西秦岭临潭-宕昌断裂第四纪最新活动特征

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张波, 田勤俭, 王爱国, 李文巧, 徐岳仁, 高泽民. 西秦岭临潭-宕昌断裂第四纪最新活动特征[J]. 地震地质, 2021,43(1): 72-91.
ZHANG Bo, TIAN Qin-jian, WANG Ai-guo, LI Wen-qiao, XU Yue-ren, GAO Ze-min. STUDIES ON NEW ACTIVITY OF LINTAN-DANGCHANG FAULT, WEST QINLING[J]. SEISMOLOGY AND GEOLOGY, 2021,43(1): 72-91. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2021.01.005
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西秦岭临潭-宕昌断裂第四纪最新活动特征

张波^1),²⁾, 田勤俭³⁾, 王爱国²⁾, 李文巧^3),^*, 徐岳仁³⁾, 高泽民¹⁾

1)甘肃兰州地球物理国家野外科学观测研究站, 兰州 730000

2)中国地震局地质研究所, 北京 100029

3)中国地震局地震预测研究所, 北京 100036

*通讯作者: 李文巧, 男, 1978年生, 博士, 副研究员, 主要从事活动构造和地震工程研究, E-mail:lwq3278@163.com。

作者简介:张波, 男, 1986年生, 2020年于中国地震局地质研究所获构造地质学博士学位, 副研究员, 主要研究方向为新生代构造与活动构造, 电话: 13919015394, E-mail: kjwxn999@163.com。

收稿日期: 2020-01-09

基金项目: 中国地震局地震预测研究所基本科研业务专项(2018IESLZ02, 2017IES010101); 中国地震局地震科技星火计划项目(XH19045Y); 国家自然科学基金(41602225, 41802208)共同资助

摘要

临潭-宕昌断裂是西秦岭造山带内一条重要的分支断裂, 其最新活动特征是分析西秦岭构造变形的重要依据。临潭-宕昌断裂的新构造活动强烈, 中强地震频繁, 但目前对于断裂的新活动特征研究程度较低, 未见有其全新世活动地质地貌证据的报道。文中基于遥感解译、宏观地貌分析研究断裂的长期活动表现和分段性; 同时通过地质地貌考察、无人机摄影测量、差分GPS和放射性碳测年等方法定量研究断裂的新活动特征; 最后基于研究结果探讨了断裂及附近区域的地震危险性和区域构造变形。结果表明: 根据断层迹线收敛程度和宏观地貌差异, 可将临潭-宕昌断裂分为西、中、东3段; 断裂的运动性质以左旋走滑为主, 兼具逆冲分量, 左旋走滑使洮河及其支流、冲沟和山脊等发生同步左旋拐弯, 最大左旋位移可达3km, 逆冲分量使新近纪盆地边缘和内部形成300~500m的垂向位移; 断裂的最新活动时代为全新世, 限定了1次2090~7745aBP(置信度为2 σ)的全新世古地震事件; 全新世早期以来, 临潭-宕昌断裂东段主干断裂的左旋走滑速率为0.86~1.65mm/a, 垂直滑动速率为0.05~0.10mm/a。临潭-宕昌断裂分配了约2mm/a的左旋走滑分量, 是东昆仑-西秦岭阶区变形分配的关键断裂之一。

关键词: 临潭-宕昌断裂; 全新世活动; 滑动速率; 岷县-漳县 M_S6.6地震; 西秦岭

中图分类号:P315.2 文献标志码:A 文章编号:0253-4967(2021)01-0072-20

STUDIES ON NEW ACTIVITY OF LINTAN-DANGCHANG FAULT, WEST QINLING

ZHANG Bo^1),²⁾, TIAN Qin-jian³⁾, WANG Ai-guo²⁾, LI Wen-qiao³⁾, XU Yue-ren³⁾, GAO Ze-min¹⁾

1)Lanzhou National Observatory of Geophysics, Lanzhou 730000, China

2)Institute of Geology, China Earthquake Administration, Beijing 100029, China

3)Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China

Abstract

Located in the intervening zone between Tibetan plateau and surrounding blocks, the Lintan-Dangchang Fault(LDF)is characterized by north-protruding arc-shape, complex structures and intense fault activity. Quantitative studies on its new activity play a key role in searching the seismogenic mechanism, building regional tectonic model and understanding the tectonic interaction between Tibetan plateau and surrounding blocks. The LDF has strong neotectonic activities, and moderate-strong earthquakes occur frequently(three M6~7 earthquakes occurred in the past 500 years, including the July 22nd, 2013, Minxian-Zhangxian M_S6.6 earthquake), but the new activity of the fault is poorly known, the geological and geomorphological evidence of the Holocene activity has not been reported yet. Based on remote sensing interpretation and macro-landform analysis, this paper studies the long-term performance of LDF. Based on the study of fault activity, unmanned aircraft vehicle photogrammetry and differential GPS, radiocarbon dating, etc., the latest activity of LDF is quantitatively studied. Then the research results, historical strong earthquakes and small earthquake distribution are comprehensively analyzed for studying the seismogenic mechanism and constructing regional tectonic models. The results are as follows: Firstly, the fault geometry is complex and there are many branch faults. According to the convergence degree of the fault trace and the fault-controlled macroscopic topography, the LDF is divided into three segments: the west, the middle and the east. The west segment contains two fault branches(the south and the north)and the south Hezuo Fault. The south branch of the west segment mainly dominates the Jicang Neogene Basin, and the south Hezuo Fault controls the south boundary of Hezuo Basin. The middle segment has more convergent and stable trace, consisting of the main fault and south Hezuo Fault, and these faults separate the main planation surface of the Tibetan plateau and Lintan Basin surface geologically and geomorphologically. The fault traces in the east segment are sparsely distributed, and the terrain is characterized by hundreds of meters of uplifts. The branch faults include the main fault, Hetuo Fault, Muzhailing Fault and Bolinkou Fault, each controlling differential topography. Secondly, the motion property of the LDF is mainly left-lateral strike-slip, with a relative smaller portion of vertical slip. The left-lateral strike-slip offset the Taohe River and its tributaries, gullies and ridges synchronously, and the maximum left-lateral displacement of the tributary of Taohe River can reach 3km. Meanwhile, the pull-apart basins and push-up ridges associated with the left-lateral fault slip are also developed in the fault zone. The performance of vertical slip includes tilting of the main planation surface, vertical offsets of the boundary and interior of Neogene basin and hundred meter-scale differential topography. The vertical offset of the Neogene is 300~500m. Thirdly, one fault profile was newly discovered in Gongqia Village, revealing a complete sequence of pre-earthquake-coseismic-postseismic deposition, and this event was constrained by the radiocarbon ages of pre-earthquake and post-earthquake deposition. The event was constrained to be 2090~7745aBP(confidence 2 σ), which for the first time confirmed the Holocene activity of the fault. Fourthly, a gully with two terraces at least on the west side of Zhuangzi Village in the east segment of the main fault retains a typical faulted landform. The T2/T1 terrace riser of the gully has a left-handed dislocation of 6.3~11.8m, and the scarp height on terrace T2 is 0.4~0.7m, the radiocarbon age of the terrace T2 is7170~7310aBP, so the derived left-lateral strike-slip rate since the early Holocene in the east segment of the main fault is 0.86~1.65mm/a, and the vertical slip rate is 0.05~0.10mm/a. The derived slip rates are in line with the regional tectonic model proposed by the predecessors, so the LDF plays an important role in the internal deformation of the West Qinling. The clockwise rotation of the middle to east segments of the LDF acts as an obstacle to the left-lateral strike-slip motion, which inevitably leads to the redistribution and rapid release of stress, so earthquakes in the middle-east segment of the LDF are unusually frequent.

Keyword: Lintan-Dangchang Fault; Holocene activity; slip rate; Minxian-Zhangxian M_S6.6 earthquake; West Qinling

文章图片

0 引言

2013年7月22日岷县-漳县M_S6.6地震( 图 1)发生后, 开展的大量相关研究集中于震源特征(张元生等, 2013; 谭毅培等, 2015)、地震破坏与次生灾害(王兰民等, 2013; 许冲等, 2013; 郑文俊等, 2013a; Xu et al., 2014)、深部结构探测与发震构造分析(李翠芹等, 2013; 赵凌强等, 2015a, b)、震前异常分析(刘君等, 2013; 荣代潞等, 2013)等方面。这些研究深化了对该地震成因和区域构造模型的认识, 但关于发震构造的研究目前仍相对薄弱(何文贵等, 2013; 郑文俊等, 2013a, b)。

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图 1 松潘-西秦岭地区的地形地貌、活动构造与历史地震分布
底图为Shuttle Radar Topographic Mission(SRTM)数据, 分辨率为30m; 蓝色矩形框代表区域条带地形剖面; 黑色虚线框代表图 2 的范围; 震源机制解来源于GCMT目录^①(①http://www.globalcmt.org。)和USGS ^②(②https://neic.usgs.gov/neis/FM/。)。 F₁ 东昆仑断裂; F₂西秦岭北缘断裂; F₃龙门山断裂; F₄六盘山断裂; F₅塔藏断裂; F₆白龙江断裂; F₇光盖山-迭山断裂; F₈临潭-宕昌断裂; F₉哈南-青山湾-稻畦子断裂; F₁₀武都-康县断裂; F₁₁两当-江洛断裂; F₁₂礼县-罗家堡断裂; F₁₃龙日坝断裂; F₁₄岷江断裂; F₁₅虎牙断裂Fig. 1 Topography, active tectonics and historical earthquakes in Songpan-West Qinling area.

2013年岷县-漳县M_S6.6地震发生在临潭-宕昌断裂东段的一条分支断裂— — 禾驮断裂上, 该断裂在震后科考时被何文贵等(2013)发现并鉴定为晚更新世断裂, 岷县-漳县M_S6.6地震未断错地表。

除2013年岷县-漳县M_S6.6地震外, 临潭-宕昌断裂上还发生过1573年岷县6^3/4级地震、 1837年岷县6级地震等强震, 以及3次5~6级中强地震、 2次4.5~5级中等地震, 造成了严重的人员伤亡和灾害损失(顾功叙, 1983; 国家地震局震害防御司, 1995)。前人对上述地震开展过史料考证和发震构造研究, 由于受到强烈的自然侵蚀和人为改造的影响, 断错地貌难以保留, 针对发震构造的研究仍较薄弱(郑文俊等, 2005, 2007a, b; 何文贵等, 2006)。

尽管临潭-宕昌断裂被鉴定为晚更新世— 全新世断裂, 但缺乏其全新世活动的直接证据, 除个别露头或探槽的活动性鉴定工作外, 未精确限定断裂活动性定量参数。深入研究临潭-宕昌断裂的新活动特征, 有助于认识上述中强地震的发震构造和机理, 并进一步深化对西秦岭构造变形的理解。本文将介绍临潭-宕昌断裂新活动研究的一些新发现, 希望加深对临潭-宕昌断裂几何学、运动学特征和区域构造变形的认识。

1 区域地质背景

1.1 区域构造

晚新生代以来, 青藏高原周缘向NE扩展和挤出, 受到鄂尔多斯、阿拉善、四川盆地等坚硬地块的阻挡, 在高原边缘发生了复杂的构造变形(张培震等, 2006)。西秦岭位于松潘-西秦岭构造结的北部, 是上述多个块体相互作用最强烈和典型的地区之一。该地区发育了大量结构复杂、性质各异的活动断裂, 且大地震频发( 图 1)(袁道阳等, 2004; 郑文俊等, 2016)。西秦岭的南北边界断裂分别是东昆仑断裂和西秦岭北缘断裂, 2条边界断裂之间主要发育2组次级断裂系, 走向分别为NWW和NE, 在平面上呈 “ V” 形排列。较多研究认为, “ V” 形断裂系(尤其是NWW向断裂系)共同吸收和分配了2条边界断裂的差异运动(袁道阳等, 2004; 郑文俊等, 2016)。

1.2 临潭-宕昌断裂的研究现状

临潭-宕昌断裂是 “ V” 形断裂系中NWW向断裂系的一条重要分支, 其几何图像呈向N凸出的弧形, 在洮河以西走向为NWW, 在洮河一带走向顺时针旋转至NW, 并发散成4条分支断裂, 分别是主干断裂、禾驮断裂、木寨岭断裂和柏林口断裂。每条分支断裂的迹线也较复杂, 包含1条或多条分支( 图 2)(何文贵等, 2013)。

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图 2 临潭-宕昌断裂的几何展布与活动表现
小地震来自2009— 2019年中国地震台网统一地震目录 ^①(①http://www.csi.ac.cn/。)a 临潭-宕昌断裂带几何展布、小地震分布和历史地震; b 合作南断裂杯龙多村一带断层地貌; c 柏林口断裂棉柳滩一带的断层地貌; d 木寨岭断裂朱谷湾一带的断层地貌(照片来自何文贵等, 2013); e 禾驮断裂朱麻滩一带的断层地貌; f 朱麻滩断层剖面(照片来自郑文俊等, 2013b)Fig. 2 Geometric pattern and new activity of Lintan-Dangchang Fault.

前人对该断裂的新活动特征研究较少, 仅对局部点的活动性质和最新活动时代进行了鉴定(何文贵等, 2013; 郑文俊等, 2013b)。主干断裂上的贡恰村探槽揭露了2次晚更新世古地震, 时间约为(70.7± 7.4)kaBP和(12.0± 1.7)kaBP; 禾驮断裂是2013年岷县-漳县M_S6.6地震的发震断裂, 相当于冲沟三级阶地的砾石层被断错; 在木寨岭断裂上发现一次事件, 时间约为(65.6± 7.3)kaBP; 柏林口断裂错断了洮河三级阶地, 剖面上断层泥的热释光年龄为(81.9± 8.8)ka(何文贵等, 2013)。李光涛等(2019)认为临潭-宕昌断裂是以左旋走滑为主的晚第四纪活动断裂。上述研究主要反映了断裂的晚更新世活动, 关于全新世活动的证据较少。

本文在前人研究的基础上分析断裂的宏观地貌, 调查研究断裂的几何展布、新活动尤其是全新世活动特征, 并讨论断裂在西秦岭变形中的作用。

2 断裂的几何展布

在前人研究的基础上, 结合遥感解译和野外考察, 细化了临潭-宕昌断裂的断层迹线( 图 2)。根据断层迹线的收敛程度, 将临潭-宕昌断裂分为3段( 图 2)。西段为临潭-宕昌断裂的主断裂, 由南、北2支组成, 南支走向为NEE, 北支走向为NWW, 二者向E逐渐收敛。中段总体走向为NWW, 迹线收敛, 除主断裂的2条分支外, 还包括北侧的合作南断裂。合作南断裂的线性特征明显, 在杯龙多一带发育典型的断错地貌( 图2a, b); 主断裂南、北2支断裂近平行, 从贡恰以西向E延伸至洮河以西, 走向稳定, 迹线较清楚, 水系发生同步偏转。东段断裂呈帚状散开, 主要由主干断裂、禾驮断裂、木寨岭断裂和柏林口断裂组成(何文贵等, 2013)。主断裂位于最南侧, 走向NW, 与中段相比, 走向发生顺时针旋转, 断裂迹线总体不如中段清晰, 但庄子村一带发育5km长的线性地貌 ( 图 10); 禾驮断裂在2013年岷县-漳县M_S6.6地震极震区一带的断错地貌清晰( 图2e, f); 木寨岭断裂走向NWW, 与中段走向一致, 线性清晰, 差异地貌明显, 局部保留典型的断错地貌( 图2d); 柏林口断裂局部段线性清晰, 保留微地貌断错( 图2c)。

3 断裂的运动学特征

3.1 垂向运动特征

3.1.1 区域条带剖面

横跨西秦岭的条带剖面( 图 3)显示, 临潭-宕昌断裂(F₈)在洮河以西主要控制宏观地貌的转折, 最大、最小和平均高程曲线均在断裂位置发生突变, 地形起伏度也相应突变(P1); 洮河以东断裂的宏观地貌不如洮河以西显著, 断裂控制了局部的微弱隆起(P2)。

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	图 3 跨西秦岭NWW向断裂系的条带剖面红、黄、绿、蓝线分别代表最大、平均、最小高程和地形起伏度Fig. 3 Swath profiles across the NWW-trending faults in the West Qinling.

3.1.2 区域山脊点地形剖面

条带剖面虽克服了线剖面的局部性, 但受条带宽度、条带位置的影响较大。在较小范围内, 按一定步长提取的地形极值可能无法真实反映构造地貌, 因此, 我们借鉴王林等(2019)在喜马拉雅东构造结地区开展地貌分析所使用的方法, 即利用具有统计意义的区域内大量原始山脊点的条带剖面更真实、客观地反映构造地貌( 图 4, 5)。从分辨率12.5m的ALOS DEM提取山脊点, 具体步骤为: 首先提取不同级别流域的集水域, 然后将集水域矢量化, 删除与水系相交的山脊线, 将剩余的山脊线转换为山脊点, 之后为山脊点添加属性并转换为三维属性, 最后对区域山脊点进行三维剖面分析。

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	图 4 山脊点剖面分布Fig. 4 The ridge points and profiles.

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	图 5 山脊点剖面与宏观地貌红色虚线为深部断层, 绿色实线代表地貌面, 绿色虚线代表推测地貌面, 蓝色虚线框指示地形隆起区Fig. 5 Ridge points profiles and macro-topography.

山脊点剖面较好地显示了临潭-宕昌断裂的宏观构造地貌特征和分段差异( 图 5)。西段南支2条次级断层控制着新近纪盆地, 新近纪盆地高3400~3600m, 盆地两侧为海拔 $3^{}$ 800~ $4^{}$ 000m的高原夷平面( 图 5 中的P1)。中段主断裂控制了新近纪盆地, 分隔了新近系(临潭盆地)和主夷平面, 致使主夷平面发生掀斜, 前端翘起数百m, 盆地面与主夷平面前端的高差为300~500m( 图 4, 图 5 中的P2和P3)。主夷平面形成于20~3.6M $a^{}$ BP, 其上残留新近系沉积(潘保田等, 2002)。因此, 临潭盆地(新近纪盆地)和主夷平面的形成时代大致相同。在主夷平面抬升前, 二者可能位于同一高度, 现今的高差(300~500m)代表临潭-宕昌断裂的长期垂向位移。以主夷平面的形成年龄20~3.6Ma作为垂向位移(300~500m)的起始年龄, 估算得到临潭-宕昌断裂自新近纪以来的平均垂直滑动速率的下限为0.02~0.14mm/a。东段断裂控制着最高约400m的小隆起, 形成中间高且起伏大、两侧低且平缓的地形, 中间隆起区的起伏度约为300m; 东段帚状散开的分支断层分别控制局部差异地貌, 高程差一般为100~200m, 断裂延伸规模也远不如西段和中段( 图 5 中的P4和P5)。东段主干断裂控制的差异地貌为300~400m, 构成隆起区的南边界; 禾驮断裂两侧的高差约为200m; 木寨岭断裂和柏林口断裂控制隆起区北侧边界, 构成盆山边界。

3.1.3 垂向断错的地质地貌表现

在断裂中、东段过渡区, 主断裂断错至新近系内部, 新近系中发育一系列高100~200m的断层崖( 图 5 中的P6, 图6a)。一些年轻地貌体上也残留垂向断错地貌, 例如在贡恰村东15km处的山坡上形成了清晰的断层陡坎(34.817° N, 103.317° E)( 图6b, c)。

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	图 6 断裂的垂向运动表现(影像位置见图 2) a 新近系内部的垂向断错, 陡坎高度从ALOS DEM上测量; b 遥感影像上的线性特征; c 晚第四纪坡积物上发育的陡坎Fig. 6 Vertical offset expressions of the Lintan-Dangchang Fault(see Fig. 2 for image location).

综上所述, 临潭-宕昌断裂的垂向活动明显, 垂向断错(从老到新)表现为: 中、西段新近系和主夷平面之间存在落差(300~500m)、中段的主夷平面发生掀斜、东段的新近系被断错(100~200m); 第四纪以来的地形坡折和晚第四纪以来的地形陡坎。根据中段的垂向断错和主夷平面的形成年龄估算得到临潭-宕昌断裂长期垂直滑动速率的下限为0.02~0.14mm/a。

3.2 水平方向运动特征

临潭-宕昌断裂中段一系列发源于主夷平面、横穿主夷平面和临潭盆地面的洮河支流发生同步左旋, 左旋位移量为数百m— 约3km, 说明临潭-宕昌断裂具有显著的左旋分量( 图2a)。在西段和东段也可见水系同步左旋, 如东段主断裂、柏林口断裂以及西段的南、北分支断裂, 左旋位移量从几十m— 1km以上不等( 图2a)。除了跨断裂的水系左旋以外, 断裂沿线的小盆地、隆起等伴生构造也可能与断裂的左旋走滑相关。例如, 合作西南的旦尔道盆地正好位于断裂西段的左阶阶区( 图2a), 中、东段过渡区断裂右阶拐弯处的地形隆起( 图 5 中的P6)。

在王家坟一带山脊和冲沟发生同步左旋, 山脊的左旋量为116~252m(通过Google Earth测量)( 图7a)。甘霖沟一带山脊的最大左旋量达1146m, 1条冲沟的二级阶地左旋15~25m, 冲沟内发育3.6~4.0m高的裂点, 在冲沟一级阶地的基座中可见断层破碎带(左旋量通过Google Earth测量; 裂点高度由激光测距仪测量, 仪器型号为Leica Disto^TM D510)( 图7b— d)。庄子村一带山脊、冲沟及其阶地发生同步左旋( 图 10)。

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图 7 断裂左旋的地貌表现(位置见图 2)
a 王家坟北山脊和冲沟的同步左旋; b 甘霖沟一带山脊和冲沟的同步左旋; c 甘霖沟冲沟和二级阶地前缘的左旋位错, d 甘霖沟冲沟一级阶地的基座被断错并发育断层破碎带, 断层疑似错动一级阶地砾石层Fig. 7 Offset expressions related to left-lateral displacement of the Lintan-Dangchang Fault (see Fig. 2 for the locations).

综上所述, 临潭-宕昌断裂具有显著的左旋走滑特征。中段贯穿夷平面和新近系盆地面的洮河支流发生数百m— 约3km的同步偏转, 东段王家坟、甘霖沟一带山脊左旋数百m, 西段旦尔道一带的盆地和东段断裂拐弯处的地形隆起等现象反映了断裂新近纪— 第四纪以来的左旋性质; 冲沟和阶地发生数十m的同步左旋反映了断裂晚第四纪以来的左旋性质。新近纪— 早第四纪、晚第四纪的左旋位移均大于垂直位移。因此, 临潭-宕昌断裂自新近纪以来就开始活动, 活动以左旋走滑为主, 兼具倾滑性质。

3.3 全新世活动

在贡恰村一带, 临潭-宕昌断裂中段的影像线性特征清晰, 发育断层陡坎和断层沟槽等地貌( 图 8)。晚第四纪坡、洪积扇上的断层陡坎高1~4m(由差分GPS测量)( 图8b— d)。何文贵等(2013)在贡恰村西开挖了探槽, 揭示了断层的晚更新世活动。本文在前人探槽东侧约970m处(34.8493° N, 103.1516° E)开挖断面, 剖面上显示3套稳定沉积的地层(①、 ④、 ⑤)和2套与地震相关的快速堆积体(②、 ③)。揭露的地层( 图 9)包括:

① 黑色腐殖土, 内含3层较薄的红色砾石( 图 9 层①中的黄色虚线), 地层倾向S, 富含草根;

② 混杂堆积的浅红色砾石层, 无层理, 砾石分选性差, 磨圆度中等;

③ 倒三角形的充填楔, 为黑色腐殖土、浅红色砾石、暗灰色砾石和土的混杂堆积, 无层理, 含较多草根;

④ 灰黄色粉砂和黄土, 偶含草根;

⑤ 未胶结、弱分选和中等磨圆的砾石层。

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	图 8 贡恰村一带的断层地貌(位置见图 2) a 贡恰一带的卫星影像及山体阴影图, 山体阴影图由分辨率为0.15m的DEM生成; b 线性断层地貌; c 断层陡坎高(3.1± 0.6)m; d 断层陡坎高(1.14± 0.14)m。 P1— P4代表4条差分GPS剖面, 剖面位置见 8aFig. 8 Offset geomorphology in the west of Gongqia village(see Fig. 2 for the location).

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	图 9 贡恰村断层剖面Fig. 9 Fault outcrop in the west of Gongqia village.

2条断层(F_8-1 和F_8-2)控制张裂缝和裂缝中的混杂堆积体③和②, 至少指示了1次地震活动事件。 ③是地震发生前的地表黑色腐殖土, 在地震发生时与崩塌砾石混杂在一起堆积。 ②代表地震时的快速崩塌堆积, 堆积物杂乱, 分选差, 无层理, 应为崩积楔。 ①代表震后长期稳定的地表堆积。 ①— ③代表一次完整的地震旋回沉积, 即震前地表腐殖土— 地震崩塌— 震后稳定沉积的过程。根据①底部、 ④顶部的¹⁴C校正年龄( 图 9 和表1), 使用OxCal V4.3.2程序(Ramsey, 2017)校正得到该事件发生的时间区间(置信度为2σ )为(2090~7745)aBP。

表1 ¹⁴C样品的测年结果和校正年龄 Table1 Dating data and correction results of radiocarbon samples

需要注意的是, 该事件的年龄范围较为宽泛, 经分析可能的原因有2点: 1)地层④沉积后, 一段时间内没有沉积物在此堆积, 存在一定的沉积间断期。这种因素具有一定的可能性, 因为研究区所在的甘东南地区为构造活动强烈区, 地形抬升和河流下切形成了很高的地形起伏度, 侵蚀作用强, 沉积作用弱。 2)事件发生时, 地层④顶部的沉积物被侵蚀掉一部分, 或上盘较老的黄土在此堆积了一部分, 导致地层④的年龄偏大。我们更倾向于第2种原因, 即构造扰动导致地层年龄偏老, 从而导致事件的年龄范围较宽。另外, 上述2种原因都支持该事件年龄更接近于上部地层年龄。虽然事件的年龄范围较宽, 却不妨碍我们得到重要的结论之一, 即断裂存在全新世活动。

3.4 断层滑动速率

通过大量野外工作, 找到了一处相对理想的滑动速率测量点, 位于庄子村SW侧450m处。该点冲沟和2级阶地(T1, T2)发育同步左旋, 断错地貌保存相对完整, T2上残留断层陡坎( 图 10, 11)。

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	图 10 庄子村一带的断层地貌(位置见图 2) a 庄子村一带的线性断层地貌; b庄子村一带的地貌解译; c 清水沟的断错地貌; d 庄子村山脊断错和线性地貌Fig. 10 Offset expressions around Zhuangzi village(see Fig. 2 for the locations).

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	图 11 庄子村西的滑动速率点 a 断层断错冲沟和阶地; b 二级阶地的采样剖面Fig. 11 Slip rate site in the west of Zhuangzi village.

基于移动模型构建(Structure from Motion, SfM)(Westoby et al., 2012; Johnson et al., 2014)的无人机摄影测量技术可用于构建数字高程模型(DEM)。使用深圳大疆Inspire 1 V2.0无人机开展工作, 拍摄照片705张, 覆盖面积为0.195km², 飞行高度为40.2m。使用Agisoft Photoscan软件处理照片, 处理流程包括照片对齐、控制点校正、加密点云、建立网格和纹理, 最终生成5.92cm/像素的DEM。地形校正时使用12个控制点, 控制点数目符合艾明(2018)建议的最佳控制点个数; 地形控制点由Trimble Geoexplorer 6000 XH 后差分GPS进行测量, 仪器水平精度为2.5cm+1.2ppm, 垂直精度为4cm+1.5ppm。使用该仪器和方法在测量条件更恶劣的白龙江流域得到的DEM具有优于0.2m的点精度和0.16~0.33m的剖面精度, 完全满足高分辨率地貌测量的需要。利用DEM生成山体阴影图和地形等高线图, 用来解译断错地貌( 图12a, b)。根据Zielke等(2012)开发的Ladicaoz软件测量得到冲沟右岸T2阶地前缘的左旋位错为8.7~11.8m, T1阶地后缘的左旋位错为6.3~6.8m, 因此T2/T1阶地陡坎的左旋位错为6.3~11.8m。

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图 12 庄子村一带由无人机摄影测量获取的精细地貌和差分GPS剖面
a 由分辨率为6cm的DEM生成的山体阴影图, 黑色实线和箭头代表差分GPS剖面和剖面方向; b 地形等高线图, 等高距为0.5m, 黑色粗实线为较确定的阶地边界, 黑色虚线为不确定的阶地边界; c 差分GPS实测剖面; d 在DEM上提取相同位置的剖面Fig. 12 High-resolution DEM from unmanned aircraft vehicle photogrammetry and scarp profiles from differential GPS measurements.

同时, 通过后差分GPS实测得到的T2阶地上的断层陡坎高(0.55± 0.15)m, 在DEM上提取相同位置的陡坎剖面的高度为(0.64± 0.10)m, 两者接近( 图12c, d)。我们采用实测值(0.55± 0.15)m作为T2阶地上断层陡坎的高度。

限定T2阶地年龄的样品来自冲沟左岸人工清理的阶地剖面( 图 11)。该阶地剖面的下部为暗红色且风化半破碎的砾石层, 中部为薄层黄黏土, 厚约5cm, 上部为厚层黄土层, 含少量小砾石(最大砾径为3cm), 富含虫孔和草根。根据沉积特征可知, 上部黄土层应该是T2阶地废弃后的风成堆积, 且受到明显的生物扰动(植物草根、虫孔); 中部的薄层黄黏土可能代表冲沟内的淤泥堆积, 属于T2阶地被废弃之前的沉积。

样品测年结果和上述阶地剖面沉积分析吻合较好, 中部黄黏土层的¹⁴C校正年龄为7170~7310a, 而上部黄土层底部2个¹⁴C样品的校正年龄分别为315~500a和795~970a, 黄土底部的¹⁴C样品年龄明显不符合冲沟T2阶地的经验预期, 测试结果显著偏小(袁道阳等, 1999)。因此, 中部黄黏土层的¹⁴C年龄可以更好地代表冲沟T2阶地的形成年龄。

得到冲沟右岸T2/T1阶地陡坎的左旋位错(6.3~11.8m)和冲沟左岸T2阶地形成年龄( $7^{}$ 170~ $7^{}$ 310a)后, 基于邓起东等(2004)对滑动速率的定义, 计算得到左旋滑动速率为0.86~1.65mm/a。根据T2阶地陡坎高度(0.55± 0.15)m和T2阶地形成年龄, 计算得到垂直滑动速率为0.05~0.10mm/a。由此可知, 自全新世早期以来, 临潭-宕昌断裂主干断裂几乎为纯左旋走滑性质。

4 讨论

贡恰剖面的测年结果及庄子村断错地貌等现象证明临潭-宕昌断裂是全新世活动断裂。值得注意的是, 历史地震、中强地震和小地震集中发生在断裂东段, 而本文发现断裂的中、西段在距今 $2^{}$ 090~ $7^{}$ 745a间曾错断地表, 且甘南藏族自治州合作市、临潭县城位于断裂的中、西段附近, 因此, 临潭-宕昌断裂西段和中段的大地震危险性需要关注。

通过对不同时期地层地貌的水平和垂直位错开展分析, 发现自新近纪以来, 断裂的左旋走滑分量均大于倾滑分量, 断裂的活动性质以左旋走滑为主, 该结果与李光涛等(2019)的结论一致, 与袁道阳等(2004)、郑文俊等(2016)提出的区域构造模型相符。

临潭-宕昌断裂东段的主干断裂在全新世早期以来的左旋走滑速率为0.86~1.65mm/a, 垂直滑动速率为0.05~0.10mm/a; 虽然东段的其他3条分支断裂— — 禾驮断裂、木寨岭断裂和柏林口断裂的地质地貌表现( 图 2)和2013年岷县-漳县M_S6.6地震的震源机制(李晓峰等, 2013)均显示存在走滑分量, 但这些断裂仅为东段的分支, 规模相对较小, 左旋分量可能较小。因此, 临潭-宕昌断裂的左旋走滑速率可能略> 0.86~1.65mm/a, 与袁道阳等(2004)估算的2~2.5mm/a总体一致。综上所述, 临潭-宕昌断裂在西秦岭的变形分配中起到了重要作用, 与白龙江断裂、光盖山-迭山断裂等活动断裂共同分配了东昆仑断裂东段的左旋走滑分量, 实现了东昆仑-西秦岭阶区变形的协调匹配。

由东昆仑断裂、西秦岭北缘断裂、龙门山断裂等围陷的西秦岭次级块体, 其变形不仅发生在块体边界断裂上, 块体内部的弧形断裂系也发生相同量级的变形, 说明西秦岭的构造变形是跨区域、分布式的连续变形, 本文的研究结果倾向于支持连续变形理论(England et al., 1986)。

5 结论

本文通过断裂遥感解译、宏观地貌分析、断错地貌考察与测量、放射性碳测年等方法研究了东昆仑-西秦岭断裂阶区内的一条重要分支— — 临潭-宕昌断裂的新活动特征, 得到如下结论: 1)根据宏观地貌和几何特征, 可将断裂分为西、中、东3段; 2)断裂的运动性质以左旋走滑活动为主, 兼具倾滑分量; 3)全新世以来断裂曾断错至地表, 并发现1次发生于 $2^{}$ 090~ $7^{}$ 745 $a^{}$ BP的古地震事件; 4)临潭-宕昌断裂东段的主干断裂自全新世以来的左旋滑动速率为0.86~1.65mm/a, 垂直滑动速率为0.05~0.10mm/a。临潭-宕昌断裂在西秦岭的变形分配中起到了重要的作用。

致谢中国地震局地震预测研究所王林副研究员在地貌分析方面给予了帮助; 研究生王维桐和文亚猛在高分辨率地形数据采集方面提供了帮助; 审稿专家为本文提出了有价值的修改意见。在此一并表示感谢!

参考文献

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2018

0.0

... 地形校正时使用12个控制点, 控制点数目符合艾明(2018)建议的最佳控制点个数 ...

2004

0.0

... 8m)和冲沟左岸T2阶地形成年龄( 7170~ 7310a)后, 基于邓起东等(2004)对滑动速率的定义, 计算得到左旋滑动速率为0 ...

1983

0.0

... 5~5级中等地震, 造成了严重的人员伤亡和灾害损失(顾功叙, 1983 ...

1995

0.0

... 国家地震局震害防御司, 1995) ...

2013

0.0

何文贵, 郑文俊, 王爱国, 等. 2013. 临潭-宕昌断裂新活动特征与岷县漳县 M_S6. 6地震关系研究[J]. 地震工程学报, 35(4): 751—760.

Wen-gui

, ZHENG

Wen-jun

, WANG

Ai-guo

, et al. 2013. New activities of Lintan-Dangchang Fault and its relations to Minxian-Zhangxian M_S6. 6 earthquake[J]. China Earthquake Engineering Journal, 35(4): 751—760(in Chinese).

The Minxian-Zhangxian M6.6 earthquake,with a focal depth of 20 km,occurred at the boundary of Minxian and Zhangxian counties （34.5°N,104.2°E）,Dingxi city,Gansu Province,at 7：45 CST on July 22,2013.By 8：00 on July 29,1034 aftershocks occurred.Among them,nine above M3.0 include one M5.0～5.9,one M4.0～4.9,and seven M3.0～3.9 earthquakes.The strongest aftershock,which occurred at 9：12 on the date of the mainshock,attained MS5.6.Catastrophic damages caused by this earthquake are mainly attributed to poor residential structures erected by the government during a weak economy.The affected area was more than 10 000 km2 and involved in 6 cities and 13 counties ineluding Dingxi,Baiyin,Tianshui,Longnan,and Gannan Zang and Linxia Hui autonomous prefectures.Residents in Baoji,Hanzhong,Xianyang,Xi＇ an,Chengdu,and Mianyang felt this earthquake.The earthquake occurred at southeastern region of Gansu province,which is covered by very thick loess layer and exhibits complex topography such as steep,highly sloped mountains and crisscrossed ravines.It killed 95 people and injured 1 366.Secondary disasters caused by this earthquake include loess landslides,collapses,and pitfalls.Immediately following the earthquake,the China Earthquake Administration quickly organized field survey teams for seismicity monitoring,intensity studies,earthquake damage assessment,and scientific research,through which the first intensity distribution map of the Minxian-Zhangxian M6.6 earthquake was developed for conditions at 14：00 on July 24.The macroscopic epicenter of this earthquake,with an intensity of Ⅷ degrees,was located at Yongguang and Yongxing villages of Meichuan and Lalu Village of Hetuo.The long axes of intensity circled with an NW strike,in accordance with regional structures.This study discusses the basic parameters of this earthquake such as basic intensity distribution,damage features and seismogenic structure.This earthquake occurred at the eastern margin of the Qinghai-Tibetan Plateau at the intersection of the N-S seismic zone and the Kunlun-Qinling fault zone,which is the tectonic transformation zone between the NWW east-striking Kunlun fault and the northern margin of the western Qinling fault zone.We determined that the Hetuo fault,active since the late Pleistocene,passes through the extreme seismic area.Surface rupture phenomena such as landslides,ground fissures,earthquake pitfalls,sandblasting,and water oozing all exhibited zonal distribution along the Hetuo fault.The focal mechanism of this earthquake is consistent with the Hetuo fault.The strike of the nodal plane Ⅱ is 320° and 301.3°,as reported respectively by the Institute of Geophysics and the Institute of Geology,China Earthquake Administration,which also corresponds to the strike of the Hetuo fault.Moreover,the NE-dipping slip plane reported by the two agencies,51° and 57.3°,respectively,corresponds with the dipping direction of the Hetuo fault.Further,we determined that the Anjia Shan landslide slips laterally along a fault valley striking NW that resembles a long tongue with length and width of 310 m and 30～35 m,respectively.The plunge angel of fault striations on the slip plane is 12°～23°,and the main slip plane corresponds with the fault strike.Therefore,the Hetuo fault is seismogenic fault of the Minxian-Zhangxian M6.6 earthquake,which is a secondary fault,belongs to the Lintan-Tanchang fault zone.Three strong earthquakes above M6.0 have occurred near the epicenter of the Minxian-Zhangxian M6.6 earthquake on the Lintan fault,and two moderate earthquakes have occurred at this site in recent years,which include the Minxian M5.2 on November 13,2003,and the Minxian-Zhuoni M5.0 on September 7,2004.This earthquake represents the most recent activities of the Lintan-Tanchang fault zone.

2013年7月22日7时45分,在甘肃省定西市岷县和漳县交界（34.5°N,104.2°E）发生了一次MS6.6地震,震源深度20 km.截至7月29日8时,甘肃岷县、漳县MS6.6地震共记录到余震1 034次,其中3.0级以上余震9次,包括5.0～5.9级1次,4.0～4.9级1次,3.0～3.9级7次.其中最大余震为发生在7月22日9时12分的MS5.6地震.地震造成95人死亡,1 366人受伤.震区地处青藏高原与西秦岭陇南山地接壤区,黄土覆盖较厚,地形起伏较大,山坡陡峭,沟壑纵横,地震引发了黄土滑坡、崩塌和塌陷等次生灾害.另外,震区经济发展较为落后,房屋结构差,土木结构房屋所占比例较高,抗震性能差,是这破坏较重的主要原因.受灾范围涉及定西市、白银市、天水市、陇南市、甘南藏族自治州和临夏回族自治州等6个市（州）13个县,面积约1万多km2.甘肃天水、兰州、陇南、白银,陕西的宝鸡、汉中、咸阳、西安及四川成都、绵阳等地都有震感.地震发生后,中国地震局迅速组织地震现场考察队赶赴灾区,进行震情监测、烈度评定、震害损失评估和科学考察等工作,并于7月24日14时发布了甘肃岷县漳县6.6级地震烈度图.本次地震宏观震中位于岷县梅川镇永光、永星村和禾驮乡的拉路村一带,极震区烈度为Ⅷ度.烈度长轴走向为北西向,与区域构造线相一致.本文归纳总结了岷县、漳县MS6.6地震的基本参数、烈度分布、震害特征和发震构造背景等基本特征.本次地震发生在青藏高原东缘的甘东南地区,该区是南北地震带与昆仑山—秦岭断裂带等活动构造交汇部分部位,也是北西西向的东昆仑断裂与西秦岭北缘断裂之间的构造转换区.地震发生在靠近临潭—宕昌断裂一侧.通过野外地质调查,发现通过极震区有一条断层,即禾驮乡断层为活动断层,为晚更新世活动断层.包括滑坡、地裂缝、地震陷坑和喷沙冒水等地表破坏现象沿断层成带状分布.在震源机制解方面,且震源机制解也与该断层相吻合.中国地震局地球物理研究所给出节面Ⅱ走向为320°,与禾驮乡断层相一致.中国地震局地质研究所给出的是301.3°,也基本与其吻合.两个单位所给出的滑动面倾向为51°和57.3°,皆为向北东倾,与禾驮乡断层倾向也相一致.另外发现安家山滑坡长约310m,宽约30 ～ 35 m,沿断层谷地呈长舌形向北西做水平滑动,滑动面上擦痕侧俯角为12°～23°,主滑动面走向与断层走向相一致.说明禾驮乡断层为此次地震的发震断层,该断层属于区域上临潭—宕昌断裂的次级断层,该断裂历史上在本区内曾发生过3次6级以上强震,近期又发生过2003年11月13日岷县5.2级地震和2004年9月7日岷县—卓尼5.0级地震.此次地震是临潭—宕昌断裂进一步活动的结果.

... 这些研究深化了对该地震成因和区域构造模型的认识, 但关于发震构造的研究目前仍相对薄弱(何文贵等, 2013 ...

... 禾驮断裂上, 该断裂在震后科考时被何文贵等(2013)发现并鉴定为晚更新世断裂, 岷县-漳县M_S6 ...

... 每条分支断裂的迹线也较复杂, 包含1条或多条分支( 图 2)(何文贵等, 2013) ...

... 前人对该断裂的新活动特征研究较少, 仅对局部点的活动性质和最新活动时代进行了鉴定(何文贵等, 2013 ...

... 8)ka(何文贵等, 2013) ...

... 东段断裂呈帚状散开, 主要由主干断裂、禾驮断裂、木寨岭断裂和柏林口断裂组成(何文贵等, 2013) ...

... 何文贵等(2013)在贡恰村西开挖了探槽, 揭示了断层的晚更新世活动 ...

2006

0.0

... 何文贵等, 2006) ...

2013

0.0

李翠芹, 沈旭章. 2013. 岷县漳县 M_S6. 6地震震源区地壳速度结构特征初步研究[J]. 地震工程学报, 35(3): 448—454.

Cui-qin

, SHEN

Xu-zhang

. 2013. Characteristics of crustal structures in source area of the Minxian-Zhangxian M_S 6. 6 earthquake[J]. China Earthquake Engineering Journal, 35(3): 448—454(in Chinese).

An MS6.6 earthquake occurred at the junction of Minxian and Zhangxian on July 22,2013,at 7:45in the northern section of the North-South seismic zone in the southeast region of Gansu Province.This area is a moderate-strong earthquake-prone region in which the Minxian MS5.2 earthquake and Minxian-Zhuoni MS5.0 earthquake also occurred in 2003and 2004,respectively.In this study,we analyze teleseismic data recorded in 2008-2009 by Minxian station,which is the permanent station in closest proximity to the Minxian-Zhangxian earthquake.Receiver functions aligned by azimuth indicate obvious heterogeneity beneath the Minxian station;observed receiver functions of Minxian station vary according to azimuth.That is,receiver functions of the seismic source area and adjacent areas show obvious differences.In the seismic source area,the receiver function is clearly apositive signal of approximately 1.5s,which indicates that a high velocity zone is present in the middle-lower crust.In the adjacent areas,the receiver function is clearly a negative signal of approximately 1.5s,indicating the presence of a lower velocity zone in the middle-lower crust.This phenomenon shows obvious crustal structure differences between the seismic source area and adjacent areas.In addition,we used the H-kstacking method of receiver functions to determine the crustal thickness and wave velocity ratio of the two areas.The results show crust thicknesses of 45km and 47km and wave velocity ratios of 1.76and 1.69 in the source area and adjacent area,respectively.Therefore,obvious differences in crustal velocity structure appear between the two areas.In the seismic source area,the Ps,PpSs/PsPs clearly indicates crustal discontinuity.Therefore,the H-k stacking method of receiver functions was used to determine the depth of the discontinuity surface and the wave ratio velocity.The H-k stacking results showed an upper crustal thickness of 15km and a wave velocity ratio of 1.62.We estimated the middle-lower crustal thickness and wave velocity ratio to be 30km and 1.84,respectively.Therefore,the soft middle-lower crust is covered by the hard upper crust at the top in the source area.This type of small-scale material inhomogeneity may be an important part of the deep structure of the Minxian-Zhangxian earthquake background.We estimate that the rupture of the Minxian-Zhangxian earthquake may have been attributed to lower crustal flow leading to rupture of the upper crust.

利用距离2013年岷县漳县地震最近的固定台站岷县台2008-2009年的远震接收函数,确定了该地震震源区及临近区域的地壳厚度和波速比。结果表明:岷县台下方地壳速度结构的横向非均匀性较强,各方位接收函数差异较大,特别是震源区与临近区域存在明显的差别。临近区域的中下地壳存在明显的低速层,而震源区中下地壳中存在明显的高速区;且震源区地壳平均波速比为1.76,上地壳的波速比仅为1.62。据此推断:震源区是坚硬的上地壳覆盖在较软的中下地壳之上,岷县漳县地震破裂有可能是下地壳流的活动导致上地壳的破裂。

... , 2014)、深部结构探测与发震构造分析(李翠芹等, 2013 ...

2019

0.0

... 李光涛等(2019)认为临潭-宕昌断裂是以左旋走滑为主的晚第四纪活动断裂 ...

... 通过对不同时期地层地貌的水平和垂直位错开展分析, 发现自新近纪以来, 断裂的左旋走滑分量均大于倾滑分量, 断裂的活动性质以左旋走滑为主, 该结果与李光涛等(2019)的结论一致, 与袁道阳等(2004)、郑文俊等(2016)提出的区域构造模型相符 ...

2013

0.0

李晓峰, 裴惠娟, 徐辉, 等. 2013. 2013年7月22日岷县漳县6. 6级地震震源机制解[J]. 地震工程学报, 35(3): 459—462.

Xiao-feng

, PEI

Hui-juan

, XU

Hui

, et al. 2013. Focal mechanism of the Minxian-Zhangxian M_S6. 6 earthquake[J]. China Earthquake Engineering Journal, 35(3): 459—462(in Chinese).

The Chinese seismological station net determined that an MS6.6 earthquake occurred on July 22,2013,at 7:45CST at the border of Minxian and Zhangxian counties in Gansu Province. By the end of August 26,1300aftershocks had occurred in the seismic region of the main earthquake,including one of 5.0~5.9level,one of 4.0~4.9level,and nine of 3.0~3.9level.The largest,with magnitude of 5.6,occurred at 9:12on July 22.This earthquake caused heavy casualties and economic losses. In this study,the cut-and-paste(CAP) method was used to determine that the earthquake was thrust and strike-slip,MWwas 6.1,and the focal depth was 7km.The nodal plane II parameters of the best double-couple are strike 304°,dip 64°,and rake 44°.The strike of the nodal plane had the same trend as that of the Lintan-Tanchang fault,and the characteristic of dip and slip represent left lateral slip,which also corresponds to the Lintan-Tanchang fault.The nodal plane is representative of the seismogenic fault plane.Therefore,the Minxian-Zhangxian Ms6.6earthquake is in osculating correlation with activity of the Lintan-Tanchang fault.

利用甘肃"十五"数字地震台网的波形资料,采用CAP方法反演了2013年7月22日岷县漳县6.6级地震的震源机制解。结果显示:本次地震的震源性质为逆冲兼走滑型,矩震级MW6.1,震源矩心深度为7km。最佳双力偶节面Ⅱ走向304°,倾角64°,滑动角44°,其走向与附近的临潭-宕昌断裂的走向一致;倾角和滑动角,表现为左旋走滑的特性与临潭-宕昌断裂的性质相符合,判定该节面代表了主震的发震断层面。分析认为岷县漳县6.6级地震的发生与该断裂的活动密切相关。

... 6地震的震源机制(李晓峰等, 2013)均显示存在走滑分量, 但这些断裂仅为东段的分支, 规模相对较小, 左旋分量可能较小 ...

2013

0.0

刘君, 杜学彬, 范莹莹, 等. 2013. 甘肃岷县漳县 M_S6. 6地震前的地电阻率变化[J]. 地震工程学报, 35(4): 819—826.

LIU

Jun

, DU

Xue-bin

, FAN

Ying-ying

, et al. 2013. The geo-electrical resistivity anomaly before the Minxian-Zhangxian M_S6. 6 earthquake in Gansu[J]. China Earthquake Engineering Journal, 35(4): 819—826(in Chinese).

The MS6.6 earthquake occurred at the junction of Minxian County and Zhangxian County.The earthquake focal depth was 20 km.It was the largest event since the Shandan MS7.25 earthquake of 1954.The epicentral area was already known to be earthquake-prone,as there have been 25 earthquakes with magnitudes greater than five in recorded history within about 200 km of the epicenter.This earthquake occurred on the northeastern edge of the Qinghai-Tibet Plateau,which is formed by the subduction of the Indian plate in the north of China.Therefore,the earthquake was caused by the push from the Indian plate.The north-south seismic belt in which this earthquake happened has entered a new active period since May 12,2008,after the Wenchuan earthquake.The Wenchuan earthquake,the Yushu earthquake,and the Lushan earthquake show that its activity has not decreased.There are nine apparent resistivity stations within 400 km of from the epicenter.These are at Tongwei,Hanwang,Tianshui,Lanzhou,and Linxia in Gansu Province,Guyuan in the Ningxia Hui Autonomous Region,and Baoji,Zhouzhi,and Qianli in Shanxi Province.The Tianshui seismic station in Gansu uses the deep bore-hole technique,and the electrode depth is 100 m.This station is 156 km from the epicenter of the earthquake.This paper analyzed apparent resistivity observation data from these stations for 2002 to 2013 using the Fourier slide method and the normalized variation rate method.The Fourier slide method is used to exclude annual variation in geo-electrical resistivity observation data.The normalized variation rate method avoids the difficulties and arbitrariness of using human judgment to determine the abnormal changes in the base value.At the same time,this method retains the abnormal change patterns of the original curve.The results show,（1） for the geo-electrical resistivity anomaly phenomena before the earthquake,the relation between the abnormity and the earthquake is significant in time.The normalized variation rate method is better for the extraction of mid-term and short-term anomaly effects,and there were obvious abnormal changes.（2） The mediumterm anomalies mainly decreased,and the amplitude of the anomalies increased with distance from the epicenter.The Tongwei,Lanzhou,Tianshui,and Zhouzhi stations recorded sustained mediumterm anomalies for months or about a year.However,examination of the observation environment of the stations with abnormal changes showed that the recorded anomalies at some stations require further study.（3） Although the geo-electrical resistivity stations had environmental interference and other effects in the area surrounding the epicenter,abnormal changes in the geo-electrical resistivity were quite clear before the earthquake.There were large-amplitude seismic anomalies before the earthquake,as well as a decline in the main anomaly.Finally,we discussed the preliminary causes of the apparent resistivity anomalies.During the gestation of the earthquake,geo-electrical resistivity anomaly changes in the source area were associated with the accumulation of stress and ultimately result in progressive failure of rock.When the stress had accumulated up to the critical strength of the medium,micro-fractures started to form,this time because of the stress load in the later part of the preparation period.The accelerated change in this medium produced prominent geo-electrical resistivity anomalies.Decreasing anomalies are credible precursors in earthquake preparation processes.

应用富氏滑动、归一化变化月速率等方法处理了2013年7月22日甘肃岷县漳县Ms6.6地震震中400km范围内9个地电阻率观测台2002—2013年的观测资料,研究了本次地震前的地电阻率变化。结果显示,尽管震中周围的地电阻率台站存在环境干扰等影响,但在本次地震前地电阻率异常变化仍然很明显,表现出震前以下降为主、大幅度异常的特点。最后初步讨论了本次地震前地电阻率异常变化的可能成因。

... 赵凌强等, 2015a, b)、震前异常分析(刘君等, 2013 ...

2002

0.0

潘保田, 高红山, 李吉均. 2002. 关于夷平面的科学问题: 兼论青藏高原夷平面[J]. 地理科学, 22(5): 520—526.

PAN

Bao-tian

, GAO

Hong-shan

, LI

Ji-jun

. 2002. On problems of planation surface: A discussion on the planation surface in Qinghai-Xizang Plateau[J]. Scientia Geographica Sinica, 22(5): 520—526(in Chinese).

Planation surface is a remnant of landform in old age and the erosion surface is of a mature landform, according to the Davisian cycle. Studies on the long-term landscape evolution show that there are four types of planation surface, peneplain, pediplain, double leveling surfaces and cryoplain. The peneplain is formed through lowering of relief in wet region. The pediplain is developed by slope retreating in dry region. The double leveling surfaces appeares in Savanna landscape. The cryoplain is formed in periglacial environment. Measurement of erosion rates and retreating rates of slope indicated that formation of planation surface needs the tectonic equability for severl million years or thousands million years. In the the Qinghai-Xizang Plateau, there are two planation surfaces and one erosion surface, Summit Surface, Main Surface and Erosion Surface. The Summit Surface have formed in the Oligocene and early Miocene, and the Main Surface between 20-3.6Ma B.P. Tectonics on the Qinghai-Xizang Plateau were relatively stable between 3.6Ma B.P. and 1.7Ma B.P. and the Erosion Surfaces was formed. Because the Main Surface is a "jumping-off point" of the Qinghai-Xizang Plateau, studies on its mode of formation and height have great significance in determining the altitude of the Qinghai-Xizang Plateau before uplift. Synthesizing the proofs from mammal fauna, regolith and geomorphology, we think the Main Surface was developed as a typical double level surface. There could be the peneplain in the south of it and the pediplain on north. Its altitude should not exceed 1000 m when it was formed. The Intense tectonic uplift, which resulted in the present Qinghai-Xizang Plateau with an altitude of 4500-5000m, happened in last 3.6Ma when the Main Surface was destroyed.

MOE National Laboratory of Western China’s Environment & Department of Geography, Lanzhou University, Lanzhou, Gansu 730000

长期地貌演化研究表明,夷平面的形成有4种基本方式:准平原、山麓剥蚀平原、双层水平面和冻融剥夷平原。它们的形成都需要上千万年至数亿年的构造相对稳定时期。青藏高原上的层状地貌面可以划分为两级夷平面和一级剥蚀面。山顶面形成于渐新世至中新世早期;主夷平面是以双层水平面或山麓剥蚀平原形式发育的,大致形成于20～3.6 Ma B.P.期间,完成时的高度低于1000m;剥蚀面形成于3.6～1.7 Ma B.P.期间。

... 6M aBP, 其上残留新近系沉积(潘保田等, 2002) ...

2013

0.0

荣代潞, 李亚荣. 2013. 2013年7月22日岷县漳县6. 6级地震前地震相关长度增长现象[J]. 地震工程学报, 35(3): 455—458.

RONG

Dai-lu

, LI

Ya-rong

. 2013. Analysis of the growth phenomenon of seismic correlation length prior to Minxian-Zhangxian earthquake[J]. China Earthquake Engineering Journal, 35(3): 455—458(in Chinese).

The seismic correlation lengths prior to the Minxian-Zhangxian earthquake occurring on July 22,2013,have been studied using the single-link cluster analysis(SLC)method.The catalogs used were downloaded from the China Earthquake Data Center(CEDC;http://data.earthquake.cn/data/).Earthquakes that occurred during the five years prior to the main shock until its origin time were located in an area centered on the main shock(34.5N°,104.11°E)with a range of 32°~37°,102°~107°.We selected 2.5(ML)as the minimum magnitude and verified the completeness of the catalogs prior to the mainshock using the Gudengberg formula,which showed good results above magnitude ML=2.5.The result shows that an increase in correlationlength for moderate-sized earthquakes was observed nearly 1.5years before the main shock and can be fitted well by the power law.For the preparation and occurrence stage of the earthquake process characterized as a self-organized critical phenomenon,direct testing for the increase in spatial correlation lengths prior to large earthquakes is an independent approach used to detect critical point behavior in observed seismicity.The results of this study show that the self-organized critical point characteristic was been observed prior to the Minxian-Zhangxian MS6.6earthquake.The results from the many earthquake applied to systematically extract a region of increased correlation length from a dataset.Estimates for the epicenter of an expected mainshock may be then obtained from the results of the grid search.

利用单健群分析方法研究了2013年7月22日岷县漳县6.6级地震前地震空间相关长度增长现象。结果表明,从2011年下半年开始主震周围区域地震空间相关长度明显增长。利用这种特征对可能的大震危险区进行网格式搜索,至少可以对未来强震发生的地点进行初步预测。

... 荣代潞等, 2013)等方面 ...

2015

0.0

... 谭毅培等, 2015)、地震破坏与次生灾害(王兰民等, 2013 ...

2013

0.0

王兰民, 吴志坚. 2013. 岷县漳县6. 6级地震震害特征及其启示[J]. 地震工程学报, 35(3): 401—412.

WANG

Lan-min

, WU

Zhi-jian

. 2013. Earthquake damage characteristics of the Minxian-Zhangxian M_S6. 6 earthquake and its lessons[J]. China Earthquake Engineering Journal, 35(3): 401—412(in Chinese).

According to scientific investigation of the seismogenic structure,housing and the lifeline engineering damages and the secondary geological disasters induced by the Minxian-Zhangxian MS6.6 earthquake on July 22,2013,that the characteristics of seismogenic structure and seismic intensity distribution,damage characteristics and failure mechanism of houses in different intensity zones are introduced.Moreover,a thorough analysis of typical loess landslides are carried out,the damage characteristics of fault effects,amplification effects of mountain and slope effects are summarized as well.Based on the in-depth investigation of seismogenic structure,site conditions of the quake-hit areas,different houses damages and secondary geological disasters,some lessons have been proposed for reconstruction of the quake and seismic fortification in the future.

通过对2013年7月22日甘肃岷县漳县6.6级地震的发震构造、房屋和生命线工程震害、次生地质灾害的现场科学考察,系统介绍了本次地震发震构造、宏观地震烈度分布特征、不同烈度区房屋震害特点及破坏机制,并对地震中突出的黄土滑坡震害开展了深入的分析,进而总结归纳了此次地震中的断层效应、山体放大作用和边坡效应等震害特征。在此基础上提出了针对灾区灾后重建和今后我国的抗震设防工作的几点启示。

... 谭毅培等, 2015)、地震破坏与次生灾害(王兰民等, 2013 ...

2019

0.0

... 在较小范围内, 按一定步长提取的地形极值可能无法真实反映构造地貌, 因此, 我们借鉴王林等(2019)在喜马拉雅东构造结地区开展地貌分析所使用的方法, 即利用具有统计意义的区域内大量原始山脊点的条带剖面更真实、客观地反映构造地貌( 图 4, 5) ...

2013

0.0

许冲, 徐锡伟, 郑文俊, 等. 2013. 2013年甘肃岷县漳县6. 6级地震触发滑坡及其构造分析[J]. 地震地质, 35(3): 616—626. doi: 103969/j. issn. 0253-4967. 2013. 03. 015.

Chong

, XU

Xi-wei

, ZHENG

Wen-jun

, et al. 2013. Land slides triggered by the 2013 Minxian-Zhangxian, Gansu Province M_S6. 6 earthquake and its tectonic analyses[J]. Seismology and Geology, 35(3): 616—626(in Chinese).

On July 22,2013,an earthquake of M S 6.6 occurred at the boundary between Minxian County and Zhangxian County,Gansu Province of China. Many landslides were triggered by the earthquake and the landslides were of various types,mainly in falls,slides,and topples occurring on loess cliffs,and also including soil deep-seated coherent landslides,large-scale soil avalanches,and slopes with cracks. Most of the landslides were distributed in an elongated area of 250km 2 ,parallels to the Lintan-Dangchang Fault, with about 40km in length and the largest width of 8km. Landslides occurrence shows obvious difference along the central line of the elongated area,corresponding to different characteristics of different segments of the seismogenic fault. The elongated landslides main distribution area and the location of the epicenter indicate that the direction of the fault rupture propagation is from southeast-east to northwest-west. Finally,two probable reasons causing the horizontal distance of about 10km between the central line of the elongated area and the Lintan-Dangchang Fault are presented.

1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China

2013年7月22日,甘肃省岷县漳县交界发生了 M S 6.6地震。地震触发了大量的、类型各种各样的滑坡。滑坡类型以黄土崖崩、滑、倾为主,还有一些深层连贯型土质滑坡、大型土质流滑、斜坡裂缝等类型。地震滑坡主要分布在一个与临潭-宕昌断裂平行的长条形区域内。该长条形区域面积约为250km 2 ,长度约40km,最大宽度约8km。对应不同构造段落的区域内滑坡发育程度不同,反映了不同段落发震构造的特征差异。滑坡的主体分布范围与震中位置表明了构造破裂是从SEE向NWW方向发展的。最后,分析了该滑坡主体分布区中心线与临潭-宕昌断裂在空间地理位置上相差10km的2种可能的原因。

... 许冲等, 2013 ...

1999

0.0

袁道阳, 石玉成, 刘百篪. 1999. 青藏高原东北缘地区晚第四纪水系沉积物年代标尺的初步研究[J]. 地震地质, 21(1): 1—8.

YUAN

Dao-yang

, SHI

Yu-cheng

, LIU

Bai-chi

. 1999. Study on the time scale of late Quaternary hydrogenic sediments along the northeastern margin of Qinghai-Xizang Plateau[J]. Seismology and Geology, 21(1): 1—8(in Chinese).

The comparative research of the river terraces along the northeastern margin of Qinghai Xizang plateau indicates that the heights and ages of terraces of different grade rivers are quite different. But there is correlation between the heights and the ages. A statistical relationship formula is proposed. The terrace ages of river and the drainage system are compared with the ages of paleosoil in the loess profile. The results indicate that the development of terrace is controlled by tectonics and climate. We can use the paleosoil ages of Lanzhou area loess profiles (one of the standard loess profiles) to establish an initial late Quaternary microgeomorphogy time scale. The vertical rising rates reflected by the terraces show that since 1.5Ma the northeastern margin of Qinghai Xizang plateau are continuelly rising with a tendency of becoming quicker. During mid Pleistocene the rise rate is about 0.1～0.25mm/a. Since late Pleistocene to Holocene, the rise rate is about 0.5～1.5mm/a. The relationship between the rise rates and ages has been changed with time.

Lanzhou Institute of Seismology, China Seismological Bureau, Lanzhou 730000

对青藏高原东北缘地区河流阶地资料的对比研究表明,阶地的高度与阶地的形成年代之间具一定相关性,同时,阶地的形成年代与黄土剖面中古土壤年代完全可以对比,因此,以阶地的高度代替阶地级数,并借用兰州地区黄土标准剖面的古土壤年代,建立了青藏高原东北缘地区晚第四纪水系沉积物的年代标尺。阶地抬升速率研究表明,大约自150万a以来,青藏高原东北缘地区正在进行着持续的构造抬升,并且呈越来越快的趋势。

... 样品测年结果和上述阶地剖面沉积分析吻合较好, 中部黄黏土层的¹⁴C校正年龄为7170~7310a, 而上部黄土层底部2个¹⁴C样品的校正年龄分别为315~500a和795~970a, 黄土底部的¹⁴C样品年龄明显不符合冲沟T2阶地的经验预期, 测试结果显著偏小(袁道阳等, 1999) ...

2004

0.0

袁道阳, 张培震, 刘百篪, 等. 2004. 青藏高原东北缘晚第四纪活动构造的几何图像与构造转换[J]. 地质学报, 78(2): 270—278.

YUAN

Dao-yang

, ZHANG

Pei-zhen

, LIU

Bai-chi

, et al. 2004. Geometrical imagery and tectonic transformation of late Quaternary active tectonics in northeastern margin of Qinghai-Xizang Plateau[J]. Acta Geologica Sinica, 78(2): 270—278(in Chinese).

青藏高原东北缘所在的柴达木-祁连活动地块内的晚第四纪活动构造可以划分为主边界左旋剪切构造带、块内次级右旋剪切构造带和挤压会聚构造带等三种基本类型。在区域北东向构造应力作用下,块体发生了NE向的挤压缩短、顺时针方向的旋转和向SEE方向的挤出等构造变形。在块体内部形成了挤压推覆构造、次级剪切构造、剪切压扁构造和弧形挤出构造等四种典型的构造转换方式,实现不同方向与不同性质活动构造之间的转换平衡。

... 该地区发育了大量结构复杂、性质各异的活动断裂, 且大地震频发( 图 1)(袁道阳等, 2004 ...

... 形断裂系(尤其是NWW向断裂系)共同吸收和分配了2条边界断裂的差异运动(袁道阳等, 2004 ...

... 65mm/a, 与袁道阳等(2004)估算的2~2 ...

2006

0.0

张培震, 郑德文, 尹功明, 等. 2006. 有关青藏高原东北缘晚新生代扩展与隆升的讨论[J]. 第四纪研究, 26(1): 5—13.

ZHANG

Pei-zhen

, ZHENG

De-wen

, YIN

Gong-ming

, et al. 2006. Discussion on late Cenozoic growth and rise of northeastern margin of the Tibetan plateau[J]. Quaternary Sciences, 26(1): 5—13(in Chinese).

The Tibetan Plateau provides an outstanding field laboratory for studies of lithospheric dynamics and of the effects of large-scale topography on the earths atmosphere and, by extension, on climate. On a regional scale, the warming of air over Tibet is commonly interpreted to be a major factor that makes the Indian Monsoon the model for monsoonal circulations. Conversely, suggestions of a strengthening of the monsoon at ca.8MaB.P. have been used as arguments for an abrupt ca.1000-m rise of Tibets surface elevation, and therefore as support for proposed deeper mantle processes. Northeastern Tibet offers both a missing link in our understanding of Tibets overall growth and an ideal field laboratory in itself for studies of both how and why high, regionally extensive plateaux grow and how such terrains affect regional climate. We summarize recent studies of Late Cenozoic tectonic deformation in the Liupan Shan, Jishi Shan, Qilian Shan as well as their adjacent basins, to show that approximate coeval deformation occurred during 5~10MaB.P. or near 8MaB.P. in northeastern margin of the Tibetan Plateau. This tectonic event poses profound impacts on geomorphology, paleoclimate, and environment around the Tibetan Plateau. The tectonic acceleration and mountain uplift also occur during this time interval in the Altyn Tagh along Tibets northern boundary, and the Longmen Shan and Sichuan-Yunnan Plateau. All of these coeval events are manifestations of outward growth of the Tibetan Plateau near ca.8MaB.P. The outward growth is tectonically characterized by north northeastward convergence thrust faulting, folding, strike-slip faulting, and associated mountain uplift and sedimentary basin extinction. It is also this outward growth that set up the modern pattern of environments in and around the Tibetan Plateau.

State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing100029

青藏高原晚新生代的扩展和隆升对周边环境演变产生重大影响,确定扩展和隆升的起始年代是一个重要的科学问题。近年来在六盘山、积石山和祁连山及其相邻盆地的研究表明,青藏高原东北缘晚新生代(5~10MaB.P. 或约8MaB.P. )发生了准同期、影响深远的构造变形,导致了沉积盆地的消亡和山脉的隆起。青藏高原北缘的阿尔金山和东缘的岷山、龙门山及川滇高原也在该时段发生了构造活动的加速和构造隆升。所有这些准同期的事件反映了约8MaB.P. 前后青藏高原向周边的扩展,扩展的方式是通过一系列逆冲断裂、褶皱变形、左旋走滑及其伴随的山脉隆起和盆地消亡而实现的。该时期青藏高原的扩展导致了周边的环境变化,奠定了今日环境的格局。

... 1 区域构造晚新生代以来, 青藏高原周缘向NE扩展和挤出, 受到鄂尔多斯、阿拉善、四川盆地等坚硬地块的阻挡, 在高原边缘发生了复杂的构造变形(张培震等, 2006) ...

2013

0.0

张元生, 冯红武, 陈继峰, 等. 2013. 基于地震学资料探讨2013年岷县漳县6. 6级地震发震构造[J]. 地震工程学报, 35(3): 419—424.

ZHANG

Yuan-sheng

, FENG

Hong-wu

, CHEN

Ji-feng

, et al. 2003. Study on seismogenic structure of 2013 Minxian-Zhangxian M_S6. 6 earthquake with seismological data[J]. China Earthquake Engineering Journal, 35(3): 419—424(in Chinese).

Velocity and Qvalue tomography,in addition to precise positioning methods of small earthquakes,were used to obtain the deep structure of seismic source area and spatial distribution images of aftershocks.The data of velocity and Qvalue imaging consist of two parts.The first includes the observation data from a high-density portable seismic array consisting of 150 stations with a reporting period of November 2009 to November 2011 in the area of 32.2-36°N,102.8-107.1°E.The second includes data from a fixed network during the period of 1970-2010.Fromthese datasets,we selected 6 334seismic events recorded by at least 8stations and conducted velocity and Qvalue inversion calculation.We applied the three-dimensional grid search method to aftershock relocation,in which 746seismic events met with S-P arrival time differences detected by at least three stations.Finally,we obtained the relocation results of 400seismic events,and we applied the same method to relocation of the Minxian MS5.2earthquake occurring on November 13,2003,and the Minxian-Zhuoni MS5.0earthquake occurring on September 7,2004.We set the P1profile perpendicular to the direction to research in the deep distribution of the seismogenic fault.The profile P1crosscut the Lintan-Tanchang fault and the Minxian-Zhangxian seismic source area.We obtained the velocity profile,Q value profile,and aftershock distribution,which were combined with the focal mechanism solutions of these three earthquakes and the distribution of smaller earthquakes recorded since instrumental record have been kept.The results show that the seismogenic fault of Minxian-Zhangxian MS6.6earthquake is a buried fault with a NW strike direction,SW dip direction,and a dip angle steeper in the shallow region.In addition,the fault is thrust and sinistral strike-slip,and its exposure at the surface is 20km from Minxian section of the Lintan-Tanchang fault.The seismogenic fault and the Minxian section of the Lintan-Tanchang fault may have met at a deep level to form a fault zone to the south with a NW dip direction.The seismogenic faults of the Minxian MS5.2,Minxian-Zhuoni MS5.0,and Minxian-Zhangxian MS6.6earthquakes may belong to the same fault.The seismogenic fault of the Minxian-Zhangxian MS6.6earthquake is located in the suture parts of two secondary blocks.The east block is relatively stable,and the west block moves eastward and is blocked by the east block to form the extrusion area.The Qvalue of the extrusion area is lower and shows velocity uplift.In the Earth＇s crust of the west block,the Qvalue is lower,which provides eastward movement of west block with more favorable conditions.The occurrence region for earthquakes of MS≥5has included three events since 2003with seismogenic faults at least 20km from the Lintan-Tanchang fault;the dip direction is contrary.The seismogenic fault is located in the southwestern edge of Zhangxian＇s southern block,which is a secondary block(triangle)with a stable internal region.Three strong earthquakes occurred in western boundary of this block,which is conducive to the strain energy accumulation of the eastern region and the northern edge,which is the north rim fracture of western Qinling.The eastern region and northern boundary will likely be main regions of seismic activity of the southeast area of Gansu for the next several years.

应用速度和Q值成像方法以及小震精定位方法获得了2013年岷县漳县6.6级地震震源区的深部结构和余震序列的空间分布图像。结果表明:发震断层为一隐伏断裂,走向NW,倾向SW,逆冲兼左旋走滑,在地表距临潭-宕昌断裂岷县段约20km,在深部可能与临潭-宕昌断裂交汇在一起,向南组成一条NW向的断裂带。2003年11月13日岷县MS5.2、2004年9月7日岷县-卓尼MS5.0和本次MS6.6地震的发震断层可能属同一发震断层,位于漳县南部块体的西南边缘;该块体为次级块体(三角形),近几年来块体西南边界强震活跃,其它两边平静。

... 6地震( 图 1)发生后, 开展的大量相关研究集中于震源特征(张元生等, 2013 ...

2015

0.0

... 赵凌强等, 2015a, b)、震前异常分析(刘君等, 2013 ...

2015

0.0

赵凌强, 詹艳, 赵国泽, 等. 2015b. 基于深部电性结构特征的2013年甘肃岷县漳县 M_S6. 6地震孕震环境探讨[J]. 地震地质, 37(2): 541—554. doi: 103969/j. issn. 0253-4967. 2015. 02. 016.

ZHAO

Ling-qiang

, ZHAN

Yan

, ZHAO

Guo-ze

, et al. 2015b. The seismogenic environment of the 2013 Minxian-Zhangxian M_S6. 6 earthquake based on the deep electrical structure[J]. Seismology and Geology, 37(2): 541—554(in Chinese).

On July 22, 2013, an M S 6.6 earthquake occurred at the junction of Minxian and Zhangxian. After the earthquake, magnetotelluric(MT)measurement was carried out at 45 sites along the NE-oriented profile across the West Qinling orogen(the west segment)and the earthquake area. Remote reference, "robust", and phase tensor decomposition techniques were used to process the MT data, and the NLCG two-dimensional inversion method was adopted to get the deep electrical structures. The deep electrical structure images indicate that there exists an inverted trapezoidal high-resistivity layer in the West Qinling orogenic belt(west segment)at the depth from the surface to about 20km deep, which is shallow in the northeast and southwest and deep in the middle. Under the high-resistivity layer is a low-resistivity layer, and they conjoin each other. There is a low-resistivity layer in the Songpan-Ganzi block(north part)at the southwest side of West Qinling orogenic belt(west segment)under the depth of 20km in the lower crust, which is shallow in the northeast and deep in the southwest, and the Longxi Basin at its northeast has a stable layered structure, suggesting that West Qinling orogenic belt(west segment)is being subject to the northward extrusion of the Songpan-Ganzi block and southward resistance of the Longxi Basin. The East Kunlun Fault(Tazang segment)faulted the low-resistivity layer in the lower crust of Songpan-Ganzi block. The Diebu-Bailongjiang Fault and Guangaishan-Dieshan Fault zone extend to a shallow depth and merge into the East Kunlun Fault(Tazang segment)in the deep part. The characteristic of low-resistivity of the media in the deep-seated structures in the East Kunlun Fault(Tazang segment)is the underlying cause for the gradual decrease of horizontal slip rate and gradual increase of vertical movement of the Tazang segment. The West Qinling Fault is a main geoelectric boundary zone, which extends through the Moho; Lintan-Tanchang Fault zone behaves as a low-resistivity layer with a certain width, which extends into the low-resistivity layer in the mid to lower crust. The source region of Minxian-Zhangxian M S 6.6 earthquake locates in the core of inverted "trapezoid" of the low-resistivity layer in the West Qinling orogenic belt(west segment), that is, in the contact area between the high to low resistivity layers, and also in the low-resistivity fractured zone near the Lintan-Tanchang Fault. The interaction of southwest-northeast pushing from Songpan-Ganzi block and resistance of Longxi Basin block at its northeast is external dynamics of the Minxian-Zhangxian M S 6.6 earthquake, and the high- and low-resistivity medium property and their contact relation in the seismic source region of the earthquake are the internal factor to generate this earthquake.

1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. The Second Monitoring and Application Center, China Earthquake Administration, Xi'an 710043, China

2013年7月22日甘肃岷县漳县交界处发生 M S 6.6地震后,横跨西秦岭造山带和地震区沿NE方向的剖面进行了45个大地电磁测点的观测。使用远参考和 "Robust"技术以及相位张量分解技术处理数据, 采用NLCG 2维反演方法, 获得的深部电性结构图像揭示: 西秦岭造山带自地表至深度约20km存在东北和西南浅、中部深的倒 "梯形"高电阻体, 在高阻体之下为低电阻层, 高、低电阻层相互契合; 西秦岭造山带西南侧的松潘-甘孜地块(北部)在深度约20km存在西南深、东北浅的中下地壳低阻层, 其东北侧的陇西盆地具有稳定的成层性结构, 显示出西秦岭造山带正处于松潘-甘孜地块向北挤压和陇西盆地向南的阻挡挤压作用中。东昆仑断裂带(塔藏段)错断了松潘-甘孜地块中下地壳低阻层, 迭部-白龙江断裂和光盖山-迭山断裂带延伸深度不大, 在深部归并于东昆仑断裂带(塔藏段), 东昆仑断裂带(塔藏段)内部结构和介质的低阻特性是东昆仑断裂带在塔藏段水平滑动速率逐渐减小、垂向运动逐渐增强的深层原因。西秦岭北缘断裂为陡立的大型电性边界带, 延伸深度穿过莫霍面; 临潭-宕昌断裂带表现为具有一定宽度的低阻带, 延伸深度归并到中下地壳低阻层中。2013年甘肃岷县漳县6.6级地震震源区处于倒 "梯形"高阻体的西秦岭造山带的核部, 即位于高低电阻体接触区, 同时发生在低阻破碎带的临潭-宕昌断裂带附近。松潘-甘孜地块从SW向NE推挤、东北侧陇西盆地阻挡的相互作用是2013年岷县漳县 M S 6.6地震发生的动力学原因, 岷县漳县地震震源区特殊的高低阻介质属性和接触关系是该次地震发生的内部因素。

... 赵凌强等, 2015a, b)、震前异常分析(刘君等, 2013 ...

2007

0.0

... 前人对上述地震开展过史料考证和发震构造研究, 由于受到强烈的自然侵蚀和人为改造的影响, 断错地貌难以保留, 针对发震构造的研究仍较薄弱(郑文俊等, 2005, 2007a,b ...

2007

0.0

2005

0.0

2013

0.0

郑文俊, 闵伟, 何文贵, 等. 2013a. 2013年甘肃岷县漳县6. 6级地震震害分布特征及发震构造分析[J]. 地震地质, 35(3): 604—615. doi: 103969/j. issn. 0253-4967. 2013. 03. 014.

ZHENG

Wen-jun

, MIN

Wei

, HE

Wen-gui

, et al. 2013a. Distribution of the related disaster and the causative tectonic of the Minxian-Zhangxian M_S6. 6 earthquake on July 22, 2013, Gansu, China[J]. Seismology and Geology, 35(3): 604—615(in Chinese).

On July 22,2013,the Minxian-Zhanxian M S 6.6 earthquake occurred at the central-northern part of the South-North Seismic Belt. In the area,complicated structural geometries are controlled by major strike-slip fault zones,i.e.the Eastern Kunlun Fault and the Northern Frontal Fault of West Qinling. The distribution of related seismic disasters,namely,the ellipse with its major axis trending NWW,is in good accord with the strike of the Lintan-Tanchang Fault. Severe damages in the meizoseismal area of the Minxian-Zhangxian M S 6.6 earthquake are located within the fault zone. So it is considered that the earthquake related damages are closely related to the complicated geometry of the Lintan-Tanchang Fault,and it also indicates that the earthquake is the outcome of joint action of its secondary faults. Based on field investigations,and by integrating the results of previous studies on active tectonics,structural deformation and geophysical data,it can be inferred that the southward extension of the Northern Frontal Fault of West Qinling and the northeastward extrusion of the Eastern Kunlun Fault in the process of northeastward growth of Tibetan plateau are the main source of tectonic stress. Basic tectonic model is provided for strong earthquake generation on the Lintan-Tanchang Fault.

1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 3. Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China; 4. China Earthquake Disaster Prevention Center, Beijing 100029, China

2013年7月22日,甘肃岷县漳县 M S 6.6地震发生在南北地震带的中北段,东昆仑断裂和西秦岭北缘断裂是该地区复杂多样的构造几何特征中2条主要的边界控制断裂。这次地震的震害分布与临潭-宕昌断裂的走向基本一致,为长轴走向NWW的椭圆,极震区内严重破坏范围也完全位于该断裂带内,这与临潭-宕昌断裂复杂的几何结构密切相关,也说明地震的发生是多条次级断裂共同作用的结果。综合分析认为,受西秦岭北缘断裂带向南侧的扩展和青藏高原向NE扩展过程中东昆仑断裂带的NE向挤压作用共同影响下的临潭-宕昌断裂是这次地震的发震构造。

... 郑文俊等, 2013a ...

... 郑文俊等, 2013a, b) ...

2013

0.0

郑文俊, 袁道阳, 何文贵, 等. 2013b. 甘肃东南地区构造活动与2013年岷县-漳县 M_S6. 6地震孕震机制[J]. 地球物理学报, 56(12): 4058—4071.

ZHENG

Wen-jun

, YUAN

Dao-yang

, HE

Wen-gui

, et al. 2013b. Geometric pattern and active tectonics in southeastern Gansu Province: Discussion on seismogenic mechanism of the Minxian-Zhangxian M_S6. 6 earthquake on July 22, 2013[J]. Chinese Journal of Geophysics, 56(12): 4058—4071(in Chinese).

Southeast Gansu province along the central-northern portion of the South-North Seismic Belt, the tectonic activities and deformation pattern are closely related to the northeastward growth of the Tibetan Plateau. Complicated structural geometries were controlled by both Eastern Kunlun and West-Qinling Northern Faults, and outward growth of the NE Tibet continuously contributes to the regional active deformation. In recent years, intermediate-strong earthquakes occurred frequently, calling for a detailed analysis. By integrating both structural and historical seismicity studies, and combining geophysical, seismological and field investigations, we conclude that northward indenting and eastward movement along the Eastern Kunlun Fault is the main tectonic stress source, and also it provides the basic setting and mechanism to generate strong earthquakes. Left-lateral slip and its bi-flanking thrusting 'flower structure' of the West-Qinling Northern Fault contributed to the frequent occurrence of intermediate-strong earthquakes along the Lintan-Tanchang fault to the south. Minxian-Zhangxian M(S)6. 6 earthquake on July 22, 2013 along the central-eastern Lintan-Dangchang fault is a consequence of differential activity due to heterogeneous segments.

Zheng Wen-Jun 1 ;Ren Zhi-Kun 1 ;Yuan Dao-Yang 2 ;He Wen-Gui 2 ;Liu Xing-Wang 2 ;Wang Ai-Guo 2 ;Ge Wei-Peng 1,2 ;Min Wei 3 ;Xu Chong 3 ;Li Feng 3,4 ;

位于南北地震带中北段的甘东南地区，其构造变形和构造活动特征与青藏高原向北东方向的扩展密切相关，该地区复杂的构造几何形态主要受控于东昆仑断裂和西秦岭北缘断裂，区域新构造运动主要动力来源于青藏高原向北东的扩展.近年来，甘东南地区中强地震频发，本文主要通过对该地区构造活动特征、历史地震等资料的综合分析讨论，结合地球物理、地震学和野外调查等资料，认为青藏高原东北部东昆仑断裂的向北挤压和向东的运动是该地区构造应力集中的主要原因，也是该地区中强地震的主要孕震环境和机制，而西秦岭北缘断裂的走滑及向南北两侧逆冲“花状构造”是临潭—宕昌断裂带上中强地震频繁发生的一个重要动力因素.2013年7月22日发生在甘肃岷县—漳县的 M S 6.6级地震正好位于临潭—宕昌断裂带中东段上，是该断裂分段不均匀活动的结果.

... 郑文俊等, 2013a, b) ...

... 郑文俊等, 2013b) ...

2016

0.0

... 郑文俊等, 2016) ...

1986

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... 由东昆仑断裂、西秦岭北缘断裂、龙门山断裂等围陷的西秦岭次级块体, 其变形不仅发生在块体边界断裂上, 块体内部的弧形断裂系也发生相同量级的变形, 说明西秦岭的构造变形是跨区域、分布式的连续变形, 本文的研究结果倾向于支持连续变形理论(England et al ...

2014

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... Johnson et al ...

2017

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... 2程序(Ramsey, 2017)校正得到该事件发生的时间区间(置信度为2#cod#x003c3 ...

2013

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2012

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... 基于移动模型构建(Structure from Motion, SfM)(Westoby et al ...

2014

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... Xu et al ...

2012

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... 根据Zielke等(2012)开发的Ladicaoz软件测量得到冲沟右岸T2阶地前缘的左旋位错为8 ...