利用构造地貌分析日月山断裂晚更新世以来的演化

引用本文

李智敏, 李文巧, 殷翔, 黄帅堂, 张军龙. 利用构造地貌分析日月山断裂晚更新世以来的演化[J]. 地震地质, 2019,41(5): 1077-1090.
LI Zhi-min, LI Wen-qiao, YIN Xiang, HUANG Shuai-tang, ZHANG Jun-long. ANALYSIS OF EVOLUTION OF THE RIYUESHAN FAULT SINCE LATE PLEISTOCENE USING STRUCTURAL GEOMORPHOLOGY[J]. SEISMOLOGY AND GEOLOGY, 2019,41(5): 1077-1090. 复制到剪切板

DOI:10.3969/j.issn.0253-4967.2019.05.001
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利用构造地貌分析日月山断裂晚更新世以来的演化

李智敏^1,², 李文巧⁴, 殷翔¹, 黄帅堂³, 张军龙^4,^*

1)青海省地震局, 西宁 810001

2)深圳防灾减灾技术研究院, 深圳 518003

3)新疆维吾尔自治区地震局, 乌鲁木齐 830011

4)中国地震局地震预测研究所, 地震预测重点实验室, 北京 100036

*通讯作者: 张军龙, 男, 1973年生, 副研究员, 主要从事新构造、地震地质方面的研究, E-mail: 448092692@qq.com。

〔作者简介〕李智敏, 男, 1977年生, 2005年于中国地震局兰州地震研究所获构造地质专业硕士学位, 副研究员, 现主要从事活动构造及其次生灾害方面的研究工作, 电话: 0755-82616372, E-mail: minhero_168@126.com。

收稿日期: 2019-05-13

基金项目: 青海省科技计划项目(2017-ZJ-775)、中央级公益性科研院所基本科研业务专项(JB-18-03)和国家自然科学基金(41372215)共同资助

摘要

日月山断裂位于东昆仑断裂和祁连-海原断裂等主边界断裂控制的柴达木-祁连活动块体内部, 属于二级构造。该断裂构造地貌发育, 研究其活动特征可获得青藏高原东北缘向外扩展的信息。文中以晚更新世以来清晰的地貌变形为重点, 通过RTK测量方法获得沿断层走向的垂直位移量, 基于断层生长连接理论, 分析了日月山断裂的演化, 并讨论其反映的动力学背景, 主要获得了以下3点认识: 1)根据晚更新世以来洪积扇和阶地等地貌内长约200km的3期断层陡坎的发育特征, 将日月山断裂分为5段, 最重要的分段位于第三重叠区(CD-3)。 2)日月山断层3期位移量分布形态反映了断层由多条次级破裂生长连接而成, 处于断层生长连接的第二阶段。以CD-3为界, NW侧的断层持续生长连接; 东南侧的断层活动时间相对较短, 活动强度相对较弱。 3)断层位移量分布曲线极值指示了应变集中和应力积累的位置。以CD-3重叠区为界, NW侧应力和应变主要集中在中部及断层重叠区, 东南侧应力长期积累的范围则相对分散。应力状态可能与区域构造应力挤压作用下块体内部的顺时针旋转有关。

关键词: 青藏高原; 日月山断裂; 晚更新世; 几何分段; 断层生长

中图分类号:P315.2 文献标志码:A 文章编号:0253-4967(2019)05-1077-14

ANALYSIS OF EVOLUTION OF THE RIYUESHAN FAULT SINCE LATE PLEISTOCENE USING STRUCTURAL GEOMORPHOLOGY

LI Zhi-min^1,², LI Wen-qiao⁴, YIN Xiang¹, HUANG Shuai-tang³, ZHANG Jun-long⁴

1)Qinghai Earthquake Agency, Xining 810001, China

2)Shenzhen Academy of Disaster Prevention and Reduction, Shenzhen 518003, China

3)Earthquake Agency of Xinjiang Uygur Autonomous Region, Urumqi 830011, China

4)Key Laboratory of Earthquake Predication, Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China

Abstract

The northeastern margin of Tibetan plateau is an active block controlled by the eastern Kunlun fault zone, the Qilian Shan-Haiyuan fault zone, and the Altyn Tagh fault zone. It is the frontier and the sensitive area of neotectonic activity since the Cenozoic. There are widespread folds, thrust faults and stike-slip faults in the northeastern Tibetan plateau produced by the intensive tectonic deformation, indicating that this area is suffering the crustal shortening, left-lateral shear and vertical uplift. The Riyueshan Fault is one of the major faults in the dextral strike-slip faults systems, which lies between the two major large-scale left-lateral strike-slip faults, the Qilian-Haiyuan Fault and the eastern Kunlun Fault. In the process of growing and expanding of the entire Tibetan plateau, the dextral strike-slip faults play an important role in regulating the deformation and transformation between the secondary blocks. In the early Quaternary, because of the northeastward expansion of the northeastern Tibetan plateau, tectonic deformations such as NE-direction extrusion shortening, clockwise rotation, and SEE-direction extrusion occurred in the northeastern margin of the Tibetan plateau, which lead to the left-lateral slip movement of the NWW-trending major regional boundary faults. As the result, the NNW-trending faults which lie between these NWW direction faults are developed. The main geomorphic units developed within the research area are controlled by the Riyueshan Fault, formed due to the northeastward motion of the Tibet block. These geomorphic units could be classified as: Qinghai Lake Basin, Haiyan Basin, Datonghe Basin, Dezhou Basin, and the mountains developed between the basins such as the Datongshan and the Riyueshan. Paleo basins, alluvial fans, multiple levels of terraces are developed at mountain fronts. The climate variation caused the formation of the geomorphic units during the expansion period of the lakes within the northeastern Tibetan plateau. There are two levels of alluvial fans and three levels of fluvial terrace developed in the study area, the sediments of the alluvial fans and fluvial terraces formed by different sources are developed in the same period. The Riyueshan Fault connects with the NNW-trending left-lateral strike-slip north marginal Tuoleshan fault in the north, and obliquely connects with the Lajishan thrust fault in the south. The fault extends for about 180km from north to south, passing through Datonghe, Reshui coal mine, Chaka River, Tuole, Ketu and Xicha, and connecting with the Lajishan thrusts near the Kesuer Basin. The Riyueshan Fault consists of five discontinuous right-step en-echelon sub-fault segments, with a spacing of 2~3km, and pull-apart basins are formed in the stepovers.
The Riyueshan Fault is a secondary fault located in the Qaidam-Qilian active block which is controlled by the major boundary faults, such as the East Kunlun Fault and the Qilian-Haiyuan Fault. Its activity characteristics provide information of the outward expansion of the northeastern margin of Tibet. Tectonic landforms are developed along the Riyueshan Fault. Focusing on the distinct geomorphic deformation since late Pleistocene, the paper obtains the vertical displacement along the fault strike by RTK measurement method. Based on the fault growth-linkage theory, the evolution of the Riyueshan Fault and the related kinetic background are discussed. The following three conclusions are obtained: 1)According to the characteristics of development of the three-stage 200km-long steep fault scarp developed in the landforms of the late Pleistocene alluvial fans and terraces, the Riyueshan Fault is divided into five segments, with the most important segment located in the third stepover(CD-3); 2)The three-stage displacement distribution pattern of the Riyueshan Fault reveals that the fault was formed by the growths and connections of multiple secondary faults and is in the second stage of fault growth and connection. With CD-3 as the boundary, the faults on the NW side continue to grow and connect; the fault activity time on the SE side is shorter, and the activity intensity is weaker; 3)The extreme value of the fault displacement distribution curve indicates the location of strain concentration and stress accumulation. With the stepover CD-3 as the boundary, the stress and strain on NW side are mainly concentrated in the middle and fault stepovers. The long-term accumulation range of stress on the SE side is relatively dispersed. The stress state may be related to the counterclockwise rotation inside the block under the compression of regional tectonic stress.

Keyword: Qinghai-Tibet Plateau; Riyueshan Fault; Late Pleistocene; geometric segmentation; fault growth

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0 引言

青藏高原东北缘是由东昆仑断裂带、祁连山-海原断裂带以及阿尔金断裂带控制的活动地块, 是新生代以来新构造活动的前沿地带和敏感部位。晚新生代以来, 青藏高原东北缘构造变形强烈, 区内遍布褶皱、逆冲和走滑断裂, 表明该区正处于地壳缩短、左旋剪切并伴随垂直隆升作用的阶段(邓起东等, 2002, 2004, 2008; 张培震等, 2006, 2013)。青藏高原东北缘的构造变形定量研究主要集中在北祁连山— 河西走廊地区(袁道阳等, 1997; 冉勇康等, 1998; 田勤俭等, 2000, 2006; 郑文俊等, 2004, 2009, 2012; 付碧宏等, 2006; 徐锡伟等, 2007; 郑文俊, 2009), 但关于块体内部活动断裂的构造变形量和构造变形演化过程的研究却相对缺乏, 如针对南祁连地区的日月山断裂、鄂拉山断裂以及拉脊山断裂等的相关研究较少, 限制了地学工作者对该块体内部变形机制的认识。

日月山断裂作为一条重要的块体内部断裂, 其几何分段和地貌年龄研究取得的成果(袁道阳等, 2003b; Yuan et al., 2011; 李智敏等, 2018)为构造地貌变形的定量研究提供了有利基础。因此, 本文选择日月山断裂作为研究区域, 通过测量晚更新世以来各段的构造地貌变形量, 基于断层生长连接理论, 讨论日月山断裂各段的构造地貌变形中所反映的构造演化过程。本工作不仅有益于认识该断裂的活动特征, 也可为认识区域构造变形样式提供重要依据(邓起东等, 2008), 所得结论对于认识青藏高原东北缘的运动方式具有重要理论意义, 同时对评价该断裂的地震危险性具有参考作用。

1 研究区域概况

日月山断裂位于青藏高原东北缘柴达木-祁连活动地块的内部。柴达木-祁连活动地块受东昆仑断裂、祁连-海原断裂和阿尔金断裂所控制(图1a), 日月山断裂属于夹持于主边界断裂之间的一系列次级构造之一。由于青藏块体向NE扩展, 致使NWW向的区域主边界断裂发生左旋走滑, 而夹持于其间的NNW向日月山断裂被剪切压扁, 其运动性质为右旋走滑兼逆冲作用(Yuan et al., 2011; 李智敏等, 2018)。

日月山断裂北部与NNW走向的托勒山北缘左旋走滑断裂相接, 南部与拉脊山逆冲断裂斜接。断裂自北向南经过大通河、热水煤矿、茶拉河、托勒、克图和西岔, 最终在克素尔盆地附近与拉脊山断裂相接, 全长180km。断裂由5条不连续的次级断裂段右阶羽列而成, 阶距2~3km, 在不连续部位形成拉分区。主断裂两端则形成帚状分叉(袁道阳等, 2003a; 李智敏等, 2013)(图1b)。

青藏块体向NE的不断扩展, 使得块体内部的日月山断裂控制了区域内不同类型地貌的发育, 形成了研究区内地貌的基本骨架。区内地貌可分为由断裂控制的青海湖盆地、海晏盆地、大通河盆地、德州盆地以及盆地之间的对冲山(如大通山和日月山), 山前和盆地之间发育有古盆地面、冲洪积扇体及多级河流阶地面。

青藏高原自湖泊扩张时期以来, 气候变化事件控制了青藏高原东北缘的地貌发育特征(施雅风等, 2002; 李建军等, 2016)。研究区域内发育2期洪积扇面和3级河流阶地面, 这些洪积扇和阶地属于同时期中的不同沉积类型, fp₁、 fp₂的时代约(3.6± 0.1)kaiBP、 (21.2± 0.6)kaiBP; 3级河流阶地面T₁、 T₂和T₃的年龄分别为4.8~7.0ka、 (12.4± 0.11)ka和23.8~33.0ka, 可相互进行对比(袁道阳等, 2003b; Yuan et al., 2011; 李智敏等, 2018)。 fp₁和T₁对应于早全新世温暖期向晚全新世干冷期转换的过渡时期(王燕等, 2006; 于学峰等, 2006); T₂对应于深海氧同位素MIS1阶段; fp₂和T₃对应于深海氧同位素MIS2阶段。日月山断层持续活动, 并伴生多种构造地貌类型, 晚更新世以来沿断裂在阶地面和洪积扇面上形成了清晰且较连续的线性陡坎, 坎高3~18m。

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图 1 研究区区域地震构造图
F₁龙首山北缘断裂; F₂龙首山南缘断裂; F₃民乐-永昌断裂; F₄莲花山北缘断裂; F₅民乐-大马营断裂; F₆皇城-双塔断裂; F₇肃南-祁连断裂(俄堡段); F₈托莱山断裂; F₉冷龙岭断裂; F₁₀门源断裂; F₁₁达坂山断裂; F₁₂拉脊山断裂; F₁₃日月山断裂; F₁₄木里-江仓断裂带; F₁₅二郎洞-茶卡杯断裂; F₁₆青海南山北缘断裂; F₁₇倒淌河-临夏断裂; F₁₈畦玉香卡- 拉干断裂; F₁₉鄂拉山断裂。 F_13-1大通河段; F_13-2热水段; F_13-3德州段; F_13-4海晏段; F_13-5日月山段Fig. 1 Seismic structural map of the study area.

2 垂向位移量测量方法与数据分析方法

基于前人对日月山断裂的几何分段和地貌面的研究成果, 本文首先识别各段晚更新世以来的地貌面(T₁— T₃和冲洪积扇, 为了便于对比不同地貌的垂直位移量, 参考冲洪积扇与相邻阶地的分布范围、高度和年龄, 将2期洪积扇与2期阶地相对应, 文中统一用阶地进行叙述), 同时确定断裂通过不同地貌面的位置。在此基础上, 在条件允许的地点(如7颗以上卫星信号覆盖、非基岩区), 利用RTK测量断层在各级阶地和冲洪积扇形成断错陡坎的高度。测量时, 测线垂直于断层走向, 间隔0.5~1km, 长度覆盖断层两侧各50~100m(获得未受断层影响区域的地貌面的坡度)。获得测线数据后, 基于断层两侧未受断层影响区域的地貌面中的多个测点绘制趋势线, 延伸至断层, 计算测线的斜率、截距以得到断层的垂直位移量。在无法测量的区域, 参考相邻测点的位移量, 以近对称形态推测空区的位移量, 进而获得区域的位移量分布形态。需要说明的是, 测量空区的位移量分布形态仅是推测结果, 真实形态尚需进一步研究。

获得的各级地貌面的垂直位移量记录了地貌形成和断裂演化之间的相互作用, 因此该位移量是进行断层运动学分析的最佳对象。

研究发现断层运动的结果除了引起断层位移随时间累积以外, 断层的长度也随时间增加。针对断层侧向长度增长过程中断层表现的形态以及位移量和长度之间的关系所进行的研究也取得了丰富的成果(Kim et al., 2005; Tvedt et al., 2013; Fossen et al., 2016; Peacock et al., 2017)。

断层生长连接过程的4阶段模式(图2)具体可描述为: 1)断层各自生长, 位移和长度同时增加, 其比值保持不变, 断层之间未发生重叠或相互作用, 单一断层位移剖面呈对称的倒“ V” 形或钟形(图2a); 2)断层之间发生重叠, 通过应力域发生相互作用, 且总位移在重叠处最小, 单一断层位移剖面呈不对称的几何形状, 且位移极值偏向连接处(图2b); 3)新生的连接断层逐渐将两侧小型断层连接并持续演化, 此时位移剖面似 “ M” 形(图2c); 4)两侧小型断层被新生的连接断层贯穿成一条大规模的断层, 在连接位置存在位移极小值(图2d), 随时间增加, 连接位置位移增长至与两侧相同, 随后, 断层连接进入下一次循环(Peacock et al., 1991)。

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	图 2 断层生长连接过程4个阶段的位移-长度图(Peacock et al., 1991)Fig. 2 Diagrams of stages of fault development and corresponding displacement-distance graphs.

3 结果

3.1 典型地段的地貌

断裂造成的不同阶地(扇体)地貌垂直位错所形成的断层陡坎与阶地陡坎在形态上有相似之处, 这往往会影响对断裂几何位置的判断, 进而影响垂直位移量的测量精度。为了避免阶地陡坎对断层陡坎的影响, 选择断层形迹线性特征明显且连续切割多级地貌面的位置进行测量。野外实际调查发现, 沿断层走向上3级阶地均有分布, 且保留完整的地点较少。阶地在热水段和德州段零星出现, 在其它段少见, 因此本文选择热水段和德州段2个典型地貌进行详细说明。

热水段典型地点(37.476i8° N, 100.524i2° E)地貌发育较完整。 T₃阶地仅分布在NE方向的邻近基岩区, 呈狭长的条带状, 与河流近平行; T₂和T₁阶地零星分布在河流之间; 冲洪积扇分布较广。断裂沿基岩山前分布, 呈线性切过3级阶地和冲洪积扇(图3)。利用DGPS测量得到T₃阶地被断层错断, 垂直断距约16m, 该值是沿断层所有测量点中最大的位移量; T₂阶地的垂直断距约7m; T₁阶地的垂直断距约2m(图3)。

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	图 3 热水段典型地貌解译图 a 原始的Google Earth影像, 位置见图1; b 解译图; c地形剖面, 剖面位置见3b。 fp₁为洪积扇面, T₁、 T₂为河流阶地面。1 基岩; 2 T₁阶地; 3 T₂阶地; 4 T₃阶地; 5 冲洪积扇; 6 断层; 7 测线位置Fig. 3 Geomorphic interpretation at Reshui.

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	图 4 德州段典型地貌解译图 a 原始Google Earth影像, 位置见图1; b解译图; c 无人机航测得到的DEM, 位置见4b; d 地形剖面, 剖面位置见图c。 fp为洪积扇面, T₁、 T₂为河流阶地面Fig. 4 Geomorphic interpretation at Dezhou.

另外1个典型地貌点位于德州段(37.102i8° N, 100.686i1° E), 老冲洪积扇(形成时代与T₃阶地相近)分布在出山口处, T₂和T₁阶地切割冲洪积扇体, 近平行分布于河流两侧, T₁分布范围较小。断裂呈线性切过2级阶地和冲洪积扇(图4)。在断层切过河流处, 选择断层陡坎明显的地点进行无人机测量, 冲洪积扇体的垂直断距约11m, T₂阶地面的垂直断距约4.5m, T₁阶地面的垂直断距约2m。

其它地点的地貌往往也发育2级阶地或冲洪积扇, 使用DGPS测量多级地貌面以对比各级地貌变形产生的垂直位移量。

3.2 各断裂段的陡坎特征

除各段重叠区受后期河流改造影响的区域和因山区自然条件限制无法布设测线的区域外, 在断裂各段均有测线分布, 累计149条, 间距0.6~2km, 平均间隔1km布设1条测线, 以便控制位移量的空间图形(图5)。

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	图 5 日月山断层分段及垂直位移量分布图 a 日月山断裂地貌图; b 日月山断裂分段及地表破裂示意图; c 沿断层走向断层垂直位移量分布图Fig. 5 The schematic diagram of segmentation of the Riyueshan Fault and the distribution of the vertical displacement.

大通河段全长43km, 布设了18条测线, 大通河段北部陡坎不明显, 南部断层发育在基岩山区中, 中部大通河盆地冲洪积扇体和阶地上存在线性的断层陡坎。 T₁期次陡坎高0.5~3.0m(平均为1.8m), 断层位移量分布呈齿状, 由3个极大值和2个极小值构成, 叠置区(CD-1)内(距断层北端点约45km处)有较小的位移量。根据极值分布可将T₁期陡坎分为长约10km、 5km及长度> 5km的3条次级破裂。 T₂期次陡坎高3.0~5.6m(平均为4.1m), 断层位移量分布呈齿状, 由2个极大值和2个极小值构成, 分为长约13km及长度> 8km的2条次级破裂。 T₃期次陡坎高6.0~8.4m(平均为7.2m), 仅可示倾斜形态。 T₁、 T₂和T₃期位移量的最大值均位于此段东南约3/4 处。 T₁、 T₂上断层的位移量呈齿状, 表明其由多条次级断层相接而成。位移最大处靠近叠置区CD-1, 且其内有较小位移量, 可能暗示断层向SE扩展, 以补充重叠区的位移量。

热水段全长55km, 分布了54条测线。全段线性断层陡坎均有分布。 T₁期次陡坎高0.5~2.9m(平均为1.8m), 断层位移量分布形态为齿状, 由7个极大值和7个极小值构成, 距断层北端点60~80km范围内位移量分布形态较宽缓, 与图2d的形态相似, CD-2内形迹不清楚, 可分为长度> 5km、长约5km、 11km、 10km、 3km、 8km和3km的7条次级破裂。 T₂期次陡坎高3.0~6.0m(平均为4.4m), 断层位移量分布呈齿状, 由3个极大值和2个极小值构成, 可分为长度> 8km、长约37km及长度> 5km的3条次级破裂。 T₃期次陡坎高13.6~15.8m(平均为14.7m), 仅可示倾斜形态。 T₁、 T₂和T₃的断层位移量最大值均向CD-1偏移, 位置依次约在距断层北端点 48km、 61km和70km处, 值得注意的是, T₁、 T₂在距断层北端点约95km、 91km处的垂直位移也接近最大值。 T₁、 T₂上断层的位移量呈齿状, 表明其由多条次级断层相接而成。 T₁在距断层北端点60~80km范围内位移量的分布形态可能指示部分次级破裂已经连接, 距断层北端点约70km处的位移量极小值与T₃位移量最大值所在的位置相近, 推测其原因是T₁时期的破裂位移量弥补了T₃时期的破裂位移量, 也佐证了部分次级破裂已经连接。 T₁、 T₂和T₃期次位移量最大值位置向CD-1偏移, 与大通河段的偏移相呼应, 与图2c形态相似, 佐证了CD-1属于断层连接区。位移量最大值的位置不同, 随着时间增长, 向CD-1偏移的距离增加, 靠近CD-2一侧也存在类似现象, 表明热水段持续向两侧扩展, 通过位移量来平衡该重叠区域的应变分配。 CD-2内位移量不清楚, 是受茶拉河及其支流后期改造的影响。

德州段全长24km, 分布有23条测线。在大部分地区的山前冲洪积扇体上可以发现一系列的断层陡坎, 距断层北端点115~123km处为山区, 未布设测线。 T₁期次陡坎高0.8~3.0m(平均为1.6m), 断层位移量分布呈不规则齿状, 由2个极大值和2个极小值构成, 可分为长度> 2km、长约8km的2条次级破裂。 T₂期次陡坎高3.4~5.8m(平均为5.0m), T₃期次陡坎高约11.0m, 断层位移量分布仅可示倾斜形态。 T₁、 T₂期次垂直位移量最大值出现的位置均向CD-2偏移, 位置依次在距断层北端点约105km和109km处。 T₁上断层的位移量呈齿状, 表明其由2条次级断层相接而成。 T₂、 T₃上断层的位移量数据不支持次级分段。 T₁、 T₂上断层的位移量最大值位置向CD-2偏移, 随着时间增长, T₂期次位移量最大值的位置向CD-2偏移的距离增加, 与热水段的偏移相呼应, 表明德州段持续向NW扩展。

海晏段全长约30km, 布设有37条测线, 中段陡坎较两端清晰。 T₁期次陡坎高0.3~2.5m(平均为1.2m), 断层位移量分布呈不规则齿状, 由4个极大值和4个极小值构成, 可以极小值(距断层北端点约132km处)为界划分为长度> 9km和长约14km的2条次级破裂。 T₂期次陡坎主要分布在海晏段NW侧长约5km的范围内, 高3.1~6.8m(平均为4.7m), 断层位移量分布仅可示倾斜形态。 T₃面不发育, 也未发现陡坎形迹。 T₁期次位移量值分布较其它段复杂, 在0.3~2.5m范围内浮动, 最大值位于距断层北端点约131km处, 略向CD-3偏移。 T₂期次位移量最大值位于距断层北端点约123km处, 毗邻CD-3。

日月山段全长约48km, 布设有17条测线, 该段受人为改造较严重, 只在中段部分冲沟口有原始陡坎出露。 T₁期次陡坎高0.4~2.8m(平均为1.6m), 断层位移量的分布为不规则齿状, 由5个极大值和5个极小值构成, 可以分为长约5km、 4km、 2km、 6km和长度> 17km的5条次级破裂, 以距断层北端点约183km处为界, 日月山段东南侧长度> 17km的次级破裂位移形态宽缓。 T₂期次陡坎仅在日月山段NW侧山前冲沟口(距断层北端点约165km处)出现, 高4.1m, 毗邻CD-4。 T₃面不发育, 其上也未发现陡坎形迹。 T₁上断层的位移量呈齿状, 表明由多条次级断层相接而成。 T₁期次位移量最大值位于距断层北端点约170km处, 第二大值位于距断层北端点约179km处, 与最大值相差很小, 2个位置构成的位移量分布形态显示的偏移方向不清晰, 表明2个位置所处的次级破裂具有相对独立的生长过程。日月山段东南侧长度> 17km的次级破裂位移形态宽缓, 因日月山段南接拉脊山断裂带, 此次级破裂的形态可能是受到南侧拉脊山断裂带的影响。另一方面, 此段大范围缺失T₂、 T₃阶地, 断层陡坎仅在日月山段的NW侧出现, 仅根据单一值无法确定断层位移量的形态, 只能推测其存在向NW扩展的可能, 但T₂期次位移量值也仅占相邻海晏段的60%, 表明即使存在扩展, 程度也较弱。

由此可知, T₁期断层陡坎断续延伸200km, 由4个重叠区划分为5个次级破裂段, 各段的形态如前文所述。断层整体的垂直位移量呈不规则齿状分布, 两侧呈单侧平缓倾斜状, 热水段中部呈对称性平缓状, 由17个次级破裂组成, 长度多为5~11km, 最长超过17km, 位于最南侧。各段的位移量最大值从大到小依次为大通河段、德州段(2段相等)、热水段、日月山段以及海晏段。

T₂期形迹清晰的断层陡坎断续延伸120km, 虽然南侧2段仅零星出露, 但仍然可以由4个重叠区划分为5个次级破裂段, 断层位移量分布的整体形态呈不规则齿状, 由超过7个次级破裂所组成, 长度多为5~13km, 最长37km, 位于热水段; 各段的位移量最大值从大到小依次为海晏段、热水段、德州段、大通河段和日月山段。除NW侧的大通河段外, 其余各段出现最大位移量的位置均向NW侧偏移。

T₃期断层陡坎残留形迹分布范围较小, 在日月山断裂带NW侧的3段零星出现该期残留断层陡坎, 东南侧的2段未见该期断层陡坎, 次级破裂划分模糊。各段位移量的最大值从大到小依次为热水段、德州段和大通河段。

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	图 6 日月山断裂分段沿断层走向断层垂直位移量模型Fig. 6 Vertical along-strike displacement model of each segment of the Riyueshan Fault.

4 讨论和结论

(1)日月山断裂的构造地貌以断层陡坎最为显著, 在晚更新世以来的冲洪积扇和阶地等地貌内断续分布长约200km的断层陡坎。从NW向SE, 沿断层走向, 均存在T₁、 T₂ 2期断层陡坎, T₃期断层陡坎在日月山断裂南部的2段缺失。地貌面上的陡坎分布及其垂直位移曲线被重叠区分隔, 时代越新的断层陡坎受断层重叠区控制越明显, 在断层重叠区陡坎形迹模糊或缺失, 断层重叠区之间形迹连续且清晰, 根据日月山断裂陡坎的分布及其垂直位移曲线形态可将断层分为5段, 与前人根据断层展布得到的几何分段相吻合。本文提出的最重要的分段应属于CD-3重叠区划分的NW侧(3段)和东南侧(2段), 两者的破裂形态、陡坎分布及垂直位移量曲线形态的差异尤为显著。

(2)日月山断层各期位移量的分布形态反映该断层是由多条次级破裂生长连接而成的(图6)。重叠区内未发现新生的连接断层的形迹, 暗示各段之间还处于断层生长连接的第二阶段。在各段内, T₁— T₃期次级破裂数量逐渐减少, 表明一些次级破裂随着时间增长已经发生连接, 为了弥补前期位移量的不足, 在连接处新的位移量相对较大, 如距断层北端点20~25km和80~96km处, T₁期陡坎的高位移量相对应T₂期的低位移量; 相反的现象出现在距断层北端点60~75km处, T₁期陡坎的低位移量相对应T₂期的高位移量。垂直位移量的持续积累形成T₃期似对称形的位移量曲线形态。以CD-3重叠区为界, T₁— T₃期最大(或次之)位移量基本位于NW侧3段内, 位移曲线形态基本相似, 说明存在持续的断层生长连接过程, 两侧的德州段、大通河段的极大值向中部热水段偏移, 说明这一过程仍在持续。东南侧2段T₃期陡坎缺失, T₂期陡坎在NW侧端部零星分布, T₁期位移最大处相对靠近中部。日月山断裂是青藏高原东北缘地区夹持于区域大型左旋走滑断裂内部的1套右旋走滑断裂中的一支, 并未切错大型块体的边界。考虑到日月山断裂地质背景基本相似, 故推测东南侧2段活动的时间不长, 活动强度相对NW侧较弱。

(3)断层位移分布曲线极值偏移方向受应变场叠加影响, 所在位置指示了应变集中和应力积累的位置(Kim et al., 2005; Peacock et al., 2017)。以CD-3重叠区为界, 日月山断裂NW侧3段内的极值多在中部热水段, 热水段两侧的德州段、大通河段的极大值位置向中部偏移, 说明应力主要集中在中部及断层重叠区。日月山断裂东南侧2段内T₂期的极值位于NW侧端部, T₁期极值相对靠近中部, 应力长期积累范围较分散。在青藏高原东北缘整体生长和扩展的过程中, 以祁连山-海原断裂带和东昆仑断裂带为代表的NWW— NW向大型主边界断裂与夹于其间的日月山断裂和鄂拉山断裂为代表的块体内部NNW向断裂可能构成了1组共轭构造(Yuan et al., 2011), 受NE向区域构造应力的挤压作用, 日月山断裂发生剪切压扁(袁道阳等, 2004), 形成垂直陡坎, 在各段端部产生的应力集中可能与块体内部的顺时针旋转有关(国家地震局地质研究所等, 1993)。

断层的生长和连接受岩性、几何结构和区域应力场等多因素影响, 对这些因素所造成的影响程度还需要讨论。断层的连接生长速率关系到后续断层破裂的位置和时间, 针对该问题还需要在详细研究阶地年龄后做进一步分析。

致谢审稿专家对论文提出了宝贵的修改意见, 在此表示衷心感谢!

The authors have declared that no competing interests exist.

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33	袁道阳, 刘小龙, 张培震, 等. 2003 a. 青海热水-日月山断裂带古地震的初步研究[J]. 西北地震学报, 25(2): 136—142. [本文引用:1]
34	YUAN Dao-yang, LIU Xiao-long, ZHANG Pei-zhen, et al. 2003 a. A preliminary study on palaeo-earthquake events of the Reshui-Riyue Mt. active fault zone in Qinghai Province[J]. Northwestern Seismological Journal, 25(2): 136—142(in Chinese). [本文引用:1]
35	袁道阳, 刘小龙, 张培震, 等. 2003 b. 青海热水-日月山断裂带的新活动特征[J]. 地震地质, 25(1): 155—165. [本文引用:2]
36	YUAN Dao-yang, LIU Xiao-long, ZHANG Pei-zhen, et al. 2003 b. Characteristics of the modern activity of the Reshui-Riyueshan fault zone in Qinghai Province[J]. Seismology and Geology, 25(1): 155—165(in Chinese). [本文引用:1]
37	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. [本文引用:1]
38	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). [本文引用:1]
39	张培震, 邓起东, 张竹琪, 等. 2013. 中国大陆的活动断裂、地震灾害及其动力过程[J]. 中国科学(D辑), 43(10): 1607—1620. [本文引用:1]
40	ZHANG Pei-zhen, DENG Qi-dong, ZHANG Zhu-qi, et al. 2013. Active faults, earthquake disasters and their dynamic processes in the mainland of China[J]. Science in China(Ser D), 43(10): 1607—1620(in Chinese). [本文引用:1]
41	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. [本文引用:1]
42	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). [本文引用:1]
43	郑文俊. 2009. 河西走廊及其邻区活动构造图像及构造变形模式 [D]. 北京: 中国地震局地质研究所. [本文引用:2]
44	ZHENG Wen-jun. 2009. Geometric pattern and active tectonics of the Hexi Corridor and its adjacent regions [D]. Institute of Geology, China Earthquake Administration, Beijing(in Chinese). [本文引用:1]
45	郑文俊, 袁道阳, 何文贵. 2004. 祁连山东段天桥沟-黄羊川断裂古地震活动习性研究[J]. 地震地质, 26(4): 645—657. [本文引用:1]
46	ZHENG Wen-jun, YUAN Dao-yang, HE Wen-gui. 2004. Characteristics of palaeo-earthquake activity along the active Tianqiaogou-Huangyangchuan Fault on the eastern section of the Qilianshan Mountains[J]. Seismology and Geology, 26(4): 645—657(in Chinese). [本文引用:1]
47	郑文俊, 张培震, 葛伟鹏, 等. 2012. 河西走廊北部合黎山南缘断裂晚第四纪滑动速率及其对青藏高原向北东扩展的响应[J]. 国际地震动态, (6): 30. [本文引用:1]
48	ZHENG Wen-jun, ZHANG Pei-zhen, GE Wei-peng, et al. 2012. Late Quaternary slip rates of the southern margin thrust fault of Heli Shan at the northern Hexi Corridor and their implications for northeastward growth of the Tibetan plateau[J]. Recent Developments in World Seismology, (6): 30(in Chinese). [本文引用:1]
49	郑文俊, 张培震, 袁道阳, 等. 2009. GPS观测及断裂晚第四纪滑动速率所反映的青藏高原北部变形[J]. 地球物理学报, 52(10): 2491—2508. [本文引用:1]
50	ZHENG Wen-jun, ZHANG Pei-zhen, YUAN Dao-yang, et al. 2009. Deformation on the northern of the Tibetan plateau from GPS measurement and geologic rates of Late Quaternary along the major fault[J]. Chinese Journal of Geophysics, 52(10): 2491—2508(in Chinese). [本文引用:1]
51	Yuan D Y, Champagnac J D, GE W P, et al. 2011. Late Quaternary right-lateral slip rates of faults adjacent to the lake Qinghai, northeastern margin of the Tibetan plateau[J]. Geological Society of America Bulletin, 123(9-10): 2016—2030. [本文引用:4]
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... 晚新生代以来, 青藏高原东北缘构造变形强烈, 区内遍布褶皱、逆冲和走滑断裂, 表明该区正处于地壳缩短、左旋剪切并伴随垂直隆升作用的阶段(邓起东等, 2002, 2004, 2008 ...

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2008

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邓起东, 闻学泽. 2008. 活动构造研究: 历史、进展与建议[J]. 地震地质, 30(1): 1—30.

This paper reviews the history and progresses of the research on active tectonics in China and overseas. By giving a brief introduction on histories of active tectonic researches in China and some other countries,the paper sums up the process and development on the quantitative investigation of active tectonics since the 1980's,and puts the focus on the main efforts and progresses that have been made in China on some aspects of the research,such as the basic survey and research and the applied investigation of active tectonics,the study on theories about regional active tectonics and their kinematics and geodynamics,the survey on the coupling relations between deep and shallow structures,the project on active fault survey and prospecting and seismic hazard assessment in urban areas,as well as the efforts on using the Quaternary geochronology. Further,the paper looks back to the Chinese efforts on the quantitative investigation of active tectonics,sums up those cognitions from studies on the determination of several basic and measurable parameters of active tectonics,such as the length of fault and fault-segment,coseismic slip and cumulative slip,fault slip rate,sequence of paleo-earthquake events,and the time elapsed from the latest event. At the same time,efforts and progresses in China on assessing long-term seismic potential for active fault and evaluating potential risk from potential active fault movement have been reviewed by summarizing researches on developing theories,models,methods and on application to the probabilistic assessment of time-dependent seismic potential,magnitude estimation for potential earthquake on active fault,and forecasting the potential risk caused by potential active fault movement. Finally,considering the realities and problems in the research of active tectonics in China,the authors put forward several suggestions for issues worthy of paying more attention to for further investigation in the future.

1. Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. China Earthquake Administration of Sichuan Province, Chengdu 610041, China

文中综述了国内外活动构造研究的历史与进展。在简要介绍国际以及中国早期活动构造研究历史的基础上,重点回顾了20世纪80年代以来活动构造及其定量研究的历史与发展,阐述了中国在活动构造基础调查研究、应用研究以及区域活动构造及其运动学、动力学理论研究等方面的主要工作与认识;进一步介绍了在活动构造定量参数测定方面的研究工作,以及基于这些定量参数进行的活动断裂潜在地震危险性与危害性评价工作与进展。最后,结合中国活动构造研究现状与存在的主要问题,提出今后宜重点加强工作的若干建议。

... 本工作不仅有益于认识该断裂的活动特征, 也可为认识区域构造变形样式提供重要依据(邓起东等, 2008), 所得结论对于认识青藏高原东北缘的运动方式具有重要理论意义, 同时对评价该断裂的地震危险性具有参考作用 ...

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2002

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2002

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2006

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付碧宏, 张松林, 谢小平, 等. 2006. 阿尔金断裂系西段——康西瓦断裂的晚第四纪构造地貌特征研究[J]. 第四纪研究, 26(2): 228—235.

The Tibetan Plateau is one of the most remarkable topographic features on Earth, and has widely taken to be the classic example of continent-continent collision. In the northern Tibet, the Altyn Tagh fault (ATF) system over 2000-km-long is the longest left-lateral strike-slip fault in the Asia, which accommodates sinistral motion between the Tibetan Plateau and the Tarim block within the India-Eurasia collision zone. The Kangxiwar Fault, extending over a length of 700km, is located on in northwestern Tibet as the western segment of the ATF.

①Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029; ②College of Geography &Environmental Science, Northwest Normal University, Lanzhou 730070; ③Department of Hydraulic Engineering, Tsinghua University, Beijing 100084; ④Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085

阿尔金断裂带是青藏高原北部的一条大型左旋走滑断裂带,近EW向延伸2000多公里, 它构成了青藏高原与塔里木盆地之间的重要地质边界。康西瓦断裂位于阿尔金断裂带西段, 呈WNW-ESE向延伸约 700km。文章在高分辨率卫星遥感图像(印度遥感卫星5.8m分辨率)和数字高程地形模型(DEM)数据分析的基础上,并结合野外构造地貌考察观测,对康西瓦断裂的第四纪构造活动及其地貌特征进行了初步研究。沿断裂带发育的系统错断水系、错断冲积扇、挤压脊、走滑拉分盆地等典型构造地貌特征表明,该断裂晚第四纪经历了强烈的左旋走滑活动。同时,研究还揭示沿康西瓦断裂发育了一条长约80km的地表地震破裂带,最大同震左旋水平错位为4m,估算产生该地表破裂带的地震是一矩震级为 M w 7.3的大地震。

... 付碧宏等, 2006 ...

2006

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... , 2011), 受NE向区域构造应力的挤压作用, 日月山断裂发生剪切压扁(袁道阳等, 2004), 形成垂直陡坎, 在各段端部产生的应力集中可能与块体内部的顺时针旋转有关(国家地震局地质研究所等, 1993) ...

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... 李建军等, 2016) ...

2016

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2018

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... 李智敏等, 2018)为构造地貌变形的定量研究提供了有利基础 ...

... 李智敏等, 2018) ...

2018

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2013

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李智敏, 李文巧, 田勤俭, 等. 2013. 青藏高原东北缘热水-日月山断裂带热水段古地震初步研究[J]. 地球物理学进展, 28(4): 1766—1771.

Based on remote-sensing interpretation, we find that the fault trace is obvious in the image and the rivers are all dextral dislocated cross the fault. The lateral displacements are ranging from 140 m to 940 m. Through the trench excavation, one paleo-seismic event was exposed, which happened in 9645±220 a B.P. Combined with previous published results, we get the recurrence interval of the paleo-earthquake, which is about 3365 a, the dip-silp rate is 0.03 mm/a during the early Holocene. Three paleo-earthquakes have been exposed on Riyue MT.fault so far, which is 9645±220 a B.P,6280±120 a B.P and 2220±360 a B.P respective, the recurrence interval is 3600 a.Because the nearest paleoseismic event is about 2220 a, there is still a long time contrasted to its recurrence interval, but taking into account the uncertainties of paleoseismic events and age of the sample error, We concluded that the seismic disaster on the Reshui segment of the Riyue MT.fault zone is small, but does not rule out the possibility of moderately strong earthquakes.

1. Seismological Bureau of Qinghai Province, Xining 810001, China; 2. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China; 3. Institute of earthquake science, China Earthquake Administration, Beijing 100036, China

通过遥感影像解译和详细的野外填图,获得了热水-日月山断裂带热水断裂段的断错地貌,其水系右旋断错量为140~940 m.沿断裂带的探槽开挖,揭示距今9645±220 a B.P,热水段曾发生一次古地震事件;结合前人的研究结果,认为热水-日月山断裂带热水断裂段上古地震复发间隔约3365 a,全新世以来的倾滑速率为0.03 mm/a.热水-日月山断裂带上已揭露出3次古地震事件,分别为9865±40 a B.P~9425±35 a B.P,6280±120 a B.P 和2220±360 a B.P,复发间隔为3500 a左右,由于该断裂段最近一次古地震事件距今已接近2220年,与其复发间隔3365 a年相比尚有一段时间,但考虑到古地震事件的不确定性和年代样品的误差,初步推断热水-日月山断裂带热水段的地震危险性不大,但不排除有中强地震的可能性.

... 李智敏等, 2013)(图1b) ...

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1998

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冉勇康, 邓起东. 1998. 海原断裂的古地震及特征地震破裂的分级性讨论[J]. 第四纪研究, 18(3): 271—278.

Although the ideology and methodology of paleoearthquake research in China keepup with the advanced world level, there is still a certain insufficiency in some aspects.The main deficiency is that most of the previous work was not sufficient enough toensure the reliability of the obtained paleoearthquake data. For examples, 3-Dbenching has never been used so far to reveal the distribution of displacementproduced by paleoearthquakes along strike-slip fault. In thes paper, we will lay aspecial emphasis on the discussion of paleoseismology based on an exhaustive study.The Haiyuan strike-slip fault on the northeastern margin of Qinghai-Xizang Plateauhas been selected as a case for the study of paleoearthquakes and displacements bymeans of 3-D trenching , while grading on characteristic earthquakes and segments willbe discussied.A trench group had been excavated across the Haiyuan Fault at Gaowanzi village.The bench group consists of 11 trenches, each of which is 2.5-3.5m deep, and wasexcavated in a field of 42m in length and 20-25m in width. The benches have beenlogged on a scale of 1: 20 by using 100cm × 100cm added by 20cm × 20cm grids.The paleoearthquake events revealed by the trenches were discussed in 3-D space.The resultS have been compared with those obtained from other trenches along theHaiyuan Fault in order to get better understanding of the history of paleoseismic activ ity along this fault. Moreover, fault window or Progressive constraining method hasbeen used to compare paleoseismic events in the same segment and to confirm thesegmentation of the fault provided that the geometry of the fault and the displacementproduced by the events had been taken into account.The 3-D benching along Haiyuan Fault at Gaowanzi has revealed 7 Holocene Paleoseismic events (including the M= 8.6 earthquake in 1920). The sinistral displacements produced by the last 5 events have been determined to be 5.6 ± 2.3, 1.5±1．1,1.5 ± 1.2, 2 ± 1, and 7 ± 0.5m from old tO young, respectively . The amountS ofdisplacementS Produced by these events indicates that not all of the events were asstrong as the 1920 earthquake, and only one event was close to the latter . 14 eventscan be recognized when comparing the information obtained from 3-D benching withthat obtained from the other 7 trenches along the Haiyuan Fault . Among them, 3events had ruptured the whole fault (the master segment), while the others justruptured the secondary segments of the fault It shows that there are two grates of thecharacteristic earthquakes occurred on Haiyuan Fault Large characteristic earthquakes(M≥ 8.2) ruptured the whole fault (the master segment) and small characteristic earthquakes (7.5 ≥ M≥ 7) associated with the secondary segments.There are also the glading phenomena of characteristic earthquakes and segmentsalong Altyn Fault and Laohushan -Maomaoshan strike -slip fault except Haiyuan FaultBesides, the grading phenomena are hardly discovered along normal faults. Therefore,we think the grading phenomena of characteristic earthquakes and segments correlated mainly with strike-slip faults.

Institute of Geology, Seismological Bureau of China, Beijing 100029

海原断裂高湾子地点三维探槽揭露了全新世5次事件的位移量。由老至新走滑位移量分别为：5．6±2．3,1．5±1．1,1．5±1．2,2±1和7±0．5m。古地震对比反映出,晚第四纪以来断裂带发生的14次事件中,仅有2～3次事件为贯穿全断裂的破裂事件,说明古地震并不都具有1920年海原大地震的强度。特征地震和段落存在分级性。破裂分级的现象不是孤立的,但多发生在走滑断裂上。

... 冉勇康等, 1998 ...

1998

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2002

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施雅风, 贾玉连, 于革, 等. 2002. 40~30ka BP青藏高原及邻区高温大降水事件的特征、影响及原因探讨[J]. 湖泊科学, 14(1): 1—11.

40-30kaBP相当于末次冰期大间冰阶或海洋氧同位素MIS3晚期.青藏高原在岁差周期夏季高太阳辐射作用下,据古里雅冰芯与若干孢粉记录指示温度比现在高2-4℃,高原及邻区众多大湖的高湖面记录指示大范围降水丰沛.应用Kutzbach水能平衡方程推算了封闭湖泊流域(青海湖、扎布耶/拉果错、阿克塞钦/甜水海)年平均降水可达640mm,560mm,260mm,分别是现代降水的1.7倍,3倍,5倍.高原及邻区包括祁连山以北和云南部分区域在内的大降水对水系河流产生了重大影响.高原内部河湖串联,水系合并;如色林错、班戈错、纳木错串联为高原上最大的内陆水系;若尔盖古湖外流并入黄河水系;长江上游大水在三峡束狭形成强烈旋涡掏蚀成低于海平面的深槽,形成了深槽中、底部的砂砾沉积.这次高温大降水事件是由高太阳辐射导致的由青藏高原高温热低压加强、热带洋面增暖蒸发强烈、南半球越赤道气流增强共同作用而形成的高原特强夏季风,同时极地冰盖迫使西风带南移也可能加强了对高原尤其是西部的降水.H3事件(27kaBP)促进了高温大降水事件的结束,H4事件(35.5kaBP)则可能短期萎缩了夏季风,使高温大降水事件呈现不稳定性特点.

... 青藏高原自湖泊扩张时期以来, 气候变化事件控制了青藏高原东北缘的地貌发育特征(施雅风等, 2002 ...

2002

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2006

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田勤俭, 丁国瑜. 2006. 青藏高原北部第四纪早期断裂活动的新生性变化初步研究[J]. 第四纪研究, 26(1): 32—39.

Haiyuan Fault Zone and Kekexili-East Kunlun Fault Zone are main regional strike slip fault zones in Northern Tibetan Plateau. There is a series of pull-apart basins developed in different periods in the Haiyuan Fault Zone. The Laolongwan Basin developed in Neocene is the largest one. At northeast of the Laolongwan Basin, a series of smaller pull-apart basins are existing. By analyzing the strata and morphostructures at edges of these latest pull-apart basins, we believe that the latest pull-apart basins in the Haiyuan Fault Zone were generated later than 1.6MaB.P., indicating a new tectonic period when a new fault was generated. The direction of the newly generated fault had a counterclockwise angle with the original fault. A series of strong earthquakes occurred along the Kekexili-East Kunlun Fault Zone in Central Tibetan Plateau. Surface rupture of earthquakes indicated a new fault in that zone. Through the study of the new fault trace and morphostructures by earthquake surface rupture investigation and satellite image interpretation, we suggest that the Kekexili-East Kunlun Fault Zone is a zone with many new generated faults, which were generated between 1.1MaB.P. and 0.65MaB.P., and also have counterclockwise angles with the original faults. Beside the Haiyuan Fault Zone and the Kekexili-East Kunlun Fault Zone, many other fault zones in Northeastern Tibet Plateau can be found to have new fault traces. Most of these new fault traces have counterclockwise angle with the original faults. This is consistent with the clockwise rotation of the Tibetan Block. We thus presume that a tectonic event might occur at middle to late Early Pleistocene in Northeast of Tibetan Plateau.In this paper we have attempted to discover the fault activities in order to reveal the characteristics of the regional tectonic event along with the uplifting of the Tibetan Plateau in Early Quaternary, and to accumulate data for study style and distribution of each tectonic event.

Institute of Earthquake Science, China Earthquake Administration, Beijing 100036

关于第四纪早期构造事件的年代学研究取得了大量数据,但对构造事件的表现形式缺乏认识。文章通过对海原断裂带内拉分盆地演化趋势及年代学研究,认为海原断裂带内的最新拉分盆地形成于1.6MaB.P.之后,代表一次新断裂的形成时期,且新断裂走向与先存断裂有一定的逆时针夹角。通过对青藏高原中部可可西里-东昆仑断裂带构造地貌的遥感解译和强震破裂调查,认为可可西里-东昆仑断裂带是一条具有新生性的强震构造带,新断裂形成时期为1.10~0.65MaB.P.之间,其构造带内的新生性断裂走向与先存断裂亦有一定的逆时针方向夹角。两条断裂带具有一致的演化趋势,说明在早更新世中后期存在区域性的构造事件,该事件表现为一系列新生性断裂的产生。

... 田勤俭等, 2000, 2006 ...

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田勤俭, 申旭辉, 丁国瑜, 等. 2000. 海原断裂带内第三纪老龙湾拉分盆地的地质特征[J]. 地震地质, 22(3): 329—336.

A Tertiary pull-apart basin named Laolongwan basin was found in the Haiyuan fault zone. Through interpretation of the satellite image and observations of stratigraphic profiles in the field, stratigraphic sequence, sediment distribution and character of relevant faults in the basin are studied. The Laolongwan basin developed at the largest step area in the Haiyuan fault zone, and the deposition in the Laolongwan basin is bounded by faults. The total thickness of deposition in the basin is about 4600m including boulder rock, gravel-sand rock and sand-mud rock, and breccia rock from the bottom to the top. Strata in the basin discordant contact with various strata outside the basin. Comparing stratigraphic sequence in the basin with regional Tertiary stratigraphical timetable, it is suggested that the Laolongwan basin started in the middle Miocene. Thus, based on above characters, the Laolongwan basin is identified as a Tertiary pull-apart basin in the Haiyuan fault zone. The Laolongwan pull-apart basin provides geological evidence of strike slipping on the northeast edge of Tibet in Tertiary time.

1. Center for Analysis and Prediction, China Seismological Bureau, Beijing 100036; 2. Seismology Institute of Laozhou, China Seismological Bureau, Lanzhou 730000; 3. Seismological Bureau of Niugxia Hui Autouomous Region, Yiuchuan 750001

在海原断裂带内部发现一个第三纪拉分盆地,命名为老龙湾拉分盆地。根据卫片解译结果和野外地质调查,对该盆地内的地层沉积序列、地层分布、相关断裂等特征进行了研究。结果表明,老龙湾拉分盆地发育于海原断裂内的最大斜列部位,盆地沉积受边界断裂控制;盆地内部沉积了巨砾岩、杂砾岩及紫红色-灰绿色泥岩、桔红色角砾岩等地层,最大沉积厚度约4600m。老龙湾盆地内部地层不整合于不同的外围地层之上,根据对盆地内部沉积序列及外围第三系的区域对比,认为盆地沉积开始于中新世中期。由以上特征确定老龙湾盆地为海原断裂带内的第三纪拉分盆地。它为青藏高原东北缘第三纪的走滑断层活动的研究提供了地质证据。

... 田勤俭等, 2000, 2006 ...

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... fp₁和T₁对应于早全新世温暖期向晚全新世干冷期转换的过渡时期(王燕等, 2006 ...

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徐锡伟, 于贵华, 陈桂华, 等. 2007. 青藏高原北部大型走滑断裂带近地表地质变形带特征分析[J]. 地震地质, 29(2): 201—217.

The Altyn Tagh,Kunlun and Haiyuan Faults are three major left-lateral strike-slip faults with high geologic and GPS-derived horizontal slip rates as well as frequent surface-rupturing earthquakes in the northern Tibetan Plateau.There exist local structures,such as pull-apart basins in stepovers and sag ponds,where fine-grained and/or organic interfaulting sediments have been continuously filled and co-seismic faulting traces have been well preserved in those sediments.Trenching across the strike-slip faults and those local structures,stratum-logging of the trench walls and structural-stratigraphic examination can uncover basic features of the permanent and cumulative geologic deformation zone of a strike-slip fault that has experienced several surface-rupturing earthquake cycles.The geologic section of the Banguoba trench 9km east of Old A'kesai Town across the recent traces of the Altyn Tagh Fault records 7 paleoearthquake events with a co-seismic left-lateral slip of 7±1m for the latest event and its cumulative geologic deformation zone is only 8m in width.The geologic section of the western Old A'kesai trench across a pull-apart basin of the Altyn Tagh Fault records at least 4 paleoearthquake events and its permanent and cumulative geologic deformation zone is only 13m in width.The geologic section of the Xidatan trench across the Kunlun Fault reveals 5 paleoearthquake events and their cumulative geologic deformation zones are 12～13m in width.The Maqin trench across a pull-apart of the Kunlun Fault also reveals 5 paleo-earthquake events and most of the structural deformation,about 15m wide,is concentrated in the pull-apart,while the widest structural deformation,including the associated distortion nearby the boundary fault of the pull-apart,is less than 35m.Two trenches excavated across the southern and northern boundary faults of the Songshan pull-apart basin along the Maomaoshan-Laohuashan segment of the Haiyuan Fault show up 6 paleoevents and their permanent geologic deformation zones are less than 10m wide for single boundary fault.Of course,as a extensional jog,the pull-apart basin over a hundred meters wide will experience severe tensional and transtensional surface ruptures during an earthquake,and the pull-apart basin itself may be taken as one part of the permanent geologic deformation zone.Thus,the repeatedly faulting of the Altyn Tagh,Kunlun,and Haiyuan Faults during the past several surface-rupturing earthquake cycles is localized along their strike and the width of their permanent geologic deformation zone for a single strike-slip fault is over 10 meters,but less than 30 meters in general.

1. Institute of Geology, China Earthquake Administration, Beijing 100029, China; 2. Institut de Physique du Globe, 75005 Paris, France; 3. Institute of Tibet Plateau Research, Chinese Academy of Sciences, Beijing 100085, China

阿尔金断裂带、东昆仑断裂带和海原断裂带是青藏高原北部的大型左旋走滑断裂带,具有相对高的地质和GPS滑动速率,地表破裂型地震频发。在阿尔金断裂带阿克塞老城西和半果巴、东昆仑断裂带西大滩和玛沁、海原断裂带松山等地点的探槽地质剖面揭露了这些走滑断裂带累积地质变形带的基本特征。阿尔金断裂带半果巴探槽和阿克塞老城西探槽、东昆仑断裂带西大滩探槽和玛沁探槽揭露出的地质变形带宽度约12m左右;海原断裂带松山拉分盆地边界单条走滑断层地质变形带宽度不足10m,考虑到地震期间拉分盆地可能会出现较严重的变形,则拉分盆地本身也应作为强变形带处理。由此可见,经历过多个地震地表破裂循环的东昆仑断裂带、海原断裂带和阿尔金断裂带其地质变形带的宽度是有限的,具有变形局部化特征。单条走滑断层的地质变形带宽度一般为10余米,比较保守地估计应<30m,走滑断层斜列阶区的地质变形带宽度取决于阶区本身的宽度。

... 徐锡伟等, 2007 ...

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... 于学峰等, 2006) ...

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... 河西走廊地区(袁道阳等, 1997 ...

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... 主断裂两端则形成帚状分叉(袁道阳等, 2003a ...

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袁道阳, 刘小龙, 张培震, 等. 2003 b. 青海热水-日月山断裂带的新活动特征[J]. 地震地质, 25(1): 155—165.

The Reshui-Riyueshan active fault zone lies within the central part of the Qaidam-Qilianshan active block on the northeastern margin of the Qinghai-Tibet Plateau. It is a NNW-trending right-lateral strike-slip active fault zone with reverse components characterized by clear linear features and strong activities. It initiates to the north of Datong River, and extends southward through the Reshui coal mine, running along the eastern side of the NNW-oriented Datongshan and Riyueshan upheaval area, and obliquely connected with Lajishan active fault zone at the pass of Riyueshan Mountain. The fault zone is generally striking N35°W, having a total length of about 183km and a relatively simple geometrical structure. It consists of 4 discontinuous secondary en echelon faults, which are Datong River (F 1-1 ), Reshui (F 1-2 ), Haiyan (F 1-3 ) and Riyueshan (F 1-4 ) Faults, respectively. Extensional zones or pull-apart small basins, such as Ketu basin, were formed at the step-over of these secondary faults. The wide of the step-over is about 2～3km. The Reshui-Riyueshan active fault zone was a compressive reverse fault zone in the early period, and caused the strong compressive deformation of late Cenozoic strata on both side of the fault. Since late Quaternary, the fault zone has become a right lateral strike-slip reverse fault, which has given rise to the formation of micro-morphology represented by right-laterally offset ridges, valleys and terraces. The larger offset may reach up to hundreds meters or more, while the smaller offsets are just about several meters. The right-lateral offset of the first level terrace is about 8～11m, while that of the second level terrace is about 35m. At the same time, there are many fault cliffs and fault scarps developed along the fault zone. The height of the fault scarp at the first level terrace is about 0.5～1m, and the highest one is about 2.8m; at the second level terrace and pluvial mesa, the height of the scarp is about 2.5～3m,with the highest value of about 4～5m. According to the 14C age of the first level terrace of about 3 000a, the horizontal slip rate along the Reshui-Riyueshan Fault zone since late Holocene is estimated to be about 3.16 mm/a, and the vertical slip rate is about 0.83 mm/a. According to the TL age of the second level terrace of about 23.8±1.2ka, the horizontal slip rate along the fault zone since late Pleistocene is estimated to be about 1.47mm/a, and the vertical slip rate is about 0.10～0.21mm/a. Comparatively speaking, the higher the terrace, the stronger the erosion in later period, and hence the larger the uncertainty of the measured offsets. On the contrary, the lower the terrace, the smaller the erosion, and hence the smaller the uncertainty of the measured offset. It is believed, therefore, that the Holocene horizontal slip rate of about 3.16 mm/a, and vertical slip rate of about 0.83 mm/a for the fault zone calculated from the first level terrace are more reliable.

1. Lanzhou Institute of Seismology, China Seismological Bureau, Lanzhou 730000, China; 2. Institute of Geology, China Seismological Bureau, Beijing 100029, China

热水-日月山断裂带是发育在青藏高原东北缘柴达木-祁连活动地块内部的1条重要的NNW向逆-右旋走滑活动断裂带,长约183km.断裂由4条不连续的次级断裂段右阶羽列而成,阶距2～3km左右,在不连续部位形成拉分区.主断裂两端则形成帚状分叉.断裂活动形成了一系列山脊、冲沟和阶地等右旋断错微地貌,其中Ⅰ级阶地右旋断错约8～m,Ⅱ级阶地右旋断错约35m.同时沿断裂带还形成了许多断层陡坎,Ⅰ级阶地或洪积台地上断层陡坎高约0.5～1m,最高达2.8m,Ⅱ级阶地或台地上的断层陡坎高约2.5～3m,最高达4～5m.根据相应的阶地年代,计算得到断裂带全新世以来的平均水平滑动速率为3.16mm/a,垂直滑动速率为0.83mm/a.

... 日月山断裂作为一条重要的块体内部断裂, 其几何分段和地貌年龄研究取得的成果(袁道阳等, 2003b ...

... 0ka, 可相互进行对比(袁道阳等, 2003b ...

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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.

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。

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... 张培震等, 2006, 2013) ...

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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.

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。

... 张培震等, 2006, 2013) ...

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... 郑文俊等,2004, 2009, 2012 ...

... 郑文俊, 2009), 但关于块体内部活动断裂的构造变形量和构造变形演化过程的研究却相对缺乏, 如针对南祁连地区的日月山断裂、鄂拉山断裂以及拉脊山断裂等的相关研究较少, 限制了地学工作者对该块体内部变形机制的认识 ...

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郑文俊, 袁道阳, 何文贵. 2004. 祁连山东段天桥沟-黄羊川断裂古地震活动习性研究[J]. 地震地质, 26(4): 645—657.

The Tianqiaogou Huangyangchuan Fault (called also Gulang Fault) lies to the east of Lenglongling,the highest peak on the eastern section of the Qilianshan Mountains. It is one of the important active faults in eastern Qilianshan. From west to east,the fault is about 86km long,initiating from Hongyaoxian,extending eastward along Tainqiaogou,Qianjin,Guanjiatai,and Huangyangchuan villages,and ending at Jiapigou. The western segment of the fault is NWW-trending,the middle is nearly E-W-trending and the eastern is NEE-trending. Among them,the middle segment is convex slightly to the south. The fault is basically continuous,except that a small step-over exists near Guanjiatai village,dividing the fault into two sub-segments:the Tianqiaogou sub-segment in the west and the Huangyangchuan sub-segment in the east. Field investigation revealed that offset landforms are well developed along the fault,such as offset gully,fault scarp,sag pond,offset terrace and alluvial fans. All the offset landforms indicate that the fault was dominated by left lateral strike-slip with a component of normal faulting. Tracing along the fault and trenching across 6 typical offset landforms revealed the evidence of Holocene activities and several palaeo earthquakes along the fault. By the use of progressive constraining method,7 Holocene palaeo-earthquakes and one historic earthquake are identified. The occurrence time of these events are determined to be 10,743±342a BP (Event Ⅰ),9038±39a BP (Event Ⅱ),6910±438a BP (Event Ⅲ),4847±185a BP (Event Ⅳ),3562±190a BP (Event Ⅴ),2476±194a BP (Event Ⅵ),1505±253a BP (Event Ⅶ) and 1927AD (Event Ⅷ,possibly the Gulang earthquake). The distribution and recurrence behavior of strong earthquakes along the fault show a distinct linearity and sub-periodical recurrence,for which the linear regression equation of event-time sequence is T i = 1516i-11734 . Moreover,during field investigation we found new evidence indicating that surface rupture occurred along the Tianqiaogou-Huangyangchuan fault during the Gulang M S 8.0 in 1927.

1. Lanzhou Base of Institute of Earthquake Science, China Earthquake Administration, Lanzhou 730000, China; 2. Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China

天桥沟-黄羊川断裂位于祁连山东段主峰冷龙岭以东,是祁连山东段的重要活动断裂之一。该断裂以关家台为界分为东西2段,全新世以来均有过明显的活动。沿断裂开挖了6个古地震探槽,通过综合对比得到了该断裂全新世以来的7次古地震事件和1次历史地震事件,其年代分别为事件Ⅰ(10743±343)aBP,事件Ⅱ(9038±39)aBP,事件Ⅲ(7050±577)aBP,事件Ⅳ(4847±185)aBP,事件Ⅴ(3562±190)aBP,事件Ⅵ(2476±194)aBP,事件Ⅶ(1505±253)aBP,事件Ⅷ为1927年古浪8级大地震。这表明该断裂可能也参与了1927年古浪8级地震的活动。各次古地震事件在时空分布上相对较均匀,大致具有准周期复发的特征。

... 郑文俊等,2004, 2009, 2012 ...

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郑文俊, 张培震, 袁道阳, 等. 2009. GPS观测及断裂晚第四纪滑动速率所反映的青藏高原北部变形[J]. 地球物理学报, 52(10): 2491—2508.

GPS measurements and late Quaternary fault slip rates reveal the kinematic pattern of outward growth of the northern margin of the Tibetan Plateau. Base on the geologic data and GPS velocity slip rates of major boundary faults are less than 10 mm/a including the Altyn-Tagh fault and Haiyuan- Qilianshan fault. The distributions of slip rates along the two major faults show constant slip rate along their middle portion and decrease toward their ends. For example, the left-lateral slip rates on the central segment of Altyn-Tagh Fault appear to be in the range of 8～12 mm/a, but decreases eastward to only 1～2 mm/a near 97°E. On the Haiyuan-Qilianshan fault, slip rates are 1～2 mm/a in its western segment, and increase to 4～5 mm/a in its eastern and middle segments, and then decrease to 1～3 mm/a near its eastern end near the Liupan Shan. This kind of slip distribution suggests that almost all motion along a strike-slip fault is accommodated by crustal shortening or convergence near the ends of the strike-slip fault. The crustal shortening across the Qilian Shan absorbs strike-slip along the Altyn Tagh fault. The convergence in Liupan Shan accommodates left-lateral slip along the Qilian-Haiyuan fault. Our studies show that tectonic deformation occurred mainly within the northern Tibetan Plateau, and that the rule of strike slip faulting has been reconciling differences of crustal shortening or crustal thickening rather than extruding crustal blocks out of the plateau interior.

1 State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China 2 Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China

断裂晚第四纪滑动速率及现今GPS观测揭示了青藏高原向北扩展与高原边缘隆升的运动特征.主要断裂晚第四纪滑动速率及跨断裂GPS应变速率的结果表明，青藏高原北部边缘的断裂以低滑动速率（＜10 mm/a）为主，特别是两条边界断裂：阿尔金断裂和海原—祁连山断裂.两条主要边界断裂上的滑动速率分布显示了断裂间滑动速率转换及调整特征.阿尔金断裂自95°E以西的8～12 mm/a稳定滑动速率，向东逐渐降低到最东端的约1～2 mm/a，而海原断裂自哈拉湖一带开始发育后滑动速率为1～2 mm/a，到祁连一带（101°E以东）增大到相对稳定的4～5 mm/a，直到过海原后转向六盘山一带，滑动速率降低到1～3 mm/a，甚至更低.滑动速率的变化及分布特征显示，阿尔金断裂滑动主要是通过祁连山内部隆起及两侧新生代盆地变形引起的缩短来吸收的，海原—祁连山断裂的低滑动速率及沿断裂运动学特征表明断裂尾端的陇西盆地变形及六盘山的隆起是断裂左旋走滑速率的主要吸收方式.这一变形特征表明，青藏高原北部边缘的变形模式是一种分布式的连续变形，变形发生自高原内部，边界断裂的走滑被高原内部变形所吸收.

2009

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2011

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... Yuan et al ...

... 由于青藏块体向NE扩展, 致使NWW向的区域主边界断裂发生左旋走滑, 而夹持于其间的NNW向日月山断裂被剪切压扁, 其运动性质为右旋走滑兼逆冲作用(Yuan et al ...

... Yuan et al ...

... NW向大型主边界断裂与夹于其间的日月山断裂和鄂拉山断裂为代表的块体内部NNW向断裂可能构成了1组共轭构造(Yuan et al ...

2016

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... Fossen et al ...

2005

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... 针对断层侧向长度增长过程中断层表现的形态以及位移量和长度之间的关系所进行的研究也取得了丰富的成果(Kim et al ...

... (3)断层位移分布曲线极值偏移方向受应变场叠加影响, 所在位置指示了应变集中和应力积累的位置(Kim et al ...

1991

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... 4)两侧小型断层被新生的连接断层贯穿成一条大规模的断层, 在连接位置存在位移极小值(图2d), 随时间增加, 连接位置位移增长至与两侧相同, 随后, 断层连接进入下一次循环(Peacock et al ...

2017

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... Peacock et al ...

2013