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1.
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
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佛洞庙-红崖子断裂位于祁连山北缘断裂带中段,是1条活动逆断裂。在佛洞庙-红崖子断裂东、中、西各段落开挖整理了5个探槽。通过探槽揭示的各地层单元的沉积特征、各单元之间的层序关系以及断层对不同地层的切割关系,共辨认出了4次古地震事件。根据探槽中各地层单元的14C样品和光释光样品测年结果,对4次古地震事件给出了年龄制约:最早事件E4发生在距今约10.6ka,事件E3发生在距今约7.1ka,事件E2发生在距今约3.4ka,事件E1为1609年红崖堡地震。这4次地震事件的间隔分别约3.5ka、3.7ka和3.0ka,平均复发间隔约3.4ka,具有准周期重复特征。 相似文献
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野外调查表明 ,口泉断裂断错了断面附近的 3级地貌面 ,包括大同盆地西侧全新世形成的洪积扇后缘及位于洪积扇冲沟内的Ⅰ ,Ⅱ级阶地。其中冲沟内Ⅱ级阶地为剥蚀阶地 ,Ⅰ级阶地为堆积阶地 ,Ⅰ级阶地面的地层时代距今 2 52ka。在该断裂的悟道及上黄庄 2个地点开挖的大探槽表明 ,在距今 1 2 3万年以来该断裂曾发生 4次古地震事件 ,其中 3次分别发生在接近距今 2 52 ,5 6 8,13 73ka。另一次古地震事件发生在距今 6 76～ 10 82ka。这些数据有可能反映了口泉断裂具备准周期的强震活动。这 4次古地震事件的平均间隔约为 3 74ka ,最新一次古地震与上一次事件的时间间隔约为 3 16ka。 2个大探槽各次事件的平均最小同震垂直位移为 1 8m。这些资料对重新评价口泉断裂未来的地震潜势具有重要意义 相似文献
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夏垫断裂是北京平原区内1条极为重要的隐伏活动断裂,同时也是1679年三河—平谷MS8.0地震的发震断层。为获取该断裂完整的古地震序列,主要开展了2方面工作:(1)以大胡庄探槽原始资料为基础,重新对探槽进行了解译,共识别出3个埋藏古土壤,6个崩积楔和1次砂土液化现象;(2)结合该断裂其它部位探槽揭示的古地震事件,通过对比各探槽标志性地层,建立不同探槽中古地震事件在同一时间轴上的联系,得到夏垫断裂完整的古地震序列。结果表明:距今31 ka以来,夏垫断裂共发生过11次古地震事件,古地震平均复发间隔约为2.8ka,但距今25~15 ka存在1个古地震丛集期,丛集期内共发生5次强震,平均复发间隔约为2.0 ka,反映出夏垫断裂活动性存在阶段性的差异。 相似文献
5.
乌鲁木齐西山断裂组与地表破裂型逆断层古地震识别标志 总被引：3，自引：5，他引：3
乌鲁木齐西山断裂层组展布于北天山山前断展褶皱系与博格达推覆构造系的转换部位,为盆地向S推覆的构造,由4～5条长度十几公里至近30km的断层组成,其滑脱面埋深约11km。通过地质地貌调查、探槽开挖,结合深部构造特征分析,西山断裂组晚更新世中晚期有明显的活动。断层F1—F3最年轻的2次事件基本都被限制在距今(22.7±5.2)ka和40ka左右。而F4和西山断裂最年轻的事件被距今31.0ka和38.0ka的地层覆盖。这显示西山断裂组晚第四纪活动有分组和组合破裂的特征。断层F4和西山南缘断裂为一组,F1—F3为另一组。坎前堆积地层、断层与堆积地层的切错关系和不同间断面或标志地层在断层两侧的累积位差的突变,是识别地表破裂型逆断层古地震事件的重要标志。降低逆断层古地震识别的不确定性,关键在于识别事件的标志需要综合分析各种影响因素,有多证据的支持 相似文献
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《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
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前人在山西交城断裂带上开挖过多个探槽,揭露出全新世3次古地震事件,但其研究结果尚不能确定该断裂带全新世活动段的北部边界.近期在该断裂带北端和中段又开挖了3个大型探槽,其中在阳曲县泥屯盆地西界开挖的龙王沟探槽,是一个由多个探槽组合成的大探槽,该探槽揭示的地层断错信息,将交城断裂带全新世活动的范围向北延伸了20km.另外2个大型探槽分别为交城断裂带中段瓦窑沟东侧台地前缘的瓦窑探槽与市儿口沟西侧T1阶地前缘的新民探槽.这3个大探槽均揭示出全新世中期(14C测年值为距今5 ～ 6ka)的垆土和淤泥层,以及多组平行分布的断面,所揭示的全新世3次古地震事件具有断错事件活动的同步性,可与前人探槽揭示的全新世断层活动事件相对比.3次断错活动时间分别距今3.06 ～3.53ka、5.32ka左右或6.14ka左右、8.36ka左右;3次事件的时间间隔分别为2.02 ～ 2.84ka和2.22 ～ 3.04ka.这些断错事件的同震垂直位移为1.5～4.7m,显示了7级以上地表破裂型的强震活动.最后讨论了探槽中14C测年样品的影响因素. 相似文献
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柯坪推覆构造的根部断裂记录到的地震活动相对较弱,以至于多数学者认为该断裂晚第四纪以来活动性不强。笔者根据遥感影像解译和野外调查得到迈丹断裂的几何展布,确认F3阿合奇段为最新地表破裂带,并通过一系列河流阶地的左旋位移测量确定其晚更新世以来有过走滑活动。结合地貌测量和探槽开挖得到断层垂直错距,探槽揭示的古地震事件发生在距今(1.76±0.22)ka之后,根据现场考察获得的活动构造定量数据,依据不同震级与地表破裂关系式推算出该次古地震震级为7.5级。研究成果可能对区域活动断裂的研究以及区域活动构造图像的完整性提供基础资料,同时最新地表破裂证据的发现可能有助于更新认识该断裂的危险性。 相似文献
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10.
蔚广盆地南缘断裂带唐山口段山前断层活动性研究 总被引：1，自引：0，他引：1
蔚广盆地是山西地堑系北端京西北盆岭构造区内的一个半地堑盆地，蔚广盆地南缘断裂带为控制该盆地形成的边界断裂。该断裂带位于唐山口段的山前断裂在冲洪积扇体上形成了线性特征显著的断层陡坎。横跨断层陡坎开挖的探槽表明该条山前断裂属于全新世活动断裂，探槽揭示了2条活动断层以及相应的3次古地震事件。在距今约9ka时其中一条断层首次活动，之后在距今约7.3ka时该条断层再次活动并引发了另一条断层的形成与同步活动。最后它们又发生了第三次活动，而最新一次活动的时间由于相应地表沉积的缺失而无法获得。这3次古地震事件的累积垂直位错约为8.1m。估算出整条山前断裂的平均复发周期约为1.7ka、平均滑动速率约为1.6mm/a。此外还依据经验公式估算出了各次古地震的参考震级。 相似文献
11.
The Fodongmiao-Hongyazi Fault is a Holocene active thrust fault, belonging to the middle segment of northern Qilianshan overthrust fault zone, located in the northeastern edge of the Tibet plateau. The Hongyapu M7(1/4) earthquake in 1609 AD occurred on it. A few paleo-seismology studies were carried out on this fault zone. It was considered that four paleoearthquakes occurred on the Fodongmiao-Hongyazi Fault between(6.3±0.6) ka BP and(7.4±0.4) ka BP, in(4.3±0.3) ka BP, in(2.1±0.1) ka BP and in 1609 AD. The occurrences of the earthquakes suggested the quasi-periodic characteristic with a quasi-periodic recurrence interval between 1 600~2 500a(Institute of Geology, State Seismological Bureau, Lanzhou Institute of Seismology, State Seismological Bureau. 1993; Liu et al., 2014). There was no direct evidence for the Hongyapu M7(1/4) earthquake in 1609 AD from trench research in the previous studies. Great uncertainty exists because of the small number of the chronology data, as a few TL and OSL measurement data and several14 C data, and it was insufficient to deduce the exact recurrence interval for the paleoearthquakes.
Five trenches were excavated and cleared up respectively in the eastern segment, middle segment and western segment along the Fodongmiao-Hongyazi Fault. After detail study on the trench profiles, the sedimentary characteristics, sequence relationship of the stratigraphical units, and fault-cuts in different stratigraphical units were revealed in these five trenches. Four paleoearthquakes in Holocene were distinguished from the five trenches, and geology evidences of the Hongyapu M7(1/4) earthquake in 1609 AD were also found.
More accurate constraint of the occurring time of the paleo-earthquakes since Holocene on the Fodongmiao-Hongyazi Fault is provided by the progressive constraining method(Mao and Zhang, 1995), according to amounts of 14 C measurement data and OLS measurement data of the chronology samples from different stratigraphical units in the trenches. The first paleoevent, E4 occurred 10.6ka BP. The next event, E3 occurred about 7.1ka BP. The E2 occurred about 3.4ka BP. The last event, E1 is the Hongyapu M7(1/4) earthquake in 1609 AD.
Abounds of proofs for the occurrences of the events of E1, E2 and E3 were found in the trench Tc1, trench Tc2, trench Tc4 and trench Tc3, located in the eastern, middle and western segments of the Fodongmiao-Hongyazi Fault accordingly. It's considered that the events E1, E2 and E3 may cause whole segment rupturing according to the proofs for these three events found together in individual trenches. The event E4 was only found in the trench Tc5 profile in the west of the Xiaoquan village in the eastern segment of the Fodongmiao-Hongyazi Fault. The earthquake rupture characteristics of this event can't be revealed before more detailed subsequent research.
The time intervals among the four paleoearthquakes are ca 3.5ka, ca 3.7ka, and ca 3.0ka. The four events are characterized by ca 3.4ka quasi-periodic recurrence interval. 相似文献
12.
The Dengdengshan and Chijiaciwo faults situate in the northeast flank of Kuantanshan uplift at the eastern terminal of Altyn Tagh fault zone, striking northwest as a whole and extending 19 kilometers and 6.5 kilometers for the Dengdengshan and Chijiaciwo Fault, respectively. Based on satellite image interpretation, trenching, faulted geomorphology surveying and samples dating etc., we researched the new active characteristics of the faults. Three-levels of geomorphic surfaces, i.e. the erosion rock platform, terrace I and terrace Ⅱ, could be found in the northeast side of Kuantanshan Mountain. The Dengdengshan Fault dislocated all geomorphic surfaces except terrace I, and the general height of scarp is about 1.5 meters, with the maximum reaching 2.6 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 2.7 meters, the average vertical dislocation of each event changed from 0.5 to 1.2 meters. By collecting age samples and dating, the event Ⅰ occurred about 5ka BP, event Ⅱ occurred about 20ka BP, and event Ⅲ occurred about 35ka BP. The recurrence interval is about 15ka BP; and the vertical slip rate since the late Pleistocene is about 0.04mm/a.
The Chijiaciwo Fault, however, dislocated all three geomorphic surfaces, and the general scarp height is about 2.0 meters with the maximum up to 4.0 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 3.25 meters, the average vertical dislocation of each event changed from 0.75 to 1.5 meters, and the vertical slip rate since the late Pleistocene is about 0.06mm/a. Although the age constraint of paleoearthquakes on Chijiaciwo Fault is not as good as that of Dengdengshan Fault, the latest event on Chijiaciwo Fault is later than Dengdengshan Fault's. Furthermore, we infer that the recurrence interval of Chijiaciwo Fault is 15ka BP, which is close to that of Dengdengshan Fault.
The latest event on Chijiaciwo Fault is later than the Dengdengshan Fault's, and the vertical displacement and the slip rate of a single event in late Quaternary are both larger than that of Dengdengshan Fault. Additionally, a 5-kilometer-long discontinuity segment exists between these two faults and is covered by Quaternary alluvial sand gravel. All these indicate that the activity of the Chijiaciwo Fault and Dengdengshan Fault has obvious segmentation feature.
The size of Chijiaciwo Fault and Dengdengshan Fault are small, and the vertical slip rate of 0.04~0.06mm/a is far smaller than that of Qilianshan Fault and the NW-striking faults in Jiuxi Basin. All these indeicate that the tectonic deformation of this region is mainly concentrated on Hexi Corrider and the interior of Tibet Plateau, while the activties of Chijiaciwo and Dengdengshan faults are characterized by slow slip rate, long recurrence interval(more than 10ka)and slow tectonic deformation. 相似文献
13.
ACTIVITY FEATURES OF FAULTS AT THE EAST OF ZHANGSHAN ON THE MIDDLE SEGMENT OF TANLU FAULT ZONE 
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下载免费PDF全文 Given the scarcity of research on the activity of Xinyi-Sihong segment of the Tanlu Fault zone, this paper focuses on the Zhangshan segment where there are quite evident geomorphic features to complement the shortage of the research on the northern part of Xinyi-Sihong segment. This study enriches evidences for the late Quaternary activity and paleoseismological events on the Xinyi-Sihong segment. The Zhangshan segment is located at Xiaodian Town to Jintou Village of Suqian City, stretching towards NE for 7 kilometers with a dip angle of 60~80. Research of tectonic geomorphology shows that gullies in northern part of Zhangshan segment were evidently displaced, while in the southern, two NE-trending right-stepped fault scarps are developed, with an average height of 3 meters, which generally suggests that the fault was dominated by thrust and dextral motion. Two trenches were excavated in the southern part of Zhangshan segment, numbered Mayao trench 1 and Mayao trench 2. Both trenches reveal that:(1)within this segment, Tanlu Fault shows periodic fault activity, that is, normal faulting during Pliocene epoch while thrust faulting in Quaternary period; (2)an event occurred between 15.12ka BP to 11.82 BP; (3)the latest event possibly took place around 3 500 a BP. Based on integrated results of previous studies, we identify the dates of paleoseismic events on the Xinyi-Sihong segment as follows:more than 960 thousands years ago, early to middle period of late Pleistocene, (15.12~11.82)ka BP, (11.76±0.05)ka~(10.53±0.05)ka BP, (10.15±0.05)ka~(8.16±0.05)ka BP and 4 960~3 510a BP. 相似文献
14.
The Bolokenu-Aqikekuduk fault zone(B-A Fault)is a 1 000km long right-lateral strike-slip active fault in the Tianshan Mountains. Its late Quaternary activity characteristics are helpful to understand the role of active strike-slip faults in regional compressional strain distribution and orogenic processes in the continental compression environment, as well as seismic hazard assessment. In this paper, research on the paleoearthquakes is carried out by remote sensing image interpretation, field investigation, trench excavation and Quaternary dating in the Jinghe section of B-A Fault. In this paper, two trenches were excavated on in the pluvial fans of Fan2b in the bulge and Fan3a in the fault scarp. The markers such as different strata, cracks and colluvial wedges in the trenches are identified and the age of sedimentation is determined by means of OSL dating for different strata. Four most recent paleoearthquakes on the B-A Fault are revealed in trench TC1 and three most recent paleoearthquakes are revealed in trench TC2. Only the latest event was constrained by the OSL age among the three events revealed in the trench TC2. Therefore, when establishing the recurrence of the paleoearthquakes, we mainly rely on the paleoearthquake events in trench TC1, which are labeled E1-E4 from oldest to youngest, and their dates are constrained to the following time ranges: E1(19.4±2.5)~(19.0±2.5)ka BP, E2(18.6±1.4)~(17.3±1.4)ka BP, E3(12.2±1.2)~(6.6±0.8)ka BP, and E4 6.9~6.2ka BP, respectively. The earthquake recurrence intervals are(1.2±0.5)ka, (8.7±3.0)ka and(2.8±3)ka, respectively. According to the sedimentation rate of the stratum, it can be judged that there is a sedimentary discontinuity between the paleoearthquakes E2 and E3, and the paleoearthquake events between E2 and E3 may not be recorded by the stratum. Ignoring the sedimentary discontinuous strata and the earthquakes occurring during the sedimentary discontinuity, the earthquake recurrence interval of the Jinghe section of B-A Fault is ~1~3ka. This is consistent with the earthquake recurrence interval(~2ka)calculated from the slip rate and the minimum displacement. The elapsed time of the latest paleoearthquake recorded in the trench is ~6.9~6.2ka BP. The magnitude of the latest event defined by the single event displacement on the fault is ~MW7.4, and a longer earthquake elapsed time indicates the higher seismic risk of the B-A Fault. 相似文献
15.
Geomorphic study on Wjiahe segment of Serteng piedmont fault,Inner Mongolia is made.Throuth analysis of the available data in combination with the results of predecessors‘studies it can be obtained that average vertical displacement rate is 0.48-0.75mm/a along the Wujiahe segment since the late Pleistocene(14.450-22.340ka BP)and 0.56-0.88mm/s since the early-middle Holocene(5.570-8.830ka BP).Analyzing paleoseismic phenomena revealed in the excavated 5trenches in combination with the results of predecessors‘studies of paleoearthquakes on the fault,we determine five paleoseismic events on the Wujiahe segment of Serteng piedmont fault since 27.0ka BP and the recurrence interval to be about 4.300-4.400ka,A cluster of paleoearthquakes occurred probably during 8.000-9.000ka BP and two paleoeismic events in 10.000-20.000ka BP may be missed.A comparison between height of fault scarps and sum of displacement caused by paleoseismic events revealed in trenches,and recurrence interval of paleoseismic events obtained from average displacement rate along the fault and the disloca-tion by one event suggest that three paleoseismic events are absent in Alagaitu trench.Two paleoseismic events may be absent on the whole active fault segment. 相似文献
16.
山西峨嵋台地北缘断裂是汾渭断陷带内临汾-侯马盆地与峨嵋台地隆起之间的边界断裂,对临汾-侯马盆地内的侯马次级盆地具有控制作用。该断裂自西向东分为西、中、东3段,西段为早中更新世活动,中段为全新世活动,东段为晚更新世活动。在断裂中段的任庄村和金沙村附近开挖了两个探槽,通过对探槽所揭露的古地震事件的年代学分析,结合前人研究结果,认为峨嵋台地北缘断裂全新世发生过A1及A2两次古地震事件,年代分别为466a BC、约4.6ka BP。事件A1即史料记载的466a BC晋空桐地震,震级可能达71/2级。 相似文献
17.
Along the northern piedmont of Mt. Lishan, the characteristics and locations of the active normal Lishan fault in west of Huaqing Pool provide important evidences for determining the seismotectonic environment, seismic stability evaluation of engineering in the eastern Weihe Basin. After reviewing the results from high-density resistivity method, seismic profile data, geological drillhole section and trenching in west of the Huaqing Pool, it is found that the strike of western normal Lishan Fault changes from EW direction at the eastern part to the direction of N60°W, and the fault consists of two branches, dipping NE with a high dip angle of~75°. The artificial shallow seismic profile data reveals that the attitude of strata near Lishan Fault mainly dips to south, which is presumed to be related to the southward tilt movement of Mt. Lishan since the Cenozoic. The section of geological drillhole reveals that since the late middle Pleistocene, the displacement of the paleo-soil layer S2 is about 10m. And the maximum displacement of western Lishan Fault recorded in the paleo-soil layer S1 reaches 7.8m since the late Pleistocene.
In addition, evidences from trench profile show that the western Lishan Fault was active at least 3 times since Malan loess deposition with 14 C dating age(32 170±530)Cal a BP. The multiple activities of the Lishan Fault result in a total displacement about 3.0m in the Malan loess layer L1. The latest activity of the western Lishan Fault produced a displacement of about 0.9m in the early Holocene loess layer L0((8 630±20)Cal a BP)and caused obvious tensile cracks in the Holocene dark leoss layer S0((4 390±20)Cal a BP). Briefly, we have obtained a vertical movement rate of about 0.11~0.19mm/a since the Holocene((8 630±20)Cal a BP)in the western extension of the Lishan Fault, the recurrence interval of earthquakes on the fault is about(10.7±0.5)ka, and the co-seismic surface rupture in a single event is inferred to be about 0.9m. 相似文献
18.
DONG Shao-peng ZHANG Pei-zhen ZHENG Wen-jun YU Zhong-yuan LEI Qi-yun YANG Hui-li LIU Jin-feng GONG Hui-ling 《地震地质》2018,40(6):1216-1239
The Langshan range-front fault (LRF)is a Holocene active normal fault that bounds the Langshan Mountain and Hetao Basin at the northwest corner of the Ordos Plateau. Paleoseismic trenching research at three sites, Dongshen Village trench (TC1), Qingshan trench (TC2)and Wulanhashao trench (TC3)from north to south was performed in this study to reveal the seismic hazard risk in Hetao Basin. The paleoevents ED1, ED2, ED3 from TC1 can be constrained to have occurred (6±1.3)ka, (9.6±2)ka and (19.7±4.2)ka respectively, while the paleoevent EQ1 from TC2 occurred about (6.7±0.1)ka and the paleoevents EW1, EW2, EW3 at TC3 took place about (2.3±0.4)ka, (6±1)ka and before 7ka respectively. In combination with paleoseismic results of previous researchers, the Holocene earthquake sequence of the LRF could be established as 2.3~2.43ka BP (E1), 4.41~3.06ka BP (E2), 6.71~6.8ka BP (E3), 7.6~9.81ka BP (E4), and (19.7±4.2)ka BP (E5). Although the possibility of missing events cannot totally be ruled out, based on the analysis on faulted geomorphology at Wulanhashao site, we argue the paleoearthquake history of the LRF during Holocene may be complete with an average recurrent interval about 2500 yrs. The apparent displacements associated with events E1, E3 and E4 are significantly larger than that of event, E2, that suggests that they might be great events with magnitudes 7.5 to even over 8 that ruptured the entire LRF, while the event E2 may be a smaller event that only ruptured a segment of the fault. The magnitude of event E2 might be about M7. This poses a significant seismic hazard to the area of the Linhe depression in the western Hetao graben region. With the further limitation of previous radiocarbon dating result near our trench site at Wulanhashao, the slip rate at Wulanhashao should be not smaller than, but close to 0.66mm/a since 15ka BP. And the slip rate at Qingshan site is supposed to be about 1.4~1.6mm/a since 6.8ka BP. Both our combined most recent paleoseismic cognition and current tectonic geomorphologic research results supports to reveal that the Langshan range-front fault now is an unsegmented fault, preferring to rupture the whole fault in a surface-rupture event. Considering the most recent event E1 and fault slip rate obtained above, the accumulated strain on the LRF could be estimated as about 1.52~3.94m. Given the ~2500a recurrent interval, we argue that the elapsed time since last major quake, E1, is approaching or even over the recurrence, and the seismic risk for another major quake is imminent, at least cannot be ignored. 相似文献
19.
The relationship between the latest activity of active fault and seismic events is of the utmost importance. The Tan-lu fault zone in eastern China is a major fault zone, of which the active characteristics of the segments in Jiangsu, Shandong and Anhui has been the focus of research. This study takes the Dahongshan segment of the Tanlu Fault in Sihong County as the main research area. We carried out a detailed geological survey and excavated two trenches across the steep slope on the southwest side of the Dahongshan. Each trench shows fault clearly. Combining the comparative analysis of previous work, we identified and cataloged the late Quaternary deformation events and prehistoric earthquake relics, and analyzed the activity stages and behavior of this segment.
Fault gonge observed in the trench profiles shows that multiple earthquake events occurred in the fault. The faulting dislocated the Neogene sandstone, black gravel layer and gray clay layer. Brown clay layer is not broken. According to the relations of dislocated stratums, corresponding 14C and OSL samples were collected and dated. The result indicates that the Dahongshan segment of the Tanlu Fault has experienced strong earthquakes since the late Quaternary. Thrust fault, normal fault and strike-slip fault are found in the trenches. The microscopic analysis of slices from fault shows that there are many stick-creep events taking place in the area during the late Quaternary. Comprehensive analysis shows that there have been many paleoearthquakes in this region since the late Quaternary, the recent active time is the late Pleistocene, and the most recent earthquake event occurred in(12~2.5ka BP).
The neotectonic activity is relatively weak in the Anhui segment(south of the Huaihe River)of Tanlu fault zone. There are difficulties in the study of late Quaternary activity. For example, uneven distribution of the Quaternary, complex geological structure, larger man-made transformation of surface and so on. The progressive research may be able to promote the study on the activity of the Anhui segment of Tanlu fault zone. 相似文献