Holocene activities of the Taigu fault zone, Shanxi Province, and their relations with the 1303 Hongdong M=8 earthquake

The Taigu fault zone is one of the major 12 active boundary faults of the Shanxi fault-depression system, located on the eastern boundary of the Jinzhong basin. As the latest investigation indicated, the fault zone had dislocated gully terrace of the first order, forming fault-scarp in front of the loess mesa. It has been discovered in many places in ground surface and trenches that Holocene deposits were dislocated. The latest activity was the 1303 Hongdong earthquake M=8, the fault appeared as right-lateral strike-slip with normal faulting. During that earthquake, the Taigu fault together with the Mianshan western-side fault on the Lingshi upheaval and the Huoshan pediment fault on the eastern boundary of the Linfen basin was being active, forming a surface rupture belt of 160 km in length. Moreover, the Taigu fault were active in the mid-stage of Holocene and near 7 700 aB.P. From these we learnt that, in Shanxi fault-depression system, the run-through activity of two boundary faults of depression-basins might generate great earthquake with M=8.

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 Longmeushan thrust zone is not active, or at least its activity has been very weak since the Late Quaternary. Moreover, the total offset along the Xiaushuihe-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.

Holocene activities of the Taigu fault zone,Shanxi Province, and their relations with the 1303 Hongdong M=8 earthquake

No abstract available

Holocene activity evidence on the southeast boundary fault of Heqing basin, middle segment of Heqing-Eryuan fault zone, West Yunnan Province, China

The Heqing-Eryuan fault is an important part of the active fault system in the Northwestern Yunnan Province, China. Thus, the study on the nature, characteristics and activity history of this fault can provide not only the basis for seismic safety and engineering evaluation, but also the important information for the characteristics, history and patterns of the structural deformation of the southeastern margin of the Tibetan Plateau. Trench and faulted landforms investigations could provide effective paleoseismic methods to obtain the recent parameters of active faults. Using these methods, this study makes some breakthroughs on the recent activity of southeast boundary fault of the Heqing basin, middle segment of Heqing-Eryuan fault zone. Results indicate that the average vertical slip rate and left-lateral slip rate of the segment are about 0.28 mm/a and 1.8o mm/a respectively since the Late Pleistocene. The trench near the Beixi Village at the .outhea.t houndnrv fault of the lqaaing basinreveals that there have been at least three paleoearthquake events during the Holocene （8 ka BP）. The vertical displacement and sinistral strike-slip distance of a single paleoearthquake are ~20 cm and -1.2 m, respectively. The estimated paleoearthquake magnitudes with Ms7.o, and the recurrence interval at 2-5 ka, as well as the latest activity time during 800- 290 ca1 yr BP, are of great significance for preventing and mitigating regional earthquake disasters.

New Discovery of Holocene Activity along the Weixi-Qiaohou Fault in Southeastern Margin of the Tibetan Plateau and its Neotectonic Significance

Objective The lateral extrusion eastward of the Tibetan Plateau leads to the formation of the Sichuan–Yunnan block, which is the most representative active block in the southeastern margin of the Tibetan Plateau, characterized by strong and frequent seismicity(Li Ping et al., 1975; Zhang Peizhen et al., 2003; Li Yong et al., 2017). Its eastern boundary is composed of sinistral faults including the Xianshuihe, Xiaojiang faults, etc., and the western

Sinistral Strike-slip Movement Along Western Terminal Segment of the Active Daqingshan Piedmont Fault, Inner Mongolia, China

There are 18 gullies displaying sinistral contortions to different degrees along the western terminal segment about 10 km long of the active Daqingshan piedmont fault near the Donghe District, Baotou City. The contortion amount of gullies ranges from 20 m to 300 m. The contortion and length of the gullies are in direct proportion. The relation between piedmont terraces and gullies indicates that the gullies with upper reaches of about 1 ～ 5 km long and those smaller than one kilometer were formed at the end of Late Pleistocene and Holocene.Meanwhile, sandy gravel layer of alluvial-proluvial sediment on the upthrown wall is directly in contact with yellow clayey sand of the downthrown wall. During the Holocene, the sinistral strike-slip rate along the western terminal segment of the active Daqingshan piedmont fault reached 5 mm/a from age data of dislocated sediments. The evolutional mechanism of the active Daqingshan piedmont fault is also discussed in the paper.

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.

Characteristics of the Late Quaternary right-lateral strike-slip movement of Bolokenu-Aqikekuduk fault in northern Tianshan Mountains,NW China

The characteristics of the Bolokenu-Aqikekuduk（Bo-A） fault,a right-lateral strike-slip fault that runs for more than 700 km long and obliquely cuts North Tianshan Mountains,are evaluated here based on remote sensing data,and through an analysis of the results from field investigations as well as climate-geomorphic events. The fault is composed of a western segment with a NW strike and an eastern segment with a NWW strike.The western segment is nearly 250 km long,extending northwestward into Kazakhstan with a right-lateral strike-slip rate of 5 mm/a.This domain consists of 4-5 rupture sections,with 3-4 deformation belts,caused by ancient or historical earthquakes,and suggesting the potential for the occurrence of further strong earthquakes（with M≈7.5） in future. The eastern segment of the fault shows a right-lateral strike-slip rate of 1-1.4 mm/a,with the development of 3-4 deformation belts caused by ancient or historical earthquakes,and with a potential for future strong earthquake with M≈7.0. A typical strain partitioning style in the compression area has developed between the intermontane BoA fault and the piedmont thrust structures of Northern Tianshan Mountains,under the effect of oblique compression,as indicated by the piedmont thrust structure and the strike-slip fault in the mountains.

TECTONIC-GEOMORPHIC FEATURES OF THE STRIKE-SLIP FAULT ZONE IN EASTERN HUNAN AND WESTERN JIANGXI

Eastern Hunan-western Jiangxi, the main distribution domain of the Luoxiao MountainRange, is one of the key districts of the Circum-Pacific tectonically active belt in China, in whichNNE-trending en echelon strike-slip faulting since Cenozoic time has obviously controlled thefundamental framework of the modern land forms. Based on the study of tectonic evolution and ac-tive strike-slip faults, this paper discusses the forms, types and combinations of the modern tec-tonic land forms in this region.

Spatial Characteristics and Controlling Factors of the Strikeslip Fault Zones in the Northern Slope of Tazhong Uplift, Tarim Basin: Insight from 3D Seismic Data

The detailed characteristics of the Paleozoic strike-slip fault zones developed in the northern slope of Tazhong uplift are closely related to hydrocarbon explorations. In this study, five major strike-slip fault zones that cut through the Cambrian-Middle Devonian units are identified, by using 3D seismic data. Each of the strike-slip fault zones is characterized by two styles of deformation, namely deeper strike-slip faults and shallower en-echelon faults. By counting the reverse separation of the horizon along the deeper faults, activity intensity on the deeper strike-slip faults in the south is stronger than that on the northern ones. The angle between the strike of the shallower en-echelon normal faults and the principal displacement zone(PDZ) below them is likely to have a tendency to decrease slightly from the south to the north, which may indicate that activity intensity on the shallower southern en-echelon faults is stronger than that on the northern ones. Comparing the reverse separation along the deeper faults and the fault throw of the shallower faults, activity intensity of the Fault zone S1 is similar across different layers, while the activity intensity of the southern faults is larger than that of the northern ones. It is obvious that both the activity intensity of the same layer in different fault zones and different layers in the same fault zone have a macro characteristic in that the southern faults show stronger activity intensity than the northern ones. The Late Ordovician décollement layer developed in the Tazhong area and the peripheral tectonic events of the Tarim Basin have been considered two main factors in the differential deformation characteristics of the strike-slip fault zones in the northern slope of Tazhong uplift. They controlled the differences in the multi-level and multi-stage deformations of the strike-slip faults, respectively. In particular, peripheral tectonic events of the Tarim Basin were the dynamic source of the formatting and evolution of the strike-slip fault zones, and good candidates to accommodate the differential activity intensity of these faults.

The advance in obtaining fault slip rate of strike slip fault-A review

Slip rate along the major active fault is an important parameter in the quantitative study of active tectonics.It is the average rate of fault slip during a certain period of time,reflecting the rate of strain energy accumulation on the fault zone.It cannot only be directly applied to evaluate the activity of the fault,the probabilistic seismic hazard analysis,but also important basic data for the study of geodynamics.However,due to the nonstandardized process of obtaining fault slip rates for a given strike-slip fault,the results could be diverse based on various methods by different researchers.In this review,we analyzed the main advances in the approaches to obtain fault slip rate.We found that there are four main sources affecting the final results of slip rate:the displacement along the fault,the dating of the corresponding displacement,the fitting of the displacement and corresponding dating results,and paleoslip analysis.The main advances in obtaining fault slip rates are based on improving the reli-ability of the above four main factors.To obtain a more reasonable and reliable slip rate for a given fault,it is necessary to select a suitable method according to the specific situation.

天山内部那拉提断裂带全新世活动证据

天山山脉横跨欧亚板块,新构造时期强烈隆升。近年来已有研究表明,天山内部的那拉提断裂带东段全新世活动强烈。然而,针对那拉提断裂带其他段落的活动构造研究仍处于空白。文中选取特克斯段作为突破口,通过遥感解译、地质调查、无人机航测、探槽开挖和^(14)C测年,获得以下认识:1)那拉提断裂带特克斯段线性构造地貌特征清晰,可识别出断层崖、断层三角面、断层陡坎、鼓包、闸门脊、垭口、关门山、定向左旋错动的山脊和冲沟等断层地貌标志;2)基于无人机测图和LaDiCaoz半自动位错测量分析程序,获得水平最小位错量为3.4m;3)断裂发育于元古代和古生代地层中,探槽揭露了半山腰处的断塞塘沉积事件,剖面中至少记录了4次古地震事件;4)^(14)C测年结果显示,深约2m处样品的^(14)C测年结果约为(7.06±0.03)ka BP,最新一次形成的崩积楔的^(14)C测年结果约为(1.67±0.03)ka BP;5)利用OxCal年龄校正,在95.4%置信度下确定4次古地震事件的年龄范围:事件E1为2757BC—413AD、事件E2为3581—429BC、事件E3为4702—3932BC、事件E4为5742—5230BC。综上分析认为,全新世以来那拉提断裂带中段仍然活动强烈。

河西走廊西端文殊山南缘断裂新活动特征

文殊山南缘断裂为新发现的位于河西走廊西端嘉峪关—文殊山隆起带南侧的一条活动断裂,研究其活动特征对完善区域构造图像、认识地区地震危险性具有重要意义。文章根据遥感影像解译、野外地质调查、航空摄影测量,结合年代学测试,对断裂进行综合研究。结果表明,文殊山南缘断裂长约25 km,断裂总体走向为NW向,倾向NE。根据断错及未断错地貌测年,确定该断裂最新一次地震活动的时间在(0.8±0.1) ka与(1 887~1 725) cal a BP之间。利用高精度数字高程模型数据,获得断层陡坎高度,结合相应的地貌年代,估算断裂垂直滑动速率在0.2~0.25 mm/a。根据地震震级与破裂长度、位移量经验公式,估算文殊山南缘断裂潜在发震能力在6.8级左右,此震级下可能对邻近的乡镇、嘉峪关市区有较大的影响。

玉门断裂全新世活动特征及其与玉门地震的关系

玉门断裂是祁连山北缘断裂带的组成部分 ,也属于酒西盆地南缘断裂带的一支 ,是酒西盆地内二级构造单元的边界。玉门断裂表现为强烈的逆冲推覆特征 ,并有不大的左行水平位移分量 ,次级断裂走滑方向与其走向有关 ;玉门断裂自早更新世以来一直活动 ,是现代地震断裂 ,也是玉门地震的发震断裂。

青藏铁路唐古拉山—拉萨段全新世控震断裂研究

地表调查表明,沿青藏铁路唐古拉山—拉萨段存在5条重要的全新世控震断裂带,从北到南分别是温泉盆地西缘断裂带、安多盆地北缘断裂带、崩错断裂带、谷露西缘断裂带和当雄-羊八井断裂带。构造-地貌和年代学分析结果表明,北部的温泉盆地西缘断裂和安多盆地北缘断裂带的活动强度相对比较小,平均垂直活动速率约为0.2～0.5mm/a。南侧的谷露西缘断裂带和当雄-羊八井断裂带的全新世垂直活动速率为约(1.5±0.5)mm/a。而中部的崩错走滑断裂带的活动强度最大,晚第四纪期间的走滑速率可达(11±4.5)mm/a。全新世断裂活动和古地震研究表明,其中温泉盆地西缘断裂带、安多盆地北缘断裂带、崩错断裂带的西北分支、当雄-羊八井断裂带的当雄段等区域未来发生强震的概率相对更大。

郯庐断裂带江苏段安丘-莒县断裂全新世活动及其构造意义

郯庐断裂带是中国东部重要的活动断裂带和边界构造带,其鲁苏段全新世活动断层的空间展布和古地震序列是地学关注的焦点问题,也是准确评价区域地震危险性的重要参数.以往研究工作多集中在郯庐断裂带地表地貌现象明显且有强震记录的山东段,而江苏段则研究程度相对较低,有关郯庐断裂带江苏段全新世活动断层范围和古地震序列问题存在争议.本文利用野外地质地貌调查、浅层地震勘探、钻孔联合剖面以及古地震探槽等多层次综合方法,重点开展郯庐断裂带江苏段全新世活动断层的分布和古地震序列研究.结果显示全新世时期,安丘-莒县断裂是郯庐断裂带江苏段的主要活动断层,且江苏全段该断层都是全新世活动断层.通过对比宿迁闸-皂河镇断裂南北安丘-莒县断裂的断层地貌和断层最新活动时间,并结合宿迁闸-皂河镇断裂在第四纪没有活动过等证据,推测该断层在全新世时期并不是区域阻碍破裂的断层.探槽揭示郯庐断裂带江苏段全新世两次古地震事件,事件Ⅰ限定在(6.2±0.3)-(13.4±0.7)ka B.P.之间,而事件Ⅱ限定在(2.5±0.1)ka B.P.到现今,全新世两次古地震间隔较长.基于构造类比法,安丘-莒县断裂具有深部孕震的构造特点,是区域未来强震的潜在发震构造.

北天山西段库松木楔克山山前断层新活动特征初探

库松木楔克山山前断层是位于北天山西段再生造山带北缘一条重要的边界断层，是本次新发现和确定的一条活动断层。断层分为东、中、西三段：东段主要由4条断层斜列组合而成，单条断层长度为9～13km，在晚更新世～全新世仍在强烈活动，晚更新世以来的垂直错动量为3～4m，垂直活动速率为0．23～0．33mm／a，全新世以来的垂直错动量为0．5～0．8m；中段断层活动错断了中更新世至全新世地貌，形成多级断层陡坎和长约8～10km的地震形变带，晚更新世以来垂直活动速率为0．5mm／a；西段自晚更新以来无活动显示。

东昆仑断裂带西大滩段全新世古地震研究

对东昆仑断裂带西大滩段进行了断错地貌填图和古地震探槽揭露，共揭露出6次古地震事件，它们的年龄分别为10302±651aB．P．，8650±500aB．P．，7160±506aB．P．，2830±170aB．P．，1985±121aB．P．和1540±92aB．P．；古地震重复间隔分别为1652±820a，1490±711a，4330±534a，845±209a和445±152a。研究发现，西大滩段全新世古地震活动具有丛集现象和重复间隔时间的分段性，第1丛集期在10300—7100aB．P．期间，平均重复间隔1571±543a，第2丛集期在2800—1500aB．P．期间，重复间隔400—800a左右，平均重复间隔645±129a，两个丛集期间隔4300a。西大滩段全新世地震活动规律对昆仑山地区未来地震危险性评估具有重要意义。

红河断裂带南段全新世地震活动证据

有历史记录以来,红河断裂带北段曾发生包括1652年弥渡7级地震和1925年大理7级地震在内的6.0级以上地震9次。然而,红河断裂中、南段自公元886年有历史地震记录以来,没有1次6.0级以上地震记录。红河断裂带作为边界断裂是在废弃,未来不会有大地震发生,还是为长周期大地震的孕震构造?这个问题一直困绕着地质学界。通过室内高分辨率遥感影像的判读,并结合详细的野外地质、地貌调查,在红河断裂南段戛洒—腰街一带发现了一系列槽谷地貌,在十几km的地段都有显示;同时,组合探槽揭露的古地震信息及14C样品测年分析表明,红河断裂南段存在全新世期间地震活动的地质证据。

郯庐断裂带安徽紫阳山段发现全新世活动证据

安丘-莒县断裂(F_5)为郯庐断裂带中段东地堑内最新活动断裂。近年来,F_5江苏段研究成果丰硕,发现不同地段普遍存在全新世活动性,运动方式以右旋走滑兼挤压逆冲为主。以往研究未讨论过F_5在淮河以南安徽境内的延伸情况以及进一步的活动性问题。文中选取与F_5江苏段线性影像特征延伸一致的淮河南岸郯庐紫阳山段作为突破口,通过遥感影像解译、地质地貌调查和探槽开挖,初步得到以下认识:1)紫阳山段线性构造地貌特征清晰,断层发育于浮山至紫阳山一线的中生代红色砂岩隆起边缘缓坡,为安丘-莒县断裂(F_5)过淮河后的南延部分;2)朱刘探槽开挖揭示,该段错断了晚更新世晚期黏土层,晚更新世晚期—全新世早期黑色黏土层受断层活动影响沿断面灌入、填充,形成黑色断层条带及黑土充填楔,表明断层最新活动时代达全新世早期;3)朱刘探槽开挖揭示,该段第四纪以来存在至少3次古地震事件,第1次古地震事件推测年代为第四纪早、中期,第2次古地震事件年代为20.10~13.46ka BP,第3次古地震事件年代为(10.15±0.05)^(8.16±0.05)ka BP。上述研究成果弥补了对郯庐断裂带安徽段晚第四纪活动性认识的不足,为安徽省的地震监测和震害防御工作提供了基础数据。