河北省阳原六棱山北麓断裂古地震年代学的初步研究

六棱山北麓断裂位于阳原盆地南缘，是一条总体走向北东东，倾向北北西的倾滑正断裂。它的断错地貌在河北阳原独山堡发育最好且保存完整在，在狡山堡六棱山北麓断层陡坎前缘开挖了２个探槽，共揭示了２次古地震事件；采集了多个测年样品，经红外释光（ＩＲＳＬ）测年技术测定，初步获得了２次古地震事件发生的可能时代。     

Paleoseismic activity on Wujiahe segment of Serteng piedmont fault,inner Mongolia

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.     

秦岭北麓晚第四纪断层陡坎的初步研究

根据航片解译和野外调查,发现在秦岭北麓第四纪松散沉积物中发育有断层陡坎,本文依据对这些陡坎的地质地貌分析、地形剖面测制、探槽揭露及测年数据,讨论了断层陡坎的空间分布和形态学特征、生成时代和断距,评估了秦岭北麓断裂在晚第四纪的活动强度。由断层陡坎高度经过校核获得断距变化范围在1.1至7.9米之间,由此求得秦岭北麓断裂中段全新世中晚期以来平均滑动速率接近1mm/a,西段在眉县一带为0.5mm/a左右。晚更新世以来,发生过3—4次古地震事件     

中国大陆古地震研究的关键技术与案例解析(3)——正断层破裂特征、环境影响与古地震识别

正断层在中国大陆地区广泛存在。由于地表破裂个性的存在和堆积环境的不同,要揭露真实、完整的古地震活动历史,一些问题需要认真关注和讨论。从正断层大地震地表破裂特征、一般识别标志,结合中国正断层古地震研究的案例和地质地貌、气候环境可能造成的影响,提出在中国开展正断层古地震研究,需注意的技术要点：1）因地制宜地选择探槽开挖位置。宜选择断层错动面简单、单次位移量不太大、外力的侵蚀与堆积作用相对平衡、堆积物粒度中细、能取到测年样品的地段开挖探槽;应尽量避免在断错地层以黄土、次生黄土或块状亚砂土等为主的地区,若避不开这类地点,可考虑小冲沟附近,有少量上游不同成分堆积物的地点开挖探槽。2）精细的探槽记录与分析。对于黄土等块状堆积,要特别注意颜色、粒度、排列方向的细微变化可能暗示着接触界线;识别崩积楔等的要素是崩塌相中杂乱结构和团块状物质,冲刷相上部发育的土壤层;对于坎前堆积物主要为黄土或次生黄土等不易分辨的物质时,细致辨别堆积单元的颜色、粒度、非黄土类物质和钙富集程度等。3）综合的识别技术与检验方法。“逐次限定”方法、“位移量限定法”和 “多探槽校验法”,断错事件的重建等,有助于判断所确定的古地震是否真实和完整。     

山西六棱山北麓晚第四纪不规则断裂作用的地貌学研究

利用航片判读和野外核查相结合的途径确定了六棱山北麓晚第四纪时期的基本地貌单元及其形成时代，研究了六棱山北麓断裂的地貌学和构造学分段性特征，通过对断错地貌面的地形剖面的高精度实测，获得了表征六棱山北麓断裂作用时空不规则性的定量资料──晚第四纪断层滑动速率随时间的涨落特性，指出距今１．５６～０．７６万ａ时段是六棱山北麓断裂作用的强烈活跃期     

Late Quaternary Activity and Paleoearthquakes along the Nanyukou Segment of the Northern Piedmont Fault of Wutai Mountain

The northern piedmont fault of Wutai Mountain is located at the north of the Shanxi Graben system,which is the dominating fault of the south boundary of the Fanshi-Daixian depression. This paper discusses the fault activity and paleoearthquakes around the Nanyukou segment of the northern piedmont fault of Wutai Mountain during the late Quaternary through field investigation along the fault,measuring geomorphic deformation and excavating trenches at some important sites. From Nanyukou to the southwest of Shanhui,we find obviously dislocated alluvial fans,with strong neotectonic movement at these sites. Since nearly 20ka,the vertical average slip rate is 1. 55mm /a to 2. 0mm /a. However,since nearly 6ka,it has reached as high as 2. 3mm /a,which is twice that on other segments. 2 trenches were excavated around Nanyukou with 6 events discovered. The referenced ages of the events are before 7600a,6700a ～ 7600a,5321a ～ 5575a,4400a ～ 5400a,4200a ～ 4400a and after 1600a B. P. with approximate recurrence interval 1400a. The latest event is likely to be the earthquake occurring at 512 A. D. ,so it is necessary to do further work to verify this in the future.     

Paleoseismicity and Segmentation Along the Active Fault at the Northern Boundary of Huailai-Zhuolu Basin,Hebei Province

The northern boundary fault of Huailai-Zhuolu basin,Hebei Province,has a total length of 58 km and a general strike of NE.The geometry and feature of activity of the 5 segments of the fault greatly differ from each other.17 paleoseismic events have been recognized within 11 trenches excavated along the different segments of the fault.It is found that each segment is characterized by its distinct recurrence of paleoearthquakes.The recurrence intervals of strong earthquakes for each segment are 3500-7000 a for the shortest and 17,000-20,500 a for the longest.However,the recurrence interval of strong earthquakes for whole fault ranges between 750-8500 a.The boundary of the segments can be recognized as the junction,gap,bending,jog and salient of the fault.The length of the segment ranges between 7.5-14 km.     

山西交城断裂北端及中段3个大型探槽全新世断错现象分析

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.     

新疆阜康—吉木萨尔断层晚第四纪活动与变形特征的新认识

阜康—吉木萨尔断层是博格达山体与山前冲洪积平原的分界断层，全新世以来仍在活动，山前的冲洪积平原和河流低级阶地均发生了不同程度的拱曲变形，断层剖面揭示了该断层晚更新世末期有3次古地震事件。断层近地表后倾角变缓，地表的陡坎地形主要是由地层的拱曲变形形成的，反映了断层近地表位错的消减和分配规律。     

山西高原六棱山北麓断裂晚第四纪运动学特征初步研究

六棱山北麓断裂是山西地堑系北端张性构造区中的一条控制性断裂，总体走向北东东、倾向北北西，是一条至今仍在活动的倾滑正断裂，控制阳原盆地的形成和发展。在１９９３年和１９９４年的中日合作研究中，我们对断裂分段特征进行了研究，并用Ａｕｔｏ－ｌｅｖｅｌ仪器对这一条断裂晚第四纪不同时期的断错地貌面的位错量进行了测量，对这些地貌面的年龄进行了测定，得到该断裂带晚更新世晚期至全新世时期的平均垂直滑动速率为０．４３～０．７５ｍｍ／ａ。关键词     

焉耆盆地北缘和静逆断裂-褶皱带古地震破裂方式和时间序列

古地震研究是构造地质基础研究工作之一,获得较为精细的古地震结果有利于提高对断层构造变形的样式、强度以及时间的认识。焉耆盆地是南天山东段的山间盆地,现今的构造应力场特征以挤压兼有走滑为主。盆地南北缘断裂均为全新世活动断裂,南缘开都河断裂以走滑运动为主。盆地北缘断裂向盆内扩展的新生和静逆断裂-褶皱带以逆冲运动为主,且具备发生7级以上大地震的能力。因此,对于焉耆盆地北缘和静逆断裂-褶皱带的古地震破裂方式和发生时间的研究具有重要意义。调查发现,其中的哈尔莫敦背斜南翼主逆断裂以30°左右向盆内逆冲,在河漫滩和T1阶地上形成了3排断层陡坎。在3条断层陡坎上开挖的5个探槽中,通过标志地层建立的时间序列可以确定6次古地震事件的先后关系。利用14C和光释光(OSL)测年手段获得了探槽中相关地层和坎前堆积物的沉积时代,利用逐次限定法得到了各次古地震事件的发生时间和全新世以来2ka左右的古地震复发间隔。结果显示F1断层在所有的古地震事件中都发生了破裂,F2断层只在事件E时产生了破裂,F3断层只在事件D和事件E中发生过破裂。从古地震事件上分析,事件D是一次3条断层同时破裂的事件,事件E是一次F1和F32条断层同时破裂的事件,其他事件都只在F1断层上破裂。和静逆断裂的古地震破裂同时存在必然性和不确定性。     

则木河断裂带大箐梁子附近古地震组合探槽研究

古地震事件定年具不确定性,为了增加地震事件定年的可信度,文中通过断层活动方式、沉积环境和地震微地貌的综合分析来研究则木河断裂带上的古地震事件。在大箐梁子附近开挖组合探槽,揭露了3次古地震事件,分别距今约160a、3100a和5500～8900a,复发间隔为3000a左右;讨论了与走滑断层型地震相关的沉积过程,揭示了走滑断层在山坡部位形成鼓包和反向陡坎情况下的沉积模式     

则木河断裂带北段地震地貌及古地震研究

地震形成的构造微地貌是地震破裂在地表的直接证据,因此微地貌分析是古地震研究中的一种有效的方法。本文通过对则木河断裂北段大箐梁子一带发现的断层陡坎、断错冲沟、“搓衣板”地貌及坡中谷等地震地貌的研究,发现该断裂自晚更新世晚期以来至少发生过四次强震,其中历史上有记载的两次地震在地貌上也有所反映,说明在则木河断裂带上,强震亦具有在原地重复发生的特点。全新世以来,7级以上强震在原地复发的最小间隔约为1000年,其平均间隔约为1800年     

ACTIVITY FEATURES OF FAULTS AT THE EAST OF ZHANGSHAN ON THE MIDDLE SEGMENT OF TANLU FAULT ZONE

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.     

大凉山断裂带北段石棉断裂的古地震

大凉山断裂带是大型走滑断裂鲜水河-小江断裂系的重要组成部分,其活动性是认识和探讨青藏高原东南缘现今地震活动和构造变形机制的重要基础资料.相较于中段和南段,关于大凉山断裂带北段活动性的相关研究成果,尤其是古地震资料非常缺乏.文中基于野外地质地貌调查,在石棉断裂联合村处开挖了一组(2个)探槽,揭露出断裂全新世活动的直接证据...     

正倾滑活动断裂垂直位移定量研究中相关问题的讨论

当探槽开挖长度未跨过断层变形带时，得到的断层垂直位移将偏离断层活动的真实情况，在缺少依据帮助确定断层陡坎原始下坡角的具体位置时，通过断层陡坎高度获得的断层垂直位移也将与实际情况有较大的偏离，文中对此进行了讨论。并讨论了应用断层两侧近水平地层累积变位量的分解确定古地震事件期次的方法，以及探槽剖面中断层两侧同层地层厚度差异是断层活动事件的反映等问题。引用了内蒙古大青山山前断裂和狼山山前断裂、北京平原夏垫断裂和南口－孙河断裂及日本丹那断层探槽开挖的实例。     

四川大凉山断裂带古地震研究初步结果

沿四川大凉山断裂带的 4条次级断裂开挖了 4个探槽 ,共揭露出 9次古地震事件。根据探槽中年龄样品的测试结果 ,分析了各次事件的距今年龄及其重复间隔。其中 ,有 3个探槽共揭露出4次全新世以来的古地震事件。 9次古地震的垂直位移量在 0 5～ 1 5m之间 ,与鲜水河 -小江断裂带历史地震所产生的垂直位移量进行对比 ,估计它们的震级都在 7级以上     

Rare destructive earthquakes in Europe: The 1904 Bulgaria event case

Seismic hazard is difficult to assess in regions of low strain rates. A major limitation often relates to the absence of large instrumentally recorded events precluding any comparison between seismological data and paleoseismic or morphotectonic informations. We take advantage of the 1904 M_s∼7.1 earthquake that struck the southern edge of stable Eurasia and investigate if morphotectonic and paleoseismic observations can provide a reliable estimate of the seismic potential of slow-slipping faults. We have conducted a paleoseismic study of the Krupnik normal fault thought to be responsible for the event. A section of the fault bearing remnants of a 2 m-high scarp has been selected at the base of triangular facets. The trenching site locates where the scarp cuts across colluviums washed from the bedrock facetted slopes. We excavated two neighbouring trenches, one across a well-preserved portion of the scarp, and one across a portion degraded by a landslide. The excavations reveal a set of coarse colluvial units faulted against bedrock and affected by secondary fissures. Faulting appears to have resulted from a single event with normal throw greater than 1.3 m that occurred before the emplacement of the landslide. Accelerator Mass Spectrometry (AMS) radiocarbon dates of charcoal samples are consistent with the interpretation that the Krupnik Fault slipped recently, most probably in 1904, after a long lasting (> 10 ka) period of quiescence. The morphotectonic and paleoseismic observations yield seismic moment estimates compatible with the instrumental magnitude of the event and indicate that destructive and infrequent earthquakes typify the regional seismic behaviour.     

PALEOEARTHQUAKES ALONG PUXIONG FAULT OF DALIANGSHAN FAULT ZONE DURING LATE QUATERNARY

Daliangshan fault zone (DFZ) constitutes an indispensable part of Xianshuihe-Xiaojiang fault system which is one of the main large continental strong earthquake faults in China.Puxiong Fault,the east branch of middle segment of DFZ,is the longest secondary fault.Its paleoseismic activity plays an important role in evaluating regional seismic activity level and building countermeasures of preventing and reducing the earthquake damage.The active fault mapping as well as the study of paleoseismological trench in recent years illustrates that Puxiong Fault is a slightly west-dipping high-angle left-lateral strike-slip fault with strong activity since late Pleistocene.Two trenches excavated across this fault reveal 2 and 3 paleoearthquakes that ruptured the fault at 8206 BC-1172 AD,1084-1549 AD,and 17434-7557 BC,1577-959 BC and 927-1360 AD,respectively.The OxCal model combining the results from both trenches and the another one in previous study across the fault with the historical earthquake record yields the elapsed time of~0.7ka of the latest paleoearthquake event,and the interval time is~2.3ka between the last two events.In the model,the penultimate event is considered to be recorded in all trenches.As all the three trenches are located at north part of the Puxiong Fault whose strike is apparently different from the south part,the~57km long north secondary segment is supposed to be the seismogenic structure of the paleoearthquake.According to the empirical scaling laws between magnitude and rupture length,the magnitude of the surface ruptured paleoearthquake is estimated to be more than M7 with the coseismic displacement~3.5m.However,the difference between the time of the paleoearthquake events on the middle and south segments of DFZ illustrates their independence as earthquake fracture units,and furthermore,the lower connectivity and the new generation of DFZ.     

The Research of the Activity of the Piedmont Fault on the Tangshankou Segment of the Yuguang Basin Southern Marginal Fault

The Yuguang basin is a half-graben basin in the basin-range tectonic zone in northwest Beijing, located at the northern end of the Shanxi graben system, and the Yuguang basin southern marginal fault (YBSMF) controls the formation of this basin. A linear fault escarpment has formed in the proluvial fan on the piedmont fault zone of the Tangshankou segment of YBSMF. A trench across this escarpment reveals three paleo-earthquake events on two active faults. One fault ruptured at about 9ka for the first time, and then faulted again at about 7.3ka, causing the formation and synchronous activity of another fault. Finally, they faulted for the third time, but we cannot determine the faulting time due to the lack of relevant surface deposition. The accumulative vertical displacement of these three events is about 8.1m. We estimate that the average recurrence period of the piedmont fault is about 1.7ka, and the average slip rate of the piedmont fault is about 1.6mm/a. We also estimate the reference magnitude of each event according to the empirical formula.