兰州马衔山北缘断裂带古地震初步研究

兰州马衔山北缘断裂带为一条全新世活动断裂 ,大致由 4条次级断裂段组成 .沿断裂带发现了多期古地震事件 ,其活动具有时空不均匀性 .其中东段的马衔山段可以确定 2次古地震事件 ,距今 5850± 50 0aB .P .,2 0 60± 42 0aB .P .,复发间隔约 380 0a ;震级 7～ 7.5级左右 .中段的七道梁段发现 2次古地震事件 ,距今 1 682 0± 80aB .P .,1 0 80 0± 1 40aB .P ..西段的雾宿山咸水沟段可以确定一次古地震事件 ,其年代为 1 2 45± 560aB .P .,结合史料考证结果 ,认为就是 1 1 2 5年兰州 7级地震 .从古地震活动年代及复发间隔分析 ,马衔山北缘断裂带未来的强震危险段应为东段的马衔山段和西段的雾宿山咸水沟段 .     

东昆仑断裂带东段玛曲断裂古地震初步研究

东昆仑活动断裂是青藏高原东北部一条重要的NWW向边界断裂。玛曲断裂位于东昆仑断裂带的最东段。本文通过3个古地震剖面揭示出东昆仑断裂东段玛曲断裂全新世共有4次古地震事件。最新一次古地震事件为距今(1730±50)～(1802±52)a,第二次古地震的时间为距今(3736±57)～(4641±60)a;第三次为距今(8590±70)a;第四次为距今(12200±1700)a。其中第一次和第二次古地震事件的时间较为可靠,两次古地震事件之间的复发间隔为2400a左右,由此认为东昆仑断裂带东段的古震事件之间的复发间隔为2400a左右,古地震的离逝时间为距今(1730±50)～(1802±52)a。     

皇城--双塔断裂冬青顶段古地震活动规律的初步研究

冬青顶断裂段位于甘肃古浪皇城-双塔断裂的东段,由南北两条向北东方向呈弧形突出的近于平行的断裂组成.北断裂为挤压特征的逆冲断层,全长约40km,南断裂为具张性特征的正断层,全长约34km,二者具有内在的成生联系.该断裂全新世以来有过明显的构造活动.通过沿断裂带的追踪考察,在冬青顶断裂段上,开挖了3个大型探槽,经综合对比发现该断裂近15 000a以来共发生过3次古地震事件和1次历史地震事件,其发生年代分别是:事件Ⅰ15 930±1160 a B.P.,事件Ⅱ9 460±700a B.P.,事件Ⅲ5 000±500a B.P.,事件Ⅳ应是1927年古浪8级大地震(为历史地震事件).这4次事件在时空分布上具有明显的准周期复发特征.     

祁连山北缘佛洞庙-红崖子断裂古地震特征初步研究

佛洞庙-红崖子断裂位于祁连山北缘断裂带中部,是祁连山与河西走廊之间的一条重要边界断裂,断裂全长约110km,总体走向北西西,该断裂为一条全新世活动的逆-左旋走滑断裂,断裂活动形成了一系列陡坎、断层崖以及冲沟和阶地左旋等断错地貌.本文通过3个探槽剖面对发生在该断裂上的古地震事件进行了分析,可确定地震事件2次,事件Ⅰ为历史地震,发生在距今400年前,为1609年红崖堡71/4级地震;事件Ⅱ的年代为距今（6.3±0.6）ka B.P.和（7.4±0.4）ka B.P.之间.同时结合前人的一些研究资料,对古地震的复发模式和间隔进行了初步讨论.     

南天山及塔里木北缘构造带西段地震构造研究

南天山及塔里木北缘构造带位于帕米尔地区东北侧,地震活动强烈。文中通过地质构造剖面、深部探测资料和地震震源机制解资料,综合研究了该区的地震构造模型。结果认为,该区的构造活动主要表现为天山地块逆冲于塔里木地块之上。天山构造系统包括迈丹断裂及其前缘推覆构造;塔里木构造系统包括深部的塔里木北缘断裂、基底共轭断层和浅部的推覆构造。塔里木北缘断裂是发育于塔里木地壳内部的高角度断裂,其形成原因在于塔里木和天山构造变形方向的差异。塔里木北缘断裂为研究区大地震的主要发震构造,天山推覆构造和塔里木基底断裂系统均具有不同性质的中强地震发震能力     

北天山地震构造特征──航空照片解译

通过对北天山地区1:5万航空照片的解译结果,编制了北天山地震构造图。从中可见北天山新构造活动显著,山前差异运动强烈,活断裂、活褶皱发育,地震频繁。山区因断裂活动产生的山间断陷盆地也是地震活动场所。在近南北向区域应力场作用下,产生的线性构造大体分3组:东西向逆冲断裂;北西、北东向右旋、左旋逆走滑断裂。沿这些断裂,山脊、水系错动,冲洪积扇变形,并分布历史地震、古地震遗迹,可见这些断裂活动性强,多为发震构造。地震常常发生在这些断裂的端点、拐点及两组以上断裂的交汇部位。     

云南龙蟠—乔后断裂剑川段古地震初步研究

通过遥感影像解译和详细的野外考察,发现龙蟠—乔后断裂带剑川段晚第四纪以来长期活动,横跨断裂的水系左旋断错量可分为40m、140m、550m、1040m四个等级。经详细考察后选择后菁拉分盆地开挖探槽。探槽揭示了两次M6.5古地震事件:一次发生在10010±40a B.P.之前;另一次发生在6130±40aB.P.和6320±40aB.P.之间。结合前人研究,分析得出剑川盆地全新世以来发生了3次M6.5的地震,发生时间分别为1751年、6230±130aB.P.和10737±468aB.P.,其重复间隔约为5300a。由于1751年剑川6级地震相对于前两次地震释放的能量偏小,而且其离逝时间较前一次要明显长一些,故本段的地震危险性仍值得关注。     

北天山中段微震活动检测及其活动性和孕震构造分析

北天山地震带地处中国大陆强震高发区, 孕震构造复杂, 近年来陆续发生了2016年呼图壁M_S6.2地震和2017年精河M_S6.6地震。 由于测震台网相对比较稀疏, 该区域微震监测能力较弱。 本文主要采用波形模板扫描法对北天山中段(43.5°N~44.5°N; 85°E~87.5°E)进行微震事件检测, 并反演精细的一维速度结构, 重新定位地震; 深入分析该区域的地震活动性和孕震构造特征。 经过微震检测, 得到该地区2014年1月至2018年9月期间57902个地震事件, 是原地震目录的10倍, 完备震级从1.2降至0.5。 结果显示, 北天山中段地震十分活跃, 主要分布在北天山山前霍尔果斯—玛纳斯—吐谷鲁背斜带南翼的浅部和南玛纳斯—齐古背斜带深部, 呼图壁地震震后地震活动性有增强的趋势。 研究期间沿背斜构造带走向地震分布不均, 霍尔果斯—玛纳斯—吐谷鲁背斜带西段地震活动多于东段, 南玛纳斯—齐古背斜带东段地震活动显著强于西段。 经过重定位, 发现研究区的地震事件主要发生在褶皱内部的“盲断层”上, 这些隐伏断裂与区域活动断裂和背斜构造共同组成的断层系孕育了北天山山前活跃的地震活动, 并可能成为未来强震的发震构造。     

昌马断裂带古地震活动特征的新认识

昌马断裂位于祁连山西段,是祁连山系列次级断裂与阿尔金断裂东段的重要构造转换断层之一,于1932年发生7.6级地震。位于昌马断裂中东段的臭水柳沟古地震探槽揭示了2次地震事件:一次为1932年昌马地震事件,另一次为(902±44)a B.P.以来发生的事件,这弥补了昌马断裂全新世晚期古地震事件缺失的现状。结合前人的研究结果可确定昌马断裂全新世至少发生7次古地震事件,推测地震复发间隔为1ka左右,部分事件未能揭示。通过探槽揭示的低角度断层、地层变形和部分断裂的地貌特征可知,受阿尔金断裂NEE向挤出的影响,昌马断裂部分段落表现出低角度的逆冲推覆活动,形成其特有的低角度走滑现象,以吸收阿尔金断裂东段的左旋位移。这也说明昌马断裂在承担阿尔金断裂与祁连山西段系列断层的构造转换中起着重要作用。     

鲁西地区苍山-尼山断裂活动习性及地震活动研究

在广泛搜集以往研究资料的基础上,运用野外地震地质考察、典型地质剖面和探槽剖面分析、系统取样等方法,研究了苍山-尼山断裂的活动性质、最新活动时代和古地震事件。研究表明：苍山-尼山断裂以左旋走滑运动为主兼有逆冲运动分量;其第四纪晚期以来的活动具有分段性,以甘霖为界,北西段为晚更新世晚期至全新世早期,南东段为晚更新世晚期;有确凿证据的古地震事件有2次,其发生时间分别是距今6.4万年左右（E1）和距今1.4万年左右（E2）;另据考证,公元前179年＂齐楚地震＂也发生在该断裂上。根据历史地震和现代地震的研究成果,分析认为该断裂未来具有发生6.5级左右地震的潜在危险。     

新疆博罗可努—阿齐克库都克断裂精河段古地震与最新活动时代研究

博罗可努—阿齐克库都克断裂是西天山北西向右旋走滑断裂系中最北端的一条活动断裂,其在中国境内延伸最长。本文在艾比湖西侧及精河县东南侧最新地表形变上开挖两条探槽,进行该断裂古地震的初步研究。根据活动性质差异和断裂截切关系将该断裂分为艾比湖段和精河以东段,在对沉积物光释光年代和地震关系分析的基础上,确定了此两段断裂的最新活动时代均为全新世,初步确定其古地震期次,最新地震事件距今3.7—4.86 ka之间;根据冲沟位错和洪积扇年代测定结果,确定精河以东段的活动速率大于4 mm/a;根据探槽错动至地表,及地表破裂带位置及长度,推测艾比湖段可能为1765年精河M61/2的发震构造,且其震级很有可能被低估,因为艾比湖段的破裂总长度超过60 km,震级极有可能达到M7.0以上。     

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

Introduction The Taigu fault is located on the eastern boundary of the Jinzhong basin in the Shanxi fault depression system, which is one of the 12 major active basin boundary faults, and is also less studied among them. The reason for this is, firstly, the Jinzhong basin has no historical earth-quakes with M 7, while the two basins linked together in the northern and southern sides, the Linfen and Xinding basins all have had historical earthquakes with M 7; secondly, because the Jiaochen…     

Holocene activities of the Taigu fault zone,Shanxi Province,and their relations with the 1303 Hongdong <Emphasis Type="Italic">M</Emphasis>=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.     

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. Foundation item: Chinese Joint Seismological Science Foundation (201017). Contribution No. 2003A004, Institute of Crust Dynamics, China Earthquake Administration.     

山东泰安地区断层的最新活动与“泰山震

在卫星图像解译的基础上,对泰安地区５条主要断裂进行了野外地质地貌考察和年代学研究,发现泰山山前断裂为晚更新世晚期活动断裂,最新活动时代为距今（１．４２±０．１２）×１０４ａ。然后,讨论了发生在公元前１８３１年的“泰山震”的发震构造,认为“泰山震”可能与泰山山前断裂活动有关,可能是一次没有地表破裂、震级小于６．５级的中等强度地震     

天山地震带的地壳结构与强震构造环境

以中国西北地区的地震层析成像为基础,研究了天山地震带深部结构的基本特征．结果表明,天山地震带的地壳中部为低速的韧性滑脱层,南天山的断裂深度超过莫霍面,北天山的断裂深度一般只到地壳中部;天山莫霍面的深度一般大于５０ｋｍ,壳－幔边界由宽而缓的速度过渡带构成,中强地震主要位于盆山边界地壳中下部位波速变化较大的区域．帕米尔、南天山和塔里木之间存在一个北北东方向的低速带,乌恰和伽师地震分别位于该低速带东、西两侧的梯度带附近．推测帕米尔、南天山和塔里木之间的相对运动是导致低速带内部物质发生形变并在边界附近产生破裂的主要原因,地幔热物质的侵入对该地区的构造活动起到了重要的动力学作用．     

基于GPS观测的北天山主要断裂现今构造运动特征研究

借助分布在北天山地区最新GPS点位的运动观测资料, 利用GAMIT/GLOBK数据处理软件获取了北天山地区现今地壳的运动位移场． 以该位移场为基础, 利用弹性半空间位错理论, 估算了研究区内博罗科努—阿其克库杜克断裂和准噶尔盆地南缘断裂两条具有代表性的主要断裂的现今活动速率． 结果表明: 博罗科努—阿其克库杜克右旋走滑断裂东、 西两段滑移速率的差异性不明显, 1944年3月10日乌苏南M_S7.2强震发生后, 该断层现今表现为震后微蠕滑运动, 东、 西两段滑动速率均在1—2 mm/a之间; 准噶尔盆地南缘断裂现今滑动速率为(5.6±1.0) mm/a．      

Active faults and seismogenic models for the Urumqi city,Xinjiang Autonomous Region,China

We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of earthquake hazard in this area. Our work is based on an integrated analysis of data from investigations of active faults at the surface, deep seismic reflection soundings,seismic profiles from petroleum exploration, observations of temporal seismic stations, and the precise location of small earthquakes. We have made a comparative study of typical seismogenic structures in the frontal area of the North Tianshan Mountains, where Urumqi city is situated,and have revealed the primary features of the thrust-foldnappe structure there. We suggest that Urumqi city is comprised two zones of seismotectonics which are interpreted as thrust-nappe structures. The first is the thrust nappe of the North Tianshan Mountains in the west, consisting of the lower(root) thrust fault, middle detachment,and upper fold-uplift at the front. Faults active in the Pleistocene are present in the lower and upper parts of this structure, and the detachment in the middle spreads toward the north. In the future, M7 earthquakes may occur at the root thrust fault, while the seismic risk of frontal fold-uplift at the front will not exceed M6.5. The second structure is the western flank of the arc-like Bogda nappe in the east,which is also comprised a root thrust fault, middle detachment, and upper fold-uplift at the front, of which the nappe stretches toward the north; several active faults are also developed in it. The fault active in the Holocene is called the South Fukang fault. It is not in the urban area of Urumqi city. The other three faults are located in the urban area and were active in the late Pleistocene. In these cases,this section of the nappe structure near the city has an earthquake risk of M6.5–7. An earthquake M_S6.6, 60 km east to Urumqi city occurred along the structure in 1965.     

Seismotectonic Study on the West Part of the Interaction Zone Between Southern Tianshan and Northern Tarim

The interaction zone between southern Tianshan and northern Tarim is located at the northeast side of Pamir. It is a region with high seismicity. We constructed a seismotectonic model for the west part of this zone from geological profiles, deep crust seismic detection and earthquake focal mechanisms data. Based on the synthesized geological features, deep crust structure, and earthquake focal mechanisms, we think that the main regional tectonic feature is that the Tianshan tecto-lithostratigraphic unit overthrusts on the Tarim block. The Tianshan tectonic system includes the Maidan fault and thrust sheets in front of the fault; The Tarim tectonic system includes the underground northern Tarim margin fault, conjugate faults in basement and overthrust fault in shallow. The northern Tarim margin fault is a high angle fault deep in the Tarim crust, adjusting different trending deformation between Tianshan and Tarim. It is a major active fault that can generate large earthquakes. The other faults, such as the Tianshan overthrust system and the Tarim basement faults in this area may generate moderately strong earthquakes with different styles.     

北天山地区震源机制与构造应力场特征

本文利用新疆测震台网记录的宽频带波形数据,采用CAP方法反演北天山地区2010—2018年M_S≥3.0地震震源机制解,进一步结合早期研究区的震源机制数据反演了应力场。结果表明,研究区地震破裂类型以逆断型和走滑型为主,其次为正断型,过渡型最少; P轴方位大体与北天山地区主要断裂构造的走向垂直,研究区以中部和西部近NS向以及东部近NNE向的水平挤压作用为主;分区反演应力场显示研究区北部最大主应力轴σ₁方位由西到东呈NNW—NS—NNE渐变过程,研究区南部最大主应力轴σ₁方位自西向东先呈NS—NNE变化,再呈NNW—NS—NNE渐变;研究区R值普遍较大, R值较小的区域主要位于研究区的西部和东部,说明研究区东部和西部部分R值较小的地区向东西方向的扩展分量较小,主要表现为物质的隆升分量。