长山群岛海岸地貌特征及其地震地质意义

本文根据长山群岛31条海岸阶地剖面资料进行统计分析,认为本区普遍存在Ⅰ-Ⅴ级海蚀阶地,时代为更新世;存在一级堆积阶地,时代为全新世中期:存在三级沿岸堤,时代为全新世中、晚期.根据这些海岸地貌的对比分析,认为新生代以来本区为构造上升区,与辽东半岛皮口—庄河—大孤山段海岸地貌特征和新构造运动特征一致,其间庄河断裂无明显活动,同属于辽东隆起带:还认为长山群岛的东区比西区上升较快,东区地震活动性较高.     

六盘山断裂带构造活动特征及流域盆地地貌响应

通过航卫片解译和野外实地调查,对六盘山断裂带新活动特征开展详细研究。调查发现六盘山东麓断裂为一条全新世活动的逆左旋走滑断裂,而六盘山西麓断裂为晚更新世活动的挤压逆冲断裂,二者的构造活动控制和影响了本区的地貌发育和地震活动。同时利用SRTM数据提取六盘山东西两侧泾河和水洛河上游流域盆地水系,得到流域盆地面积-高程积分值(HI值)分布图,探讨本区活动构造和地貌的响应关系。分析结果表明,在相同的岩性条件下六盘山东侧的HI值要低于西侧,反映了活动断裂对本地区地貌演化特征的不同影响。上述地貌分析研究为认识和理解六盘山地区地貌演化以及控制因素提供了基础数据和思路。     

玉门塔尔湾北西向地貌陡坎成因探讨

运用探槽开挖,揭露还原构造运动的方法,对沿塔尔湾断裂分布的地貌陡坎的形成过程进行了分析,得出了塔尔湾断裂的主要活动时期为早中更新世,现在地貌上的陡坎是外动力作用形成的,不是断裂活动形成的结论。     

云南省通海-石屏地区地震构造

本文采用地貌分析法确定了云南省通海—石屏地区第四纪中的地表垂直构造形变。应用这个形变资料,根据弹性位错理论求得区内几条活动断层的错距,其中曲江断裂的右旋水平错距为5公里。指出本区在第四纪中主要受北北西—南东东方向的压应力作用。根据地震裂缝、三边测量、定点基线测量和震源机制资料,求得本区现代构造应力场。作者发现它与第四纪构造应力场是相似的。由曲江断裂的平均5—7毫米/年的水平运动速度去估计,通海7.7级地震平均复发周期为300—400年。作者还指出通海地震前400年内,地震活动形成空区。并利用围空地震资料,求得空区内地震震级M与围空地震的断层总面积S之间存在经验关系, M=1gs-3.8     

宁夏沙坡头黄河大弯的成因分析

黄河在宁夏沙坡头形成了"几"字形河曲地貌,并在河曲凸岸发育了3级河流阶地。本文针对沙坡头大弯河流阶地特征、阶地年龄,以及大拐弯的成因进行了分析,探讨本区地貌发育的机制。结果表明:(1)沙坡头大弯3级河流阶地形成的主要原因是构造抬升作用,气候变化对此处阶地形成的作用不明显。在区域新构造活动强烈的背景下,约中更新世末期中卫盆地开始抬升,黄河河道被固定,河流下切形成本区的最高阶地T3;约在70kaB.P.、8kaB.P.形成T2、T1阶地。(2)沙坡头黄河大拐弯是由香山—天景山断裂左旋走滑位错,以及水流受地球自转偏向力的河流内生动力共同作用的结果,并且河流的内生动力作用远大于前者的贡献。     

福建龙海-漳浦沿海活动断裂与火山活动

文中通过福建龙海—漳浦沿海主要断裂的玄武岩喷发,断裂两侧第四纪以来形成的地貌面和海相地层的差异性变化等特点,分析了断裂晚第四纪以来的活动特征及断裂构造的组合特征。研究结果表明:龙海流会-漳浦将军澳断裂在新近纪—第四纪晚更新世早期 (N2—Q3p)有玄武岩多次循其喷发,晚更新世(Q3p)活动明显,属晚更新世活动断裂;龙海港尾 -漳浦湖西断裂亦属晚更新世(Q3p)活动断裂,断裂下盘上升速率为 1. 11mm/a。这 2条断裂将本区切割形成港尾地堑、南太武山地垒、流会-将军澳以东海域地堑     

福建沿海地区晚更新世以来构造地貌发育与构造应力场

一、福建沿海地区构造地貌发育基础与构造地貌特征福建沿海地区地处欧亚板块东南缘,在漫长的地质发展史中,由于欧亚板块,太平洋板块和菲律宾板块的相互作用,燕山运动以前,本区是一个长期隆起的剥蚀区,有人称其为“闽东滨海加里东隆起带”或“闽东滨海台拱”。而中生代晚期所发生的以断裂构造为主要形式的燕山运动,则为本区地质构造发展史上一次强烈的大规模地壳运动,它对本区地壳构     

福建沿海地区断裂近期活动性与地震

福建沿海地区断裂构造发育,有北北东—北东向,北西向、东西向、南北向及环状或弧形断裂等构造系。近期以北北东—北东向压扭性断裂和北西向张扭性断裂活动性最强。它们控制着本区海岸地貌的发育以及地震的发生和分布。本文拟根据地壳垂直形变及海平面变化的资料,讨论本区有强震产生的活动断裂与地震活动。     

用模式识别方法确定北京及其邻近地区易发生地震的地点

本文研究了北京及其邻近地区的地质,地貌,地球物理等特征并对有关特征进行了模式识别。结果表明本区易发生地震的地点主要与主活动断裂及新生代断陷盆地有关,且活动断裂数目愈多,判定为强震可能发生地点的概率就愈大。地形高差似乎与本区强震发生的地点无关。FH实验,即未来历史实验(future history test)结果表明:预测是成功的,1882年至1983年中发生了M6.0地震的五个地区均被识别为未来可能发生强震的地点。      

青藏高原的现代构造运动、地震线及地震幕

据青藏高原的构造背景、现代构造、地理、地貌及地震活动特征划分成如下三个分区:1.喜马拉雅;2.羌塘高原;3.柴达木盆地。本区存在着弧形地震线,NE和NW向地震线及NS向的中轴地震线,是地壳中上部脆性破裂及断裂粘滑运动的表现。对1897—1980年本区的强震活动进行了分幕,初步分析了各地震幕的动力学意义。     

Progressive changes in the morphology of fluvial terraces and scarps along the Rappahannock River,Virginia

Progressive geomorphic changes in the flight of fluvial terraces along the Rappahannock River, Virginia, provide a framework for analysing the effect of time on landforms. The oldest terrace is probably no younger than early Quaternary, and the youngest major fill terrace probably correlates with the high sea level of the last major interglacial. A uranium-series date of 187,000 yr has been obtained on coral from marine sediments related to this terrace. Indices of terrace preservation, especially drainage densities and area to perimeter ratios, show systematic changes with terrace age. Hence, these variables appear to satisfactorily indicate relative age, and could perhaps be used to estimate actual ages if suitably calibrated. The morphology of scarps formed by entrenchment of the fluvial terraces is more variable than analogous morphology of fault scarps and wave-cut bluffs. However, measurements of the fluvial scarps clearly indicate that for a given terrace age, higher scarps tend to have steeper slopes, and that for a given scarp height, older scarps tend to have gentler slopes. The terrace forms themselves are preserved for at least several million years. Depositional features such as bars and channels with l–3m of relief are preserved on terraces on the order of 10⁵ yr old. Scarps related to the formation of terraces of this age are well preserved and have slopes of about 6–8 degrees where the scarp height is about 5 m. The preservation of fluvial landforms and scarps suggests that, if fault scarps comparable to these features were commonly formed by earthquakes in low relief areas of the eastern United States, many should be recognizable.     

闽粤沿海全新世垂直构造运动的速率

基于华南地区新构造运动具有断块垂直差异运动的特征,本文主要根据目前已测定的,分布于闽粤沿海地区的若干个全新世海相沉积物的放射性年代,海拔高度等数据,初步估算和对比闽粤沿海不同断块构造区的垂直构造运动的速率,并探讨它与地震活动的关系     

ANALYSIS OF THE LATE QUATERNARY ACTIVITY ALONG THE WENCHUAN-MAOXIAN FAULT -MIDDLE OF THE BACK-RANGE FAULT AT THE LONGMENSHAN FAULT ZONE

The Longmenshan fault zone is located in eastern margin of Tibetan plateau and bounded on the east by Sichuan Basin, and tectonically the location is very important. It has a deep impact on the topography, geomorphology, geological structure and seismicity of southwestern China. It is primarily composed of multiple parallel thrust faults, namely, from northwest to southeast, the back-range, the central, the front-range and the piedmont hidden faults, respectively. The M_S8.0 Wenchuan earthquake of 12^th May 2008 ruptured the central and the front-range faults. But the earthquake didn't rupture the back-range fault. This shows that these two faults are both active in Holocene. But until now, we don't know exactly the activity of the back-range fault. The back-range fault consists of the Pingwu-Qingchuan Fault, the Wenchuan-Maoxian Fault and the Gengda-Longdong Fault. Through satellite image(Google Earth)interpretation, combining with field investigation, we preliminarily found out that five steps of alluvial platforms or terraces have been developed in Minjiang region along the Wenchuan-Maoxian Fault. T₁ and T₂ terraces are more continuous than T₃, T₄ and T₅ terraces. Combining with the previous work, we discuss the formation ages of the terraces and conclude, analyze and summarize the existing researches about the terraces of Minjiang River. We constrain the ages of T₁, T₂, T₃, T₄ and T₅ surfaces to 3~10ka BP,~20ka BP, 40~50ka BP, 60ka BP and 80ka BP, respectively. Combining with geomorphologic structural interpretation, measurements of the cross sections of the terraces by differential GPS and detailed site visits including terraces, gullies and other geologic landforms along the fault, we have reason to consider that the Wenchuan-Maoxian Fault was active between the formation age of T₃ and T₂ terrace, but inactive since T₂ terrace formed. Its latest active period should be the middle and late time of late Pleistocene, and there is no activity since the Holocene. Combining with the knowledge that the central and the front-range faults are both Quaternary active faults, the activity of Longmenshan fault zone should have shifted to the central and the front-range faults which are closer to the basin, this indicates that the Longmenshan thrust belt fits the "Piggyback Type" to some extent.     

河西走廊榆木山前土壤发育特征及其随时间的演变关系

在河西走廊榆木山前开展了旨在用于活动构造测年工作的土壤发育年代学新方法的研究。通过在不同时代河流阶地上开挖土壤探槽,系统采集土壤样品并进行化学成分分析,以及对各级河流阶地形成年代的＾１４Ｃ和热释光年龄测定,详细研究了该区与断层新活动有关的土壤发育的主要物理和化学特性及其随时间（年代）的演变规律,初步建立起了土壤ＣａＣＯ３含量和ＣａＣＯ３累积指数数值与发育年代之间的定量计算关系式,经回检和对比分析认     

西南天山柯坪塔格前缘断裂带东段晚第四纪活动特征

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     

华山山前断裂中段晚第四纪活动的地貌表现及响应

调查了华山山前断裂中段（石堤峪-杜峪）晚更新世以来,尤其是全新世以来的断层构造地貌,讨论了它们的成因、特点及对断裂活动的响应关系。断层构造地貌主要包括：断层三角面、断层陡坎、洪积阶地、埋藏型洪积扇以及冲沟裂点。对各大沟峪峪口的洪积阶地进行了大比例尺微地貌测量,并在部分沟峪两侧沿断层崖陡坎及冲沟沟床布置了测线。结合T1、T2级洪积阶地位错测量结果及其14C年龄计算得到,华山山前断裂中段6000a-2000aB.P.的垂直滑动速率为1.485mm/a;2000aB.P.以来的垂直滑动速率为3.73mm/a。最后结合野外调查与理论认识,建立了正断层作用下洪积阶地与埋藏型洪积扇的演化模式。本研究结果支持华山山前断裂是1556年华县814级地震发震构造的观点。     

青海大通宝库河断裂活动性研究

本文在对宝库河地区第四系及地貌单元划分对比的基础上，结合年代测试结果，分析了宝库河断裂带的断错微地貌特征。结果表明，宝库河断裂穿过的Ⅰ－Ⅲ级冲积、坡洪积阶地未被断错；经热释光年代测定，至少在距今６．６±０．８万年以来该断裂未再活动过，是一条晚更新世早期断裂，属左旋走滑型兼具挤压逆冲特性。     

元谋断裂北段的新活动与地震危险程度

元谋断裂有强烈、复杂和多阶段的新活动,表现西盘先断陷成湖,后回升成阶地,并在东盘水平挤压下时而顺扭、时而反扭,使阶地变形、错位、掀斜,并在湖积中形成轴向或走向与主干断裂成向南或向北锐角相交的新褶皱与断层,构成新“人”字形构造。 此带地处滇西南北带中段,灾害性地震危情不如南、北两端严重     

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

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.     

The headward extent of fluvial landforms and associated vegetation on massanutten mountain,Virginia

Variation in fluvial landforms and associated vegetation in the headward (upstream) direction has received little study and the controlling factors are not well understood. The relations among channel gradient, basin area, stream order, and the headward extent of fluvial landforms and vegetation was studied in 18 small basins and larger nearby stream reaches in the Massanutten Mountain area, northern Shenandoah Valley, Virginia. Low-order streams were traversed to their basin heads. Notice was made of the point or region of the disappearance of fluvial landforms. Indicator species were used to confirm landform identification. The studied landforms include the channel bar, channel shelf, floodplain, and terraces. Basin geomorphic characteristics were determined from topographic and geologic maps and ground surveys. Results suggest that gradient is the most important factor controlling the development of fluvial landforms. Floodplains have not developed along stream reaches where average channel gradients exceed 0.15. Channel shelves and associated vegetation occur farther upstream than floodplains.