共查询到19条相似文献，搜索用时 93 毫秒
1.
柯坪塔格前缘断裂东段是柯坪推覆构造系前缘的一条活动断裂,野外调查获得了其晚第四纪错断洪积扇、冲沟阶地面的证据,实测了变形地貌面上的断层陡坎,分析了断层的形变量,通过采样测年估算了断层的缩短速率。由7个观测点的断层陡坎剖面测量,计算了观测点处断层的水平缩短速率,结果表明,断裂弧顶部位的五道班、三间房以西及其大山口道班附近,断层错断了Ⅰ级和Ⅱ级洪积扇(阶地)。断层在这些地点最新活动强烈,水平缩短平均速率全新世以来为0·35~0·44mm/a,更新世晚期末以来为0·16~0·30mm/a,而在非弧顶部位的巴楚磷矿、三岔口以北及大山口北断层只错断了更新世晚期Ⅲ级洪积扇,且水平缩短速率较小,断层水平缩短平均速率更新世晚期以来为0·05~0·07mm/a 相似文献
2.
库车坳陷是南天山中段新构造运动异常强烈的地区,发育4排近EW向展布的逆断裂-背斜带。通过野外实地考察及前人资料分析,认为该区晚第四纪以来的构造变形主要集中于喀桑托开逆断裂-背斜带、秋里塔格逆断裂-背斜带和最南缘的亚肯逆断裂-背斜带之上,而且不同构造带之间的变形方式存在较大差异。作者利用全站仪(total station)对上述构造带的变形地貌进行了精确测量,并结合年代学分析,得到喀桑托开逆断裂-背斜的地壳缩短速率为1·0~2·0mm/a,秋里塔格逆断裂-背斜带的地壳缩短速率为2·5~3·0mm/a,亚肯盲逆断裂-背斜的地壳缩短速率为1·5~2·0mm/a。晚第四纪以来,库车坳陷SN向总的地壳缩短速率不<5·0~7·0mm/a 相似文献
3.
柯坪推覆构造系是西南天山前陆推覆构造的重要组成部分。文中试图通过对柯坪推覆构造区的影像解译和野外观察、断错地貌的实测和探槽开挖,探讨柯坪塔格山前断裂东段晚第四纪以来的古地震活动。在三岔口以西的五道班—三间房一带和三岔口以东的大山口道班一带,除现代洪积扇外,明显可见2期保存较完整的洪积扇被断错。五道班—三间房地段的3个探槽揭露出了晚更新世末期以来该破裂段发生的4次事件,其参考年代为:距今22、14、6·5和4·4ka;重复间隔时间约为:8、7和2ka左右。间隔时间长的事件垂直位移量约1~1·2m,缩短量约1·3~1·4m;间隔时间短的事件,垂直位移量0·20~0·30m,缩短量0·6~0·7m。大山口道班段探槽揭露出了晚更新世末期以来的2次事件,分别发生在稍早于距今13ka和稍晚于距今6ka。重复间隔时间约7ka。同震垂直位移量约50cm,缩短量130cm左右 相似文献
4.
《内陆地震》2016,(2)
博格达推覆构造,由南向北发育3~4排活动断裂,活动性逐渐向北迁移,最新活动主要集中在前缘的阜康断裂及北三台断裂上。阜康断裂上盘在二工河一带为单斜岩层,具有断弯褶皱的特征,通过测量阶地拔河高度、阶地基座岩层的产状以及阶地年代数据,应用断弯褶皱变形的关系式得到了断层沿断层面滑动速率为0.8 mm/a;北三台断裂发育在断层扩展褶皱北三台背斜北翼,利用阶地剩余面积及褶皱滑脱面埋深,计算得到北三台背斜晚更新世晚期以来的缩短速率在0.5~0.9mm/a之间。综合得到博格达北麓晚第四纪地壳缩短速率为1.3~1.7 mm/a,考虑到埋藏地貌面的变形量,估计博格达北麓晚第四纪以来南北向总的地壳缩短速率在1.5~2.0 mm/a之间。 相似文献
5.
《国际地震动态》2017,(9)
天山是远离板块边界的陆内造山带,特点是构造变形复杂强烈,强震多发。天山南北向的变形速率约为20mm/a,约为印度板块与欧亚板块汇聚速率的一半左右,这一变形量是如何被天山吸收的,天山的构造变形又是如何进行的,其构造样式如何?这些关键性问题目前仍存在较大的争论。天山地区主要发育有3组构造带,最显著的是位于南北两侧山前与山体近乎平行的逆断层—褶皱带,同时,在山体内部还发育有一系列NW向的右旋走滑断裂和NEE向的左旋走滑断裂,这些断裂共同控制了天山的新生代构造变形。目前,对于天山山前的逆断裂系统晚第四纪变形特征和滑动速率等方面研究非常丰富,对天山内部NW向的右旋走滑断裂晚第四纪活动特征也有一些定量数据,而对NEE向断裂晚第四纪以来的活动特征目前尚处空白状态。本文以迈丹断裂为切入点,通过对该断裂晚第四纪以来的运动学特征、滑动速率和古地震活动特征等资料的详细研究,获得西南天山地区NEE向断裂晚第四纪活动参数,同时,通过收集和补充调查天山其他主要活动断裂晚第四纪以来的运动特征,完善天山活动断裂几何学和运动学图像;结合已有研究资料、地震活动特征和GPS数据,研究天山内部不同方向、不同运动性质的断裂的活动特征,分析天山这些断裂在天山的构造变形中发挥了怎样的作用,在此基础上进一步研究天山地区的构造变形样式及其与地震的关系。本文得到的主要认识有:迈丹断裂东段控制的阿合奇谷地内发育有多级晚第四纪地貌面,利用光释光、10Be暴露年龄以及14C等方法对玉山古溪两岸的阶地年龄进行了限定,并与气候变化序列进行了比对,得到阶地的废弃形成发生在间冰期或者冰期—间冰期的转换阶段。玉山古溪T6阶地(~20ka)之前,河流平均下切速率与迈丹断裂的活动速率基本一致,表明晚更新世晚期之前,河流的下切与阶地的形成主要受迈丹断裂活动影响,是构造隆升导致的河流快速下切。~20ka之后河流的下切速率开始增大,至全新世中晚期,河流下切速率甚至达到~12mm/a,远远大于断裂的活动速率,表明晚更新世末期以来,河流的下切与阶地的形成主要受气候因素驱动。全新世以来河流下切速率的快速增大,很可能是由于全新世期间气候快速波动造成的。迈丹断裂是一条全新世活动断裂,该断裂晚第四纪以来,以逆冲兼左旋走滑为主,通过精细测量被断错的晚第四纪地貌面和年代学测定,得到断裂的逆冲滑动速率为(1.24±0.20)mm/a,左旋走滑速率为(1.74±0.61)mm/a。迈丹断裂晚第四纪期间发生过多期断错地表的古地震事件,古地震平均复发间隔为3370~4265a,断裂最新一次古地震事件发生在1.76ka之后。迈丹断裂是柯坪推覆构造的根部断裂,该断裂晚第四纪以来发生过多次断错地表的强震事件。古地震研究表明,推覆体前缘的柯坪断裂晚第四纪以来也发生过多期古地震事件,而且两条构造上古地震事件的发生年代很接近,尽管我们并不能确定迈丹断裂最新一次古地震事件是否与柯坪塔格断裂上的是否为同一次事件,但这一现象反映该地区地震破裂存在两种可能:(1)迈丹断裂与柯坪塔格断裂上最新一次古地震事件是同一次事件,这表明迈丹断裂与柯坪塔格断裂具有级联破裂的特征;(2)迈丹断裂上最新一次古地震事件与柯坪塔格断裂上的不是同一期事件,分别单独破裂,虽然两条断裂上的古地震事件不是同期破裂,但均发生在~1.7ka之后,时间间隔不长,表明柯坪推覆构造根部的迈丹断裂和前缘的柯坪塔格断裂之间可能存在相互的影响或关联,柯坪地区的强震活动具有丛集发生的特征。迈丹断裂晚第四纪活动的发现,表明西南天山柯坪推覆构造与天山其他地区的推覆构造变形模式不同,推覆体最前缘的柯坪断裂活动强烈,而根部断裂晚第四纪以来也有很强的活动,断裂的新活动并没有完全迁移到推覆体前缘的新生构造带上,这可能是一种无序或反序的构造变形模式。西南天山地区的左旋走滑运动主要发生在推覆体根部的迈丹断裂上,推覆体前缘的逆断裂—背斜以逆冲运动为主,没有明显的走滑运动。GPS资料表明,普昌断裂以西的地区,应变没有完全闭锁集中在根部的迈丹断裂上,一部分应变通过滑脱面传递到前缘的逆断裂-背斜带上;在柯坪推覆构造的东部地区,从根部的迈丹断裂至前缘的柯坪塔格断裂可能是一个孕震体系,震间的形变主要在推覆体根部的构造上闭锁,前缘构造基本没有明显变形,这可能是柯坪推覆构造东西两侧中小地震活动存在明显差异的主要原因。西南天山还发育有两条NEE走向的断裂,通过变形地貌测量与年代学测定得到那拉提断裂晚第四纪以来以左旋逆冲运动为主,断裂逆冲速率~2.1 mm/a,左旋走滑速率为~2.5mm/a;克敏断裂也是一条左旋走滑断裂,断裂的左旋走滑速率为~1.5mm/a。西南天山3条NEE向的断裂带吸收了~6mm/a的左旋走滑运动,与塔里木斜向俯冲造成的左旋走滑运动量基本一致,这表明塔里木斜向俯冲造成的左旋走滑运动在西南天山地区基本被分解吸收。西南天山地区吸收了塔里木向天山俯冲汇聚绝大部分的压缩速率和左旋剪切运动,挤压缩短在山体内部和山前的新生褶皱带上均有分配,左旋剪切则主要发生在天山内部高角度的边界断裂上,整个西南天山构成了一个大型的花状构造。在天山南北两侧,构造变形以逆断层为代表的地壳缩短和增厚为特征,而天山内部则为一个大型的剪切带,同时还具有明显的逆冲运动。天山地区主要存在两组走滑断裂,一是NEE向的左旋走滑构造,另一组是NW-NWW向的右旋走滑断裂,这两组断裂主要发育在天山内部,但这些断裂共同调节了山体内部的走滑剪切运动,山体内部高角度的走滑逆冲断裂与山前低倾角的逆冲断裂系共同组成了天山构造变形图像。天山地区的压缩变形主要分布在天山南北两侧的山前地区,而天山内部的活动断裂则具有明显的走滑分量,在剖面上,整个天山形成了一个大型的花状构造。尽管天山整体的构造变形为西强东弱,不同地区变形强度和幅度差异较大,但是天山南北和东西两侧的构造变形样式还是基本对称的。受塔里木块体向北的挤压作用,西南天山地区总体走向为NEE向,南天山东段整体则呈NWW走向,与塔里木与南天山的分界断裂在形态上构成一个"三角形"向北楔入。整个西南天山内部是一个大型的左旋剪切带,南天山东段整体为右旋走滑性质,塔里木和南天山之间的边界断裂以逆冲运动为主。在天山北部受到刚性准噶尔地块阻挡的作用下,北天山西段构造线整体NW-NWW向,而90°E以东的北天山地区构造线整体为NEE走向,与近东西走向的准噶尔与北天山的分界断裂在形态上构成一个倒"三角形"向南楔入。北天山西段右旋走滑性质的博—阿断裂和喀什河断裂所围限的楔形块体整体向西运动,北天山东段NEE向的左旋走滑断裂构成了倒"三角楔"的东边界,准噶尔与北天山的分界逆冲断裂带是"三角楔"的底界。在近南北向的挤压应力下,天山的构造变形整体以压缩变形为主,山体内部发育的一系列走滑构造带表明,天山在东西方向上还存在一定的侧向挤出,这些走滑断裂调节了天山不同地区压缩量的差异。地质数据和GPS资料均证实,天山地区逆冲运动量要明显大于走滑分量,山体内部走滑断裂所控制的块体虽然存在向东西两侧的侧向挤出,但与南北向最大达~18mm/a的压缩速率相比,变形速率不高,侧向挤出幅度有限。 相似文献
6.
南天山柯坪塔格推覆体前缘断裂活动性质及速率 总被引：1，自引：0，他引：1
柯坪塔格推覆体位于天山西南麓,由多排NEE—EW向的褶皱-逆断裂带组成。文中介绍了皮羌—巴楚磷矿以西3排褶皱-逆断裂带前缘断裂的活动性质及速率。新获资料表明,各排褶皱-逆断裂带前缘皆由多条断裂构成,都具典型的逆断层性质。其中最新活动断裂位于褶皱-逆断裂带的最前缘,活动时代为晚更新世—全新世。它们切割冲沟T0、T1、T2、T3阶地堆积,形成不同高度的断层陡坎。根据陡坎剖面测量和年龄样品测试,求得T0面形成以来断裂的垂直位移量、位移速率、地壳缩短量和缩短速率分别是0.9～1.1m、0.53～0.65mm/a、1.93～2.56m和1.14～1.52mm/a;T1面形成以来分别是1.4～1.8m、0.36～0.46mm/a、3.00～3.86m和0.77～0.99mm/a;T2面形成以来分别是2.1～3m、0.31～0.45mm/a、4.50～6.98m和0.67～1.04mm/a;T3面形成以来分别是3.4～4.2m、0.28～0.35mm/a、7.29～9.22m和0.61～0.77mm/a。根据T0面形成以来的缩短量和缩短速率,计算柯坪塔格推覆体约1.7ka以来总的地壳缩短量是9.65～12.80m,缩短速率 相似文献
7.
西南天山迈丹断裂东段晚第四纪活动的发现及构造意义 总被引：1，自引：0，他引：1
利用详细的遥感影像解译、实地调查、探槽开挖以及释光年代学测定的方法对西南天山山前的迈丹断裂东段进行研究,获得了该断裂晚第四纪以来活动的可靠证据。迈丹断裂东段是一条由多条次级断裂组成的复杂断裂带,最大宽度可达17km,晚第四纪以来的活动断错了山前各级地貌面和阶地。探槽开挖表明,断裂在全新世期间曾发生过断错地表的强震事件,造成的垂直位错量在2m以上。迈丹断裂晚第四纪以来活动表明,西南天山地区的构造变形并不完全集中在推覆体前缘新生的逆断裂-背斜带上,天山根部断裂也吸收了一部分构造变形。这一构造变形模式与已知的北天山前展式的构造变形样式具有明显差异,柯坪推覆体并不完全遵从断裂新活动不断向盆地方向扩展的特点,推覆体前缘新生断裂和根部断裂都有较强的活动,可能是一种无序或反序的构造变形样式。此类构造,其发震构造模型的建立及强震危险性预测给我们带来新的挑战。 相似文献
8.
安宁河断裂紫马跨一带晚第四纪地貌变形与断层位移速率 总被引：7，自引：6，他引：1
紫马跨一带是安宁河断裂北段晚第四纪断错地层地貌序列保存最好的地区,通过数字影像分析、全站仪实测和探槽开挖,对该地点断错现象进行细致研究,获得了晚全新世以来的左旋位移速率为6·2mm/a,垂直位移速率1·4mm/a;距今约10ka以来的平均左旋位移速率3·6~4·0mm/a,垂直位移速率约为1·1mm/a;距今约20ka以来的左旋位移速率为3·8~4·2mm/a,垂直位移速率最小为0·9mm/a。断层水平和垂直位移速率的比例约为4∶1。断层位移速率在时间分布上的变化与古地震研究的丛集复发特征有较好的一致性,反映断裂的活动强度存在强弱活动的交替现象 相似文献
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柯坪逆冲推覆构造带是西南天山山前晚新生代以来形成的活动逆断裂-褶皱带,由5~6排近平行的弧形褶皱带组成,出露地层为寒武系—第四系。背斜形态多为复式箱状背斜和不对称的斜歪背斜,分别与断层弯曲背斜和断层扩展背斜的几何形态一致。地震勘探资料显示,各褶皱带前缘活动逆断裂在深部归并于统一的、由寒武系中的石膏层组成的滑脱面。滑脱面深度具有南浅北深、东浅西深的特点,皮羌断裂西侧滑脱面深度约为9km,东侧滑脱面深度为5km。在柯坪逆冲推覆构造中部的皮羌断裂东西两侧各5km和8km的位置,以断层弯曲褶皱和断层扩展褶皱构造模型为指导,用线长平衡的方法完成了2条长度分别为78km和73km的平衡地质剖面,恢复到变形前的形态后计算出这2条剖面上的地壳缩短量分别为40km和45km,缩短率为33%和37%。由于对柯坪逆冲推覆构造开始形成时间的证据较少,所以要计算长期的缩短速率是比较困难的。对比天山南麓库车活动逆断裂-褶皱带的形成时代,以及柯坪逆冲推覆构造与印干断裂的关系,认为柯坪逆冲推覆构造形成于第四纪早期的西域砾岩沉积阶段,按距今2.5Ma计算,柯坪逆冲推覆构造的地壳缩短速率是15.4~17.3mm/a 相似文献
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龙门山中南段前陆区是青藏高原东缘唯一发育新生代薄皮构造与沉积盆地的地段，研究其最新构造变形样式有助于深入理解青藏高原向东扩展的构造机理.论文通过青衣江河流阶地测量与古青衣江洪积扇形态重建，研究了龙门山南段前陆区晚第四纪活动构造格局及其活动性，取得了如下认识：（1）青衣江河流阶地纵剖面显示，龙门山南段前陆地区晚第四纪变形主要为褶皱作用，总体地壳缩短速率为2.5~3.9 mm·a-1，远大于山区冲断带0.48~0.77 mm·a-1的地壳缩短速率，地壳缩短主要由前陆地区吸收；（2）青衣江古洪积扇错断变形显示，龙门山南段前陆区活动构造表现为北西—南东向地壳缩短与近东西向的地壳缩短的叠加作用，两者分别受控于巴颜喀拉块体南东向推挤作用与川滇块体向东推挤作用；（3）自中新世初川滇块体向南东挤出，四川盆地西南角起到分流青藏高原物质的作用，其西南侧物质通过鲜水河—小江断裂带的左旋错动向南东方向分流，其西北侧物质通过龙门山断裂带的右旋错动向北东方向分流，迎面受到了最大的推挤作用，进而向前陆扩展形成了薄皮褶皱构造带. 相似文献
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研究天山地区活动逆冲断裂、褶皱对于认识整个天山再生造山带的隆升和地震危险性评估具有重要意义。以天山北麓博乐盆地南缘库松木楔克断裂东段勒塔干褶皱为研究对象,通过无人机航拍提取高精度DEM和野外实地调查结果,将勒塔干背斜东部迪里克河附近的洪积扇分为5期,从新到老分别为T1、T2、T3、T4、T5。其中,T4洪积扇完整记录了褶皱的变形历史,其后翼褶皱陡坎高度为（8.1±0.6）m。自T4洪积扇废弃以来,勒塔干断层的滑移量为（33.0±2.6）m。T3洪积扇仅发育在迪里克河出水口处,即勒塔干背斜北侧,（16.9±0.2）m的断层陡坎高度揭示了自T3洪积扇废弃以来,控制背斜形成的逆断层发生了21.4～21.7 m的滑动。通过与相邻地区洪积扇期次进行对比,认为T4洪积扇的废弃年龄为（74.01±6.14）ka,勒塔干背斜下断坡晚第四纪滑动速率为（0.45±0.05）mm/a,勒塔干褶皱晚第四纪地壳缩短速率为（0.37±0.04）mm/a。 相似文献
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DONG Jin-yuan LI Chuan-you ZHENG Wen-jun LI Tao LI Xin-nan ZHANG Pei-zhen REN Guang-xue DONG Shao-peng LIU Jin-rui 《地震地质》2019,41(2):341-362
With the continuous collision of the India and Eurasia plate in Cenozoic, the Qilian Shan began to uplift strongly from 12Ma to 10Ma. Nowadays, Qilian Shan is still uplifting and expanding. In the northern part of Qilian Shan, tectonic activity extends to Hexi Corridor Basin, and has affected Alashan area. In the southern part of Qilian Shan, tectonic activity extends to Qaidam Basin, forming a series of thrust faults in the northern margin of Qaidam Basin and a series of fold deformations in the basin. The southern Zongwulong Shan Fault is located in the northeastern margin of Qaidam Basin, it is the boundary thrust fault between the southern margin of Qilian Shan and Qaidam Basin. GPS studies show that the total crustal shortening rate across the Qilian Shan is 5~8mm/a, which absorbs 20% of the convergence rate of the Indian-Eurasian plate. Concerning how the strain is distributed on individual fault in the Qilian Shan, previous studies mainly focused on the northern margin of the Qilian Shan and the Hexi Corridor Basin, while the study on the southern margin of the Qilian Shan was relatively weak. Therefore, the study of late Quaternary activity of southern Zongwulong Shan Fault in southern margin of Qilian Shan is of great significance to understand the strain distribution pattern in Qilian Shan and the propagation of the fault to the interior of Qaidam Basin. At the same time, because of the strong tectonic activity, the northern margin of Qaidam Basin is also a seismic-prone area. Determining the fault slip rate is also helpful to better understand the movement behaviors of faults and seismic risk assessment.Through remote sensing image interpretation and field geological survey, combined with GPS topographic profiling, cosmogenic nuclides and optically stimulated luminescence dating, we carried out a detailed study at Baijingtu site and Xujixiang site on the southern Zongwulong Shan Fault. The results show that the southern Zongwulong Shan Fault is a Holocene reverse fault, which faulted a series of piedmont alluvial fans and formed a series of fault scarps.The 43ka, 20ka and 11ka ages of the alluvial fan surfaces in this area can be well compared with the ages of terraces and alluvial fan surfaces in the northeastern margin of Tibetan Plateau, and its formation is mainly controlled by climatic factors. Based on the vertical dislocations of the alluvial fans in different periods in Baijingtu and Xujixiang areas, the average vertical slip rate of the southern Zongwulong Shan Fault since late Quaternary is(0.41±0.05)mm/a, and the average horizontal shortening rate is 0.47~0.80mm/a, accounting for about 10% of the crustal shortening in Qilian Shan. These results are helpful to further understand the strain distribution model in Qilian Shan and the tectonic deformation mechanism in the northern margin of Qaidam Basin. The deformation mechanism of the northern Qaidam Basin fault zone, which is composed of the southern Zongwulong Shan Fault, is rather complicated, and it is not a simple piggy-back thrusting style. These faults jointly control the tectonic activity characteristics of the northern Qaidam Basin. 相似文献
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龙门山逆冲推覆构造带中段山前断裂的存在和最新活动时代一直是个争论的问题.石油地震探测资料和浅层地震剖面揭示该断裂的存在,并断错了第四系;野外调查表明,龙门山中段山前存在明显的线性地貌特征,山前断裂断错晚了更新世晚期的洪积台地;探槽剖面揭示距今约1500 a之前在山前断裂上曾发生过一次地表破裂型事件,而该断裂未来具备发生强震的潜势.断错地貌的差分GPS测量和年代学分析显示山前断裂晚第四纪垂直滑动速率大于0.36 mm/a,其与龙门山中段主干断裂活动强度相当,说明龙门山山前断裂在龙门山逆冲推覆构造带的变形中也承担着重要的作用.该研究不仅能为成都平原的地震危险性评价提供基础资料,也有助于全面理解青藏高原东缘的隆升机制. 相似文献
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A PRELIMINARY STUDY ABOUT SLIP RATE OF MIDDLE SEGMENT OF THE NORTHERN QILIAN THRUST FAULT ZONE SINCE LATE QUATERNARY 
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下载免费PDF全文 The Fodongmiao-Hongyazi Fault belongs to the forward thrust fault of the middle segment of northern Qilian Shan overthrust fault zone, and it is also the boundary between the Qilian Shan and Jiudong Basin. Accurately-constrained fault slip rate is crucial for understanding the present-day tectonic deformation mechanism and regional seismic hazard in Tibet plateau. In this paper, we focus on the Shiyangjuan site in the western section of the fault and the Fenglehe site in the middle part of the fault. Combining geomorphic mapping, topographic surveys of the deformed terrace surfaces, optically stimulated luminescence (OSL) dating, terrestrial cosmogenic nuclide dating and radiocarbon (14C) dating methods, we obtained the average vertical slip rate and shortening rate of the fault, which are ~1.1mm/a and 0.9~1.3mm/a, respectively. In addition, decadal GPS velocity profile across the Qilian Shan and Jiudong Basin shows a basin shortening rate of~1.4mm/a, which is consistent with geological shortening rates. Blind fault or other structural deformation in the Jiudong Basin may accommodate part of crustal shortening. Overall crustal shortening rate of the Jiudong Basin accounts for about 1/5 of shortening rate of the Qilian Shan. The seismic activity of the forward thrust zone of Tibetan plateau propagating northeastward is still high. 相似文献
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THRUST OF THE SOUTHERN LONGMENSHAN FAULT IN THE LATE QUATERNARY REVEALED BY RIVER LANDFORMS 下载免费PDF全文
下载免费PDF全文 The Longmenshan fault zone is divided into three sections from south to north in the geometric structure. The middle and northern segments are mainly composed of three thrust faults, where the deformation of foreland is weak. The geometric structure of the southern segment is more complex, which is composed of six fault branches, where the foreland tectonic deformation is very strong. The Wenchuan MS8.0 earthquake occurred in the middle of the Longmenshan in 2008, activating the bifurcation of two branches, the Yingxiu-Beichuan and the Guixian-Jiangyou faults. In 2013, the Lushan MS7.0 earthquake occurred in the southern Longmenshan, whose seismogenic structure was considered to be a blind fault. After the Lushan earthquake, the seismic hazard in the southern Longmenshan has been widely concerned.
At present, the studies on active tectonics in the southern Longmenshan are limited to the Dachuan-Shuangshi and the Yanjing-Wulong faults. The Qingyi River, which flows across the southern Longmenshan, facilitates to study fault slip by the deformation of river terraces. Based on satellite imagery and high-resolution DEM analysis, we measured the fluvial terraces along the Qingyi river in detail. During the measurement, the Sichuan network GPS system (SCGNSS)was employed to achieve a precision of centimeter grade. Besides, the optical luminescence dating (OSL)method was employed to date the terraces' ages. And the late Quaternary activities of the six branch faults in the southern Longmen Shan were further analyzed.
The Gengda-Longdong, Yanjing-Wulong and the Xiao Guanzi faults (west branch of the Dachuan-Shuangshi fault)all show thrust slip and displaced the terrace T2. Their average vertical slip rates in the late Quaternary are 0.21-0.30mm/a, 0.12-0.21mm/a and 0.10-0.12mm/a, respectively. Since the Late Quaternary, vertical slip of the east branch of the Dachuan-Shuangshi fault was not obvious, and the arc-like Jintang tectonic belt was not active. Crustal shortening rate of the southern Longmenshan thrust fault zone in the late Quaternary is 0.48-0.77mm/a, which equals about half of the middle segment of the Longmenshan. Based on the previous study on the tectonic deformation of the foreland, we consider that the foreland fold belt in the southern Longmenshan area has absorbed more than half of the crustal shortening. The three major branch faults in the southern Longmenshan are active in the late Quaternary, which have risk of major earthquakes. 相似文献
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HA Guang-hao WU Zhong-hai MA Feng-shan ZENG Qing-li ZHANG Lu-qing GAI Hai-long 《地震地质》2019,41(2):436-446
In the interior of the Tibetan Plateau, the active tectonics are primarily marked by conjugate strike slip faults and north-trending rifts, which represent the E-W extension since late Cenozoic of the plateau. The conjugate faults are mainly composed of NE-trending left-lateral strike-slip faults in Qiangtang terrane and NW-trending right-lateral strike-slip faults in Lhasa terrane. While, the rifts mainly strike N, NNW and NNE within southern Tibet. However, it is still a debate on the deformational style and specific adjustment mechanism of E-W extension. One of key reasons causing this debate is the lack of detailed investigation of these active faults, especially within the northwestern plateau. Recently, we found a 20km long, NNW-trending active fault at Bero Zeco in northwestern Tibet. This fault is presented as fault sag ponds, channel offsets and fault scarps. Displacement of channels and geomorphic features suggested that the Bero Zeco Fault(BZF)is a dextral strike-slip fault with a small amount of normal slip component, which may result from the E-W extensional deformation in the interior of Tibet. BZF strikes N330°~340°W, as shown on the satellite image. The main Quaternary strata in the studied area are two stages alluvial fans around the Bero Zeco. From the satellite images, the old alluvial fans were cut by the lake shoreline leaving many of lake terraces. And the young fans cut across the lake terraces and the old fans. By contrasting to the "Paleo-Qiangtang Huge Lake" since late Quaternary, these old alluvial fans could be late Pleistocene with age ranging from 40ka to 50ka. And the young fans could be Holocene. The sag ponds along the BZF are distributed in the late Pleistocene alluvial fans. Also, the BZF displaced the late Pleistocene fans without traces within Holocene fans, suggesting that the BZF is a late Pleistocene active fault. The fault scarps are gentler with the slope angle of around 10° and the vertical offset is about 2m by field measurement. Reconstruction of the offset of channels suggested that the accumulated dextral offset could be about 44m on the late Pleistocene alluvial fans. Therefore, we infer that the dextral slip-rate could be around 1mm/a showing a low-rate deformation characteristic. The angle between the strike of BZF and principal compressive stress axis(σ1)is around 30°, which is significantly different to the other faults within the conjugate strike-slip fault zones that is 60°~75°. Now, the deformation mechanisms on these conjugate faults are mainly proposed in the studies of obtuse angle between the faults and σ1, which is likely not applicable for the BZF. We infer that the BZF could be the northward prolongation of the north-trending rifts based on the geometry. This difference suggests that the conjugate strike-slip faults may be formed by two different groups:one is obtuse angle, which is related to block extrusion or shear zones in Lhasa and Qiangtang terranes possibly; the other is acute angle, which may represent the characteristics of new-born fractures. And more studies are needed on their deformation mechanisms. 相似文献
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ANALYSIS OF EVOLUTION OF THE RIYUESHAN FAULT SINCE LATE PLEISTOCENE USING STRUCTURAL GEOMORPHOLOGY 下载免费PDF全文
下载免费PDF全文 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. 相似文献