Dating of the Karakorum Strike-slip Fault

This paper mainly discusses the timing of the Karakorum strike-slip fault, and gives a brief introduction of its structures, offset, and deformational style. This fault strikes NNW-SSE. Asymmetrical folds, stretching lineation, S-C fabrics, feldspar and quartz σ-porphyroclasts, domino structure, shear cleavages and faults in the fault zone are products of tectonic movements. They all indicate a dextral slip sense of faulting. Mylonitic bands are widely developed along this fault. Phengite appears, indicating rather high deformational pressure. Geochronological data indicate that the Karakorum strike-slip faulting occurred from 6.88±0.36 to 8.75±0.25 Ma. The cumulative displacement from Muztag Ata to Muji is about 135 km.     

Late Quaternary Slip Rate of the Xiugou Segment,Eastern Kunlun Fault Zone

The Eastern Kunlun fault zone (EKLF) is a large left-lateral strike-slip fault, whose slip rate is meaningful to seismic hazard assessment and geodynamics of the Tibetan Plateau. Previous studies suggested that the late Quaternary average slip rate was stable and uniform (10~13 mm/a) in the central and western segment of the EKLF. But there were a few researches of accurate slip rate in the central segment on the EKLF. Therefore, we focused on an offset and well preserved alluvial fan from Xiugou basin, located in the east of Xidatan-Dongdatan, to make it clear. Moreover, we used high-resolution satellite images and digital elevation model extracted from SPOT7 stereo image pairs to restore the offset alluvial fan, and combined terrestrial cosmogenic nuclides method, including 13 quartz-rich samples from this fan surface, 1 quartz-rich sample from the main active channel bed and 1 ¹⁰Be depth profile from this fan edge to eliminate the ¹⁰Be concentration of inheritance accurately, with 1 optically stimulated luminescence sample to obtain the reliable age of this alluvial fan together. Referring to field observations, this alluvial fan was offset left-laterally by (1 862±103) m, and its age is (76.55±3.20)~(106.37±3.38) ka which can be determined through the actual geologic setting and improving chi-square test. Thus, we used the Monte Carlo method to obtain a left-lateral slip rate of (20.3+3.5/-2.3) mm/a with 68% confidence envelopes since the late Pleistocene in the Xiugou basin. As a result, combining with the results of previous studies, the left-lateral slip rate indicated that the obviously decreasing activity transferred from late Pleistocene to Holocene on the central segment of the EKLF.     

青藏高原西部喀喇昆仑断裂活动构造研究进展综述（英文）

喀喇昆仑断裂系(KF)位于青藏高原西缘,具有右旋走滑性质,从帕米尔高原至尼泊尔西部延绵1 000多km。长期以来,对于喀喇昆仑断裂活动的起始时间、总位移量、在不同时间尺度上的滑移速率以及断层两端的精确位置等问题,都存在较大争议。为了更好的了解喀喇昆仑断裂现今的运动学特征及其与喜马拉雅—青藏高原陆内碰撞造山带的关系,确定喀喇昆仑断裂的滑移速率历史以及它随时间和/或空间的变化规律是极其重要的。目前研究表明,从现今的大地测量学尺度到几个百万年的地质学尺度,喀喇昆仑断裂走滑速率的变化范围为3～10 mm/yr。本论文对断裂各段的分布情况进行了详细描述,阐述了获得晚第四纪以来走滑速率的方法,回顾了喀喇昆仑断裂在大地测量学、晚第四纪以及地质学等不同时间尺度的走滑速率,并重点讨论了晚第四纪以来断裂的走滑速率。然后,确定了喀喇昆仑断裂北端的精确位置、讨论了其运动学意义和地震灾害效应。鉴于喀喇昆仑断裂具有长期的活动历史、规模巨大、运动速率较高,我们认为即使板块内部小尺度的似连续变形非常发育,板块模型依然可以很好的解释由于印度-亚洲板块碰撞造成的喜马拉雅北部的岩石圈变形。喀喇昆仑断裂、阿尔金断裂、昆仑断裂及龙木错—郭扎错断裂等青藏高原周缘的主要走滑断裂对青藏高原向东的挤出起着重要的调节作用。     

青藏高原西部喀喇昆仑断裂活动构造研究进展综述

喀喇昆仑断裂系(KF)位于青藏高原西缘,具有右旋走滑性质,从帕米尔高原至尼泊尔西部延绵1000多km.长期以来,对于喀喇昆仑断裂活动的起始时间、总位移量、在不同时间尺度上的滑移速率以及断层两端的精确位置等问题,都存在较大争议.为了更好的了解喀喇昆仑断裂现今的运动学特征及其与喜马拉雅—青藏高原陆内碰撞造山带的关系,确定喀喇昆仑断裂的滑移速率历史以及它随时间和/或空间的变化规律是极其重要的.目前研究表明,从现今的大地测量学尺度到几个百万年的地质学尺度,喀喇昆仑断裂走滑速率的变化范围为3~10 mm/yr.本论文对断裂各段的分布情况进行了详细描述,阐述了获得晚第四纪以来走滑速率的方法,回顾了喀喇昆仑断裂在大地测量学、晚第四纪以及地质学等不同时间尺度的走滑速率,并重点讨论了晚第四纪以来断裂的走滑速率.然后,确定了喀喇昆仑断裂北端的精确位置、讨论了其运动学意义和地震灾害效应.鉴于喀喇昆仑断裂具有长期的活动历史、规模巨大、运动速率较高,我们认为即使板块内部小尺度的似连续变形非常发育,板块模型依然可以很好的解释由于印度-亚洲板块碰撞造成的喜马拉雅北部的岩石圈变形.喀喇昆仑断裂、阿尔金断裂、昆仑断裂及龙木错—郭扎错断裂等青藏高原周缘的主要走滑断裂对青藏高原向东的挤出起着重要的调节作用.     

喀喇昆仑断裂北段晚第四纪活动特征及其构造意义

右旋走滑的喀喇昆仑断裂(KK F)作为青藏高原的西部边界, 在印度板块与欧亚板块碰撞引起的陆内变形过程中扮演了重要的角色。近年来KK F北段全新世以来的活动特征存在争议。通过遥感解译和野外观测, 在喀喇昆仑断裂(KK F)的北段——新疆卡拉苏地区, 对KK F及其两条分支断裂的几何学、运动学进行了研究, 获得了现今发育的冰水扇被右旋错断和冰水扇上分布羽列式T张破裂等指示KK F右旋走滑的证据。采集了KK F控制的浅冰水湖相沉积中贝壳的AMS 14C样品, 获得年龄分别为(5.20±0.03) ka、(5.61±0.03) ka 和(9.95±0.04) ka。表明KK F北段晚全新世以来仍在活动, 其右旋走滑速率约为3.7 mm/a, 累计垂向滑移速率约为1.7 mm/a。据前人在KK F中部的研究成果, 推测KK F北段在卡拉苏地区由南东往北西右旋走滑速率有增大的趋势。     

AGE OF THE ALTYN TAGH STRIKE—SLIP FAULT

AGE OF THE ALTYN TAGH STRIKE—SLIP FAULT     

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.     

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.     

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.     

Unraveling rift margin evolution and escarpment development ages along the Dead Sea fault using cosmogenic burial ages

The Dead Sea fault (DSF) is one of the most active plate boundaries in the world. Understanding the Quaternary history and sediments of the DSF requires investigation into the Neogene development of this plate boundary. DSF lateral motion preceded significant extension and rift morphology by ~ 10 Ma. Sediments of the Sedom Formation, dated here between 5.0 ± 0.5 Ma and 6.2_− 2.1^+ inf Ma, yielded extremely low ¹⁰Be concentrations and ²⁶Al is absent. These reflect the antiquity of the sediments, deposited in the Sedom Lagoon, which evolved in a subdued landscape and was connected to the Mediterranean Sea. The base of the overlying Amora Formation, deposited in the terminal Amora Lake which developed under increasing relief that promoted escarpment incision, was dated at 3.3_− 0.8^+ 0.9 Ma. Burial ages of fluvial sediments within caves (3.4 ± 0.2 Ma and 3.6 ± 0.4 Ma) represent the timing of initial incision. Initial DSF topography coincides with the earliest Red Sea MORB's and the East Anatolian fault initiation. These suggest a change in the relative Arabian–African plate motion. This change introduced the rifting component to the DSF followed by a significant subsidence, margin uplift, and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today.     

Holocene rockfalls in the southern Negev Desert,Israel and their relation to Dead Sea fault earthquakes

Rockfall ages in tectonically active regions provide information regarding frequency and magnitude of earthquakes. In the hyper-arid environment of the Dead Sea fault (DSF), southern Israel, rockfalls are most probably triggered by earthquakes. We dated rockfalls along the western margin of the DSF using terrestrial cosmogenic nuclides (TCN). At each rockfall site, samples were collected from simultaneously exposed conjugate boulders and cliff surfaces. Such conjugate samples initially had identical pre-fall (“inherited”) TCN concentrations. After boulder detachment, these surfaces were dosed by different production rates due to differences in post-fall shielding and geometry. However, in our study area, pre-rockfall inheritance and post-rockfall production rates of TCN cannot be evaluated. Therefore, we developed a numerical approach and demonstrated a way to overcome the above-mentioned problems. This approach can be applied in other settings where rockfalls cannot be dated by simple exposure dating. Results suggest rockfall ages between 3.6 ± 0.8 and 4.7 ± 0.7 ka. OSL ages of sediment accumulated behind the boulders range between 0.6 ± 0.1 and 3.4 ± 1.4 ka and support the TCN results. Our ages agree with dated earthquakes determined in paleoseismic studies along the entire length of the DSF and support the observation of intensive earthquake activity around 4–5 ka.     

Slip Rate of Yema River–Daxue Mountain Fault since the Late Pleistocene and Its Implications on the Deformation of the Northeastern Margin of the Tibetan Plateau

The slip rate of Yema River–Daxue Mountain fault in the western segment of Qilian Mountains was determined by the dated offset of river risers or gullies. Results indicate that the left-lateral fault slip rate is 2.82 ± 0.20 mm/a at Dazangdele site,2.00 ± 0.24 mm/a at Shibandun site,and 0.50 ± 0.36 and 2.80 ± 0.33 mm/a at two sites in Zhazihu. The ideal average slip rate of the whole fault is 2.81 ± 0.32 mm/a. The lower slip rate confirms part of the displacement of Altyn Tagh fault was transformed into an uplifting of the strap mountains in the western segment of Qilian Mountains,whereas another part transformed into sinistral displacement of Haiyuan fault. This study illustrates that the slip of large strike-slip faults in the northeastern margin of the plateau transforms into crust thickening at the tip of the fault without large-scale propagation to the outer parts of the plateau.     

一种断层影响基岩滑坡的失稳机理和稳定性分析

以某高速公路基岩滑坡为例．阐述了压性断层影响型滑坡的工程地质特点．总结了此类滑坡的失稳机理和失稳过程,并对拟建工况下的滑坡稳定性进行了分析。对此类工程的勘察、设计具有一定的指导意义。     

Active fault traces along Bhuj Fault and Katrol Hill Fault, and trenching survey at Wandhay, Kachchh, Gujarat, India

Several new active fault traces were identified along Katrol Hill Fault (KHF). A new fault (named as Bhuj Fault, BF) that extends into the Bhuj Plain was also identified. These fault traces were identified based on satellite photo interpretation and field survey. Trenches were excavated to identify the paleoseismic events, pattern of faulting and the nature of deformation. New active fault traces were recognized about 1km north of the topographic boundary between the Katrol Hill and the plain area. The fault exposure along the left bank of Khari River with 10m wide shear zone in the Mesozoic rocks and showing displacement of the overlying Quaternary deposits is indicative of continued tectonic activity along the ancient fault. The E-W trending active fault traces along the KHF in the western part changes to NE-SW or ENE-WSW near Wandhay village. Trenching survey across a low scarp near Wandhay village reveals three major fault strands F1, F2, and F3. These fault strands displaced the older terrace deposits comprising Sand, Silt and Gravel units along with overlying younger deposits from units 1 to 5 made of gravel, sand and silt. Stratigraphic relationship indicates at least three large magnitude earthquakes along KHF during Late Holocene or recent historic past.     

The Dihedral Angle and Intersection Processes of a Conjugate Strike‐Slip Fault System in the Tarim Basin,NW China

Recent studies, focused on dihedral angles and intersection processes, have increased understandings of conjugate fault mechanisms. We present new 3-D seismic data and microstructural core analysis in a case study of a large conjugate strike-slip fault system from the intracratonic Tarim Basin, NW China. Within our study area, "X" type NE and NW trending faults occur within CambrianOrdovician carbonates. The dihedral angles of these conjugate faults have narrow ranges, 19° to 62° in the Cambrian and 26° to 51° in the Ordovician, and their modes are 42° and 44° respectively. These data are significantly different from the ～60° predicted by the Coulomb fracture criterion. It is concluded that:(1) The dihedral angles of the conjugate faults were not controlled by confining pressure, which was low and associated with shallow burial;(2) As dihedral angles were not controlled by pressure they can be used to determine the shortening direction during faulting;(3) Sequential slip may have played an important role in forming conjugate fault intersections;(4) The conjugate fault system of the Tarim basin initiated as rhombic joints; these subsequently developed into sequentially active "X" type conjugate faults; followed by preferential development of the NW-trending faults; then reactivation of the NE trending faults. This intact rhombic conjugate fault system presents new insights into mechanisms of dihedral angle development, with particular relevance to intracratonic basins.     

走滑断裂带三维地震特征增强处理与描述研究

走滑断裂带由于纵向断距小,超深层地震信号弱,常规叠前深度偏移地震资料难以满足超深层断裂带精细描述需求。为提高断裂带成像精度,指导走滑断裂带解释描述和评价部署,以顺北地区走滑断裂带发育区三维地震资料为例,建立了一套以提高地震资料品质的保真保幅优化处理、频谱恢复提高分辨率处理、频谱分解处理、频率域多尺度断裂检测等技术为主的走滑断裂带地震特征增强处理与描述技术,该技术组合有效拓宽了地震数据频带,提高了地震数据分辨率,使超深走滑断裂带成像精度更高,为超深走滑断裂带的精细解释、描述评价、三维雕刻提供了高品质资料基础。结合顺北地区前人研究成果,综合利用频谱恢复提高分辨率处理、频谱分解处理、频率域断裂检测数据,不同尺度断裂带特征及断储关系预测效果更好,为进一步评价断裂带和部署井位提供了技术支撑。     

Slip sense inversion on active strike-slip faults in southwest Japan and its implications for Cenozoic tectonic evolution

Analyses of deflected river channels, offset of basement rocks, and fault rock structures reveal that slip sense inversion occurred on major active strike-slip faults in southwest Japan such as the Yamasaki and Mitoke fault zones and the Median Tectonic Line (MTL). Along the Yamasaki and Mitoke fault zones, small-size rivers cutting shallowly mountain slopes and Quaternary terraces have been deflected sinistrally, whereas large-size rivers which deeply incised into the Mio-Pliocene elevated peneplains show no systematically sinistral offset or complicated hairpin-shaped deflection. When the sinistral offsets accumulated on the small-size rivers are restored, the large-size rivers show residual dextral deflections. This dextral offset sense is consistent with that recorded in the pre-Cenozoic basement rocks. S–C fabrics of fault gouge and breccia zone developed in the active fault zones show sinistral shear sense compatible with earthquake focal mechanisms, whereas those of the foliated cataclasite indicate a dextral shear sense. These observations show that the sinistral strike-slip shear fabrics were overprinted on dextral ones which formed during a previous deformation phase. Similar topographic and geologic features are observed along the MTL in the central-eastern part of the Kii Peninsula. Based on these geomorphological and geological data, we infer that the slip sense inversion occurred in the period between the late Tertiary and mid-Quaternary period. This strike-slip inversion might result from the plate rearrangement consequent to the mid-Miocene Japan Sea opening event. This multidisciplinary study gives insight into how active strike-slip fault might evolves with time.     

古构造应力场反演的理论与实践——基于断层滑动矢量分析

古构造应力场恢复是重建区域地质演化历史的重要手段之一。断层作为地壳浅表发育的脆性变形构造,为恢复古构造应力场提供了重要地质条件。关于利用断层滑动矢量反演古构造应力场,前人进行了长期探索。目前其相关理论基础、研究方法与实际应用均取得重要进展。在断层滑动矢量反演古构造应力场的理论方面,改进的安德森模式描述了在发育先存薄弱带的情况下断层形成与演化的规律,克服了安德森模式只适用于均匀变形域的理论局限性;在研究方法方面,突破了在沉积盆地内部变形相对单一的限制,在造山带前陆或者叠加褶皱区等复杂变形区有效地开展了相关研究,并通过断层相关褶皱与同褶皱变形的滑动矢量分析,厘定出同造山作用的古构造应力场。这一方法在大巴山造山带强变形区得到了有效应用,为探讨其构造演化提供了基础。