak-Teke Fault is examined by means of seismologic trenching and shallow seismic profiling across the fault. A laser tachymeter is applied to determine the vertical deformation of alluvial terraces in the Toru-Aygyr River valley at its intersection with the South Ak-Teke Fault. The rates of vertical deformation and an inferred number of strong earthquakes, which resulted in the upthrow of Quaternary river terraces of different ages, are calculated. The study territory is an example of changes in fluvial systems on growing folds in piedmont regions. As a result of shortening of the Earth’s crust in the mountainous belt owing to thrusting, new territories of previous sedimentation are involved in emergence. The tectonic activity migrates with time from the framing ridges toward the axial parts of intramontane basins.     

Hydrographic network as a marker of Quaternary tectonics: the example of El Mencha River from the Kaous region,Jijel, Algeria

A river can be an excellent marker of Quaternary tectonics. This method is applied to the El Mencha River case study (Jijel), which is an active region of Northern Algeria. In the Kaous locality (wilaya of Jijel), El Mencha River shows, at some points of its course, a difference in the banks’ altitude and a sinuosity that contrasts with the gentle slope. The right bank is in a high position with respect to the left bank. Bank uplift is emphasized notably by the staging of the stepped alluvial terraces. The oldest of these terraces is found about 6 m from the current level of the riverbed. On the left bank, the floodplain is very flared, with traces of abandoned or immature channels. Prospecting by electrical imaging has highlighted (i) superficial resistant unstratified and lenticular fluvial layers above conductive stratified deposits; (ii) an abnormal contact between the resistant and the conductive layers interpreted as a NE-SW fault zone, and (iii) the evidence of filled paleovalley which manifests as a V-shaped incision in stratified deposits. Channel pattern adjustment involving a lateral migration of the riverbed and the uplifted alluvial terraces are a consequence of the fault activity during the Quaternary period.     

西宁湟水河隐伏断裂发育模式探讨

近些年来一些地震表明,强震不仅发生在地表出露的活动断裂上,还发育在一些隐伏的未出露地表的构造上.大陆内部块体间的变形带不只是一条活动断裂,而是具有很大宽度的构造变形带,这已被大量的地震活动性资料所证实.因此,要正确评估地震危险性,就要研究构造带上地层变形的模型,而不仅是单条断裂的变形.湟水河隐伏断裂为一条隐伏在西宁市的断裂,位于西宁盆地中部,长12km,走向EW,浅层地震探测结果表明该断裂由两条正断层组成地堑式构造,横跨西宁地区的地层剖面研究结果指出湟水河隐伏断裂发育在宽缓背斜的核部,而宽缓的背斜和向斜由新近系红色泥岩组成.根据褶皱与断裂的关系认为,湟水河隐伏断裂为在北东向的区域主压应力作用下,褶皱变形过程中,在背斜的核部伴生形成的次级张性地堑式正断层.该褶皱及相关断裂发育在西宁盆地滑脱面之上,属于浅表性的断层,活动性不显著.     

Morphotectonic analysis of the Hazara arc region of the Himalayas, north Pakistan and northwest India

In the Hazara arc region of northern Pakistan, some of the active basements structures buried below a thick, detached sedimentary layer are inferred from the distribution of lineaments and the drainage patterns, as viewed in Landsat satellite imagery and from river profiles.A prominent set of NW-trending lineaments seen on satellite imagery, coincides approximately with the southwest or updip side of the Indus—Kohistan seismic zone (IKSZ) —the most active basement structure of the region, even though this structure is buried beneath and decoupled from a 12 km thick sedimentary layer. The IKSZ has been interpreted as an extension of the Himalayan Basement Thrust, and is also associated with a prominent topographic “step”.Knickpoints on major rivers in the region lie on or north of the IKSZ. All Indus River tributaries, examined north of the IKSZ, show prominent knickpoints, while two tributaries draining south of the IKSZ have no knickpoints. These results suggest ongoing uplift above and north of the IKSZ, and are consistent with the tectonic model obtained from the seismic data.Another prominent lineament set is detected along the north—south section of the Indus River. This set is probably related to the Indus River horst—anticline and associated reentrant.One of the two highest lineament concentrations occurs at the intersection between the NW-trending IKSZ lineament and the N-trending Indus River lineament. The other is along the west bank of the Indus Valley, 25 km north of Tarbela Dam.A topographic ridge (Swabi—Nowshera ridge) appears to be forming along the west side of the Indus River, in the Peshawar Basin. The rising ridge is ponding the Kabul River upstream of Nowshera, where the drainage is braided.     

Active deformation in the eastern Swiss Alps: post-glacial faults, seismicity and surface uplift

Post-glacial tectonic faults in the eastern Swiss Alps occur as single lineaments, clusters of faults or extensive fault zones consisting of several individual faults aligned along the same trend. The orientation of the faults reflects the underlying lithology and the pre-existing structures (joints, pervasive foliations) within these lithologies. Most post-glacially formed faults in the area around Chur, which undergoes active surface uplift of 1.6 mm/year, trend E–W and cut across Alpine and glacial features such as active screes and moraines. Additionally, there are NNW and ENE striking faults reactivating pervasive Alpine foliations and shear zones. Based on a comparison with the nodal planes of recent earthquakes, E–W striking faults are interpreted as active faults. Because of very short rupture lengths and mismatches of fault location with earthquake distribution, magnitude and abundance, the faults are considered to be secondary faults due to earthquake shaking, cumulative deformation in post- or interseismic periods or creep, and not primary earthquake-related faults. The maximum of recent surface uplift rates coincides with the youngest cooling of the rocks according to apatite fission-track data and is therefore a long-lived feature that extends well into pre-glacial times. Isostatic rebound owing to overthickened crust or to melting of glacial overburden cannot explain the observed surface uplift pattern. Rather, the faults, earthquakes and surface uplift patterns suggest that the Alps are deforming under active compression and that the Aar massif basement uplift is still active in response to ongoing collision.     

Morpho-hypsometric evolution of the Karuvannur River Basin,a tropical river in central Kerala,southwestern peninsular India

An integrated morphometric and hypsometric analysis coupled with asymmetric factor used as a proxy for the landscape evolution of the catchment of Karuvannur River. The present study area is a sixth order tropical river in the central Kerala which supplies water and sediments to the Vembanad-Kol Ramsar site. The Karuvannur River Basin (KRB) has been divided into six sub-watersheds (SW). Morphometric parameters (areal, linear, and relief) and hypsometric and asymmetric factors are measured for the delineation of morphotectonic evolution of the area. High values of drainage density, texture, ruggedness number, and hypsometric integral with relatively high volume of leftover rocks in the basin in SW-II and SW-III compared to the entire basin of KRB imply that these two sub-watersheds have been influenced by the tectonic activities. Further, detailed asymmetric data indicated that these two watersheds are tilted in opposite direction. It may be the result of reactivation of Precambrian fault/lineament in recent past. This has been supported by recent tremors and neotectonic studies in Kerala. Moreover, detailed field evidence along with google imagery revealed that the entire basin is a part of regional anticline associated with PCSZ. Geomorphic response to disturbance will produce a sensible, recognizable response; it can be well studied in rivers through detailed study of their sensitivity or behavioral changes. Rivers have an enormous capacity to absorb perturbation and these types of studies are essential for identifying/measuring tectonic activities, sediment diffusion, surface runoff in a drainage basin, and as an important tool for target oriented micro watershed management.     

Tectonics induced switching of provenance during the Late Quaternary aggradation of the Indus River Valley,Ladakh, India

The Indus River flows through Ladakh, one of the driest and coldest places on earth, in a tectonically active domain. Fluvial, glaciofluvial, lacustrine and debris dominated sequences represent the Late Quaternary sedimentary record along the river course. Karakoram Fault, a major crustal scaled feature reported to be active during the Quaternary, is associated with the Indus River drainage. Linkages between a major, active fault and deposits formed during the activity period of the fault are explored using heavy mineral deduced provenance and Optically Stimulated Luminescence(OSL) chronology.Five deposits in a ~200 km long stretch of the Indus River have been examined for a ~80 ka period to decipher the climate linked aggradation history. Damming of the Indus River at ~79 ka and existence of the Spituk Lake for >30 ka is demonstrated. Using geology of the provenance in relation to the mineralogical attributes of the Quaternary deposits, the major drainage reorganization when the connection of the Tangtse Valley to the Indus was blocked, is inferred at ~73 ka. It is supported by the geologicalgeomorphological evidence. The study demonstrates the application of provenance linked mineralogy in terrestrial aggradation in a tectonically active region.     

乌鲁木齐山前坳陷逆断裂-褶皱带及其形成机制

乌鲁木齐山前坳陷位于天山新生代再生造山带北侧,南以准噶尔南缘断裂与天山相隔,内部发育了几排逆断裂 背斜带,每一排构造带又由多个逆断裂 背斜组成。最南的齐古逆断裂 背斜带形成于中生代末,其北的玛纳斯逆断裂背斜带包含霍尔果斯、玛纳斯和吐谷鲁逆断裂背斜,形成于上新世末、早更新世初,受上、下２ 个滑脱面和断坡的控制,形成上、下２ 个背斜。再向北的独山子逆断裂背斜带由独山子、哈拉安德和安集海逆断裂背斜组成,形成于早、中更新世之间,主逆断裂向下在８ ～９ ｋｍ 深处的侏罗系中变为近水平滑脱面。此外,在独山子和吐谷鲁背斜的西北和东北还分别发育有正在形成之中的西湖和呼图壁隆起。研究了这些逆断裂 背斜带的地表和深部的构造特征、二维和三维几何学及运动学后指出,它们是在天山向准噶尔盆地扩展过程中发育于近水平滑脱面和不同断坡上的断展褶皱,独山子和安集海逆断裂 背斜的水平缩短量分别为２ ９００ ,１ ３５０ ｍ ,缩短速率分别为３９７ ,１８７ ｍ ｍ／ ａ。霍尔果斯、玛纳斯、吐谷鲁逆断裂 背斜的水平缩短量分别为５ ９００ ,６ ５００ ,６ ０００ ｍ ,相应的缩短速率分别为２０２,２２３ ,２０６ ｍ ｍ／ａ,准噶尔南缘断裂和乌鲁木齐山前坳陷第四纪?     

龙泉山断裂带断层最新活动年代及方式

龙泉山断裂带属龙门山前陆隆起,与青藏高原龙门山的隆升演化密切相关。为探讨龙泉山断裂带断层活动方式、期次及年代特征,在该断裂带不同部位采集了断层泥样品,通过扫描电镜(SEM)对样品中的石英颗粒进行了痕迹微形貌和溶蚀微形貌观察,通过电子自旋共振(ESR)测试了样品断层的最新活动年龄,并结合区域地震资料,进一步研究了龙泉山断裂带断层的发震潜力。结果表明: 龙泉山断裂带断层运动方式以黏滑为主,兼蠕滑; 具有多期次活动特征,强烈活动时间为早更新世—中更新世,晚更新世也有明显断层活动,全新世断层活动不明显; SEM 、ESR、热释光(TL)测得的断层最新活动年龄为(1 210±121)~(110±10.0) ka; 最新活动年代和活动性具有分段性,中段断层活动性较弱,北段和南段断层活动性较强。总之,龙泉山断裂带为1条活动性断裂带,具有一定的发震潜力,地震沿断裂带呈带状分布,但相比其西侧的龙门山断裂带,其活动性已大大降低。     

Latest active age and model of the faults in Longquanshan fault belt

Longquanshan fault belt belongs to Longmenshan foreland uplift, which is closely related to the uplift evolution of Longmenshan in Qinghai-Tibet Plateau. In order to explore the fault activity model, period and era characteristics of Longquanshan fault belt, some gouge samples were collected at different fault locations of Longquanshan fault belt. SEM was adopted for trace and dissolution micromorphology observation, and ESR was used to test the latest active age. Combined with the regional seismic data, further research on the seismic potential of Longquanshan fault belt was conducted. The results show that the main model of activity in Longquanshan fault belt is stick slip, with creep characteristics. The faults are characterized by multiple periods of activity. The strong acitivity era is the Early Pleistocene-Middle Pleistocene, there were obvious activities in the Late Pleistocene, and there weren’t any obvious activities in the Pliocene. The latest active ages measured by SEM, ESR, TL range from (1210±121) to (110±10.0) ka. The latest active age and activity is characterized with segmen tation, featured with weak activity in the middle segments and strong activity in the north and south segments. Longquanshan fault belt is an active fault belt with certain seismic potential. The earthquakes are distributed zonally along Longquanshan fault belt. However, its activity has been greatly reduced, compared with Longmenshan fault belt in the western part.     

英吉苏凹陷中─新生代背驮式前陆盆地构造特征及成因机制

英吉苏中新生代凹陷是在古生代逆冲推覆构造背景之上发育起来的背驮式前陆盆地。盆地的沉积作用和变形作用严格受基底参与的逆冲断层的控制。中新生代构造由北向南可划分七个带：北部斜坡带；群克─新开屏背斜带；英北向斜带；阿拉干背斜带；英南向斜带；古城墟斜坡带和罗布庄断凸带。叠瓦式逆冲断层、冲起构造、构造三角带、断展褶皱和披覆构造是英吉苏凹陷的主要变形样式。自三叠纪以来，不同时期的沉积中心自造山带向前陆方向迁移。 中新生界变形的动力学和运动学是与塔里木板块南缘活动大陆边缘的板块拼贴事件和壳内拆离缩短作用有关。     

塔里木盆地巴楚隆起北缘阿恰基底卷入构造

塔里木盆地巴楚隆起为第四系不整合覆盖的古隆起,在其西北缘发育NW走向的阿恰断裂、萨拉姆布拉克背斜、向斜和隐伏的乔来麦提断裂。地震剖面和钻井资料显示,阿恰断裂为倾向南的基底卷入逆冲断裂,向北逆冲,错断层位从前寒武系基底一直到中寒武统膏岩,从西向东逆冲断距减少。乔来麦提断裂则以中寒武统膏岩为滑动面,向南逆冲,并在断层端部发育萨拉姆布拉克断层扩展褶皱。这两种类型构造样式的断裂(基底卷入断裂和盖层滑脱断裂),在剖面上组成典型的楔形构造几何形态,平面上形成三角形构造。遥感影像解译指出阿恰断裂和萨拉姆布拉克向斜向北西方向延伸进入柯坪逆冲带,并在该带有相应方向的地表构造显现,与北东走向的柯坪逆冲带组成叠加构造。生长地层分析确定基底卷入构造形成于始新世—中新世,而柯坪逆冲带形成于第四纪,明显晚于巴楚隆起形成时代。     

Muglad盆地凯康坳陷生长断层活动定量分析及对油气成藏的控制

应用断层古滑距、滑动速率法研究苏丹Muglad盆地凯康坳陷生长断层活动,定量表征早白垩世、晚白垩世、古近纪-新近纪三幕构造旋回断陷期断层生长及活动强度的差异性。结果表明控凹断层为多期、多段式生长连锁模式;控构造带断层为初期生长连锁,后期简单生长模式;控圈闭断层表现为简单生长模式。早白垩世断陷期控凹断层分段生长影响烃源岩分布,断拗构造旋回造成砂泥岩沉积显著分异,形成下、中、上部多套储盖组合。油气的聚集层位及分布规律受圈闭类型、断层在Darfur群油气大规模运移期活动强度、Nayil组-Tendi组破坏期活动强度3方面因素控制,构造转换带横向背斜以及地垒型、反向断块型等古构造可形成早期残留油气藏或浅层次生油气藏,顺向断块不利于成藏。Darfur群与Nayil组-Tendi组滑移速率之比可以代表早期油气聚集与后期油藏破坏能力的相对大小,与单条断层伴生构造圈闭的油气纵向层位聚集状态有对应关系。凯康槽东侧为高产油气聚集带,隆起带以下组合白垩系成藏为主,断阶带上、中、下组合均能成藏;凯康槽西侧斜坡带和断阶带成藏条件差,隆起带北部成藏条件一般,多层系成藏但产量不高,隆起带南部成藏条件好于北部但以下组合白垩系成藏为主;坳陷带内断层晚期活动强烈,可形成次生油气藏。     

Fluvial response to active extension: evidence from 3D seismic data from the Frio Formation (Oligo-Miocene) of the Texas Gulf of Mexico Coast, USA

Tectonic deformation of the land surface is known to influence the gradient, water and sediment discharge and the grain-size of modern fluvial systems. Any change in these variables alters the equilibrium of a fluvial system, potentially causing a change in channel morphology. 3D seismic data from the Tertiary (Miocene) age, Upper Frio Formation, Kelsey Field, South Texas, in the US are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault (the Vicksburg Fault). The studied interval varies between 22 and 47 m thick, and spans several hundred thousand years. It consists of an alternation of fluvial sandstones, overbank mudstones and coal. Seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity. Prior to growth, a single sinuous channel is imaged. During growth, the fluvial system became decapitated by a developing rollover anticline, and a highly sinuous drainage network formed, with frequent avulsion events, headward propagation of streams and related stream capture. Increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline, more than 10 km from the active fault. More than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest. The increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems. The increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope.     

Cenozoic volcanism,tectonism and stream derangement in the Snowy Mountains and northern Monaro of New South Wales

Studies of Cenozoic lavas and associated sediments in the Kiandra‐Cabramurra and Adaminaby‐Cooma areas identify and date tectonic deformations responsible for differential uplift and drainage development of the region. Volcanic activity on the northern Monaro was mainly Eocene‐Oligocene but in the extreme north there are Early Miocene sediments and lavas. Volcanic activity and folding began to rearrange the drainage in the Eocene‐Oligocene. The headwaters of the Murrumbidgee River originally flowed south into the Eucumbene River but Early Miocene folding and faulting uplifted the Monaro Range and created a large lake near Adaminaby. Lake overtopping rerouted the drainage east and then south along the basalt‐filled valley of an old north‐flowing tributary, the ‘Adaminaby River’, forming the present‐day Murrumbidgee River. The folding also produced a 300 m height difference between the Berridale and Adaminaby Plateaus and formed a section of the Great Divide. This fold displacement ranks with the largest Cenozoic fault displacements. In the Kiandra area tectonism associated with Early Miocene volcanism rearranged the drainage and tilted the Kiandra area and Kosciuszko Block to the north.     

Late Neogene Mountain Building of Eastern Kunlun Orogen: Constrained by DEM Analysis

Topography, as a net result of the dynamic interaction between endogenesis and exogenesis, holds immense information on tectonic uplift, surface erosion and thus mountain building. The eastern Kunlun (昆仑) orogen, which experienced significant Late Neogene tectonic uplift and is located in an arid environment, is advantageous for morphotectonlc analysis based on well-preserved tectonic landforms. The digital elevation model (DEM) analysis was carried out for the central segment of the eastern Kunlun orogen based on shuttle radar topography mission (SRTM) data. River longitudinal profile analysis indicates that major rivers across the orogen are characterized by high river gradient indexes and intensive tectonic uplift. Differential uplift was also identified in swath-topography analysis in the studied area, which can be divided into three major tectonic-geomorphic units by orogenicstrike-parallel faults. It is indicated that the most active region is located to the south of the Xidatan (西大滩) fault with significant differential uplift. Another identified fault with differential uplift is the Middle Kuninn fault; however, the timing of which is suggested to be much older than that of the Xidatan fault. These analyses are eoneordantly supported by both field survey and studies of thermochronology, which in turn indicates that the DEM analysis bears great potential in morphotectonic analysis.     

滇西北弥渡地区主要断裂晚新生代发育特征及其动力学机制

弥渡地区位于滇西北断陷带东南缘,红河断裂带尾端与程海断裂交汇部位,是揭示滇西北断陷带形成机制及其与红河断裂带间运动学关系的关键区域。综合利用遥感解译及野外调查发现,区内主要发育有北东向的毛栗坡断裂,北西—北北西向的凤仪-定西岭断裂、弥渡断裂、密祉断裂、寅街断裂。对断裂错动地质、地貌体及擦痕的统计分析结果表明,毛栗坡断裂第四纪以左旋走滑活动为主兼具有正断分量;弧形的弥渡断裂及北西向的寅街断裂第四纪期间均以正断活动为主;上新世期间凤仪-定西岭断裂以右旋走滑为主,密祉断裂主要为伸展正断,二者第四纪期间均无明显活动。据弥渡地区主要断裂的几何形态、运动学特征及红河断裂带晚新生代活动性变化过程推测,控制弥渡盆地展布的弥渡断裂、寅街断裂等主要第四纪活动断裂是在继承和改造红河断裂带原有断层行迹的基础上形成的。上新世或更早,弥渡地区及滇西北断陷带的断裂活动与地壳张扭变形可能与红河断裂带尾端伸展变形作用有关,但第四纪期间,程海断裂基本上完全控制了弥渡地区主要活动断裂的发育,这一时期区内张扭变形的动力可能来自于川滇内弧带的顺时针旋转以及周缘南汀河断裂、畹町断裂与理塘断裂等左旋走滑断裂引起的区域性走滑拉分的共同作用。      

岷山隆起边界断裂构造活动初步研究

岷山隆起西以岷江断裂为界,东为虎牙断裂。该地区构造活动强烈,地震活动频繁,是重要活动区。岷山隆起是岷江断裂和虎牙断裂由西向东的推覆逆掩运动差异运动导致的。GPS及地质研究表明岷江断裂、虎牙断裂现今仍在活动。岷江断裂为左右旋走滑断裂,运动速度大于2mm／a;虎牙断裂整体速度2．55mm／a,断裂性质为右旋走滑断裂,而震源机制解为左旋走滑断裂。这一结果,可能与GPS观测时段、位置及断裂面结构、几何特征有关。