渭河断裂中段最新活动的几个证据     

韩许恒  韩城建 《内陆地震》1993,7(4):363-369

根据渭河断裂中段两侧渭河一二级阶地的高差对比,研究了近20000多年来,特别是近6000多年来渭河断裂中段的活动性,并粗略估算了断裂活动的位移幅度和位移速率。又根据断裂附近探槽揭示的古地震遗迹及历史地震、现代地震沿断裂的分布,认为渭河大断裂为近期活动较强烈的发震断裂。  相似文献   

Bluff evolution and long-term recession rates,southwestern Lake Michigan     

C. W. Rovey II  M. K. Borucki 《Environmental Geology》1994,23(4):256-263

Where eroding cohesive sediments are present, Lake Michigan bluffs range up to 40 m in height, exposing multiple glacial stratigraphic units. Following the model presented here, bluffs form as a wave-cut terrace erodes inland from a point near the original shoreline. The erosion plane is nearly horizontal, in contrast with the eastward dip of the glacial units inherited from underlying bedrock. Therefore, terraces eroding inland produce progressively higher bluffs and expose successively older units at the toe and beneath the lake. This process was repeated several times as lake levels sequentially dropped to their modern stage. The initial modern shoreline, and hence the width of the wave-cut terrace, was determined from four offshore seismic and bottom-sampling profiles. It was picked as an inflection point in the lake bed, occurring offshore of dipping reflectors intersecting the lake bottom. The calculated average recession rate over a 2500-year duration of the modern stage is 1.5 m/yr in contrast to average rates of approximately 0.6 m/yr measured over the last century. Thus rates decrease through time as the terrace widens and wave energy is dampened. By correlating bluff height to recession distance, a third rate of approximately 2.7 m/yr for the first 940 years of recession is calculated from relict Nipissing bluffs. The three rates define a steeply decaying exponential curve in early stages of bluff retreat, flattening into a nearly linear function after 1000 years.  相似文献   

渭河宝鸡段阶地形成时代及地层对比     

方甲炳  李方周 《陕西地质》1993,(2)

渭河宝鸡段阶地共分为5级,第四纪地层自下更新统至全新统均有出露。五级阶地形成于早更新世中晚期,距今约130万年;四级阶地形成于早更新世晚期,距今约85万年;三级阶地形成于早更新世中期,距今约55万年;二级阶地形成于中更新世晚期—晚更新世早期,距今约15～11万年;一级阶地形成于全新世早期,距今约0.8万年。  相似文献   

青海共和至甘肃兰州黄河河谷地貌的形成与青藏高原东北缘隆升的关系   总被引：4，自引：2，他引：2  

赵振明  刘百篪 《西北地质》2003,36(2):1-12

依据共和至兰州黄河河谷大量的实测数据,结合现有的研究成果,认为构造作用对该区河谷地貌的形成起到一定的决定作用。河谷地貌的抬升速率揭示出两次新构造事件：一次发生在20万年B．P．至15万年B．P．;另一次发生在1万年以来。黄河阶地纵剖面反映出青藏高原第四纪挤压力向北东方向逐渐减小,在兰州出现挤压力在某时段消减的情况。  相似文献   

月球地形测绘和月球大地测量(5)   总被引：8，自引：1，他引：8  

陈俊勇 《测绘科学》2004,29(6):7-10

主要介绍月球地形测绘和月球大地测量的情况。第一部分论述了月球大地测量(Selenodesy)的定义和方法。月球大地测量的一个特点是它的观测数据绝大部分都要依靠航天探测器或环月、绕月卫星来获取。月球大地测量的内容可以考虑有三个方面:一是在月球上给出一个有确定定义的坐标参考系,并在其中布测一个控制网;二是确定这一月球参考系的大地测量几何和物理常数;三是求定月球的外部重力场。第二部分介绍月球地形测绘。重点介绍了月球地形的特点,它大体分为月海、月陆、环形山等三种类型。  相似文献   

渭河盆地断层活动的横向迁移   总被引：6，自引：0，他引：6       下载免费PDF全文

冯希杰  戴王强 《地震学报》2004,26(2):174-182

断裂活动的横向迁移是断裂发展演化过程中的一种普遍现象. 在渭河盆地这种现象也较为常见，特征比较典型. 本文以蓝田南侧王顺山山前断裂活动向其北侧的骊山山前断裂和渭南塬前断裂的迁移，骊山凸起西北侧临潼¾长安断裂带内大鲍陂¾牛角尖次级断层的强烈活动向神峪寺¾肖家寨次级断层的迁移，以及渭河盆地中西部宝鸡与泾阳间一系列北西向断裂活动的横向迁移为例，分析和讨论了它们各自的迁移时段及迁移过程，为充分认识这些地区的构造发展和地貌演化历史，深刻把握渭河盆地内最新的控制性活动断裂，更加切近实际地估计每一条断裂的地震危险性提供了帮助.   相似文献   

Landscape disequilibrium on 1000–10,000 year scales Marsyandi River, Nepal, central Himalaya     

Beth Pratt-Sitaula  Douglas W. Burbank  Arjun Heimsath  Tank Ojha 《Geomorphology》2004,58(1-4):223-241

In an actively deforming orogen, maintenance of a topographic steady state requires that hillslope erosion, river incision, and rock uplift rates are balanced over timescales of 10⁵–10⁷ years. Over shorter times, <10⁵ years, hillslope erosion and bedrock river incision rates fluctuate with changes in climate. On 10⁴-year timescales, the Marsyandi River in the central Nepal Himalaya has oscillated between bedrock incision and valley alluviation in response to changes in monsoon intensity and sediment flux. Stratigraphy and ¹⁴C ages of fill terrace deposits reveal a major alluviation, coincident with a monsoonal maximum, ca. 50–35 ky BP. Cosmogenic ¹⁰Be and ²⁶Al exposure ages define an alluviation and reincision event ca. 9–6 ky BP, also at a time of strong South Asian monsoons. The terrace deposits that line the Lesser Himalayan channel are largely composed of debris flows which originate in the Greater Himalayan rocks up to 40 km away. The terrace sequences contain many cubic kilometers of sediment, but probably represent only 2–8% of the sediments which flushed through the Marsyandi during the accumulation period. At 10⁴-year timescales, maximum bedrock incision rates are 7 mm/year in the Greater Himalaya and 1.5 mm/year in the Lesser Himalayan Mahabarat Range. We propose a model in which river channel erosion is temporally out-of-phase with hillslope erosion. Increased monsoonal precipitation causes an increase in hillslope-derived sediment that overwhelms the transport capacity of the river. The resulting aggradation protects the bedrock channel from erosion, allowing the river gradient to steepen as rock uplift continues. When the alluvium is later removed and the bedrock channel re-exposed, bedrock incision rates probably accelerate beyond the long-term mean as the river gradient adjusts downward toward a more “equilibrium” profile. Efforts to document dynamic equilibrium in active orogens require quantification of rates over time intervals significantly exceeding the scale of these millennial fluctuations in rate.  相似文献   

Geomorphologic evidence of phased uplift of the northeastern Qinghai-Tibet Plateau since 14 million years ago   总被引：11，自引：0，他引：11  

LU Huayu  WANG Xiaoyong  AN Zhisheng  MIAO Xiaodong  ZHU Rixiang  MA Haizhou  LI Zhen  TAN Hongbing & WANG Xianyan . State Key Laboratory of Loess  Quaternary Geology  Institute of Earth Environment  Chinese Academy of Sciences  Xi''''an China  . Qinghai Institute of Salt Lakes  Chinese Academy of Sciences. Xining  China  . Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China  . Department of Geography  Qinghai Normal University  Xining  Chi 《中国科学D辑(英文版)》2004,47(9)

~~Geomorphologic evidence of phased uplift of the northeastern Qinghai-Tibet Plateau since 14 million years ago~~  相似文献   

西南天山明尧勒背斜的第四纪滑脱褶皱作用   总被引：3，自引：1，他引：3       下载免费PDF全文

陈杰  Scharer K M  Burbank D W  Heermance R  王昌盛 《地震地质》2005,27(4):530-547

通过对明尧勒活动背斜喀浪勾律克河剖面生长前地层和翼部生长地层几何结构的填图以及变形河流阶地的系统测量,结合磁性地层及释光年代学研究,认为该背斜的滑脱褶皱作用起始于距今约1·6Ma,其总体几何结构形成于褶皱作用的早期,但其生长扩展并不完全遵从自相似性特征。持续的缩短作用部分被褶皱翼部陡倾膝折带的加长所吸收(由此导致背斜波幅的增加),另一部分可能是通过不同时期褶皱翼部不同膝折带组的旋转和迁移来实现的。明尧勒背斜的持续构造抬升是背斜区河流下切形成多级基座阶地的主因。晚第四纪褶皱的生长以背斜的垂直抬升为主,主要集中在北翼近核部,背斜宽度变化不大。背斜不同时期的抬升量和抬升速率均大于其缩短量和缩短速率,表明明尧勒背斜的变形以翼旋转为主(Pobletet al.,1996)。背斜自形成以来缩短速率和抬升速率均有减小的趋势  相似文献   

陕西省数字地震台下方壳幔速度结构研究   总被引：3，自引：1，他引：3  

张学民  刁桂苓  王为民  束沛镒 《华北地震科学》2005,23(2):1-9

利用广义反、透射系数的传递矩阵计算理论地震图，用快速模拟退火法搜索最佳模型，通过与地震台站实际记录的P波波形进行拟合对比，反演了陕西省13个数字地震台下方的P波速度结构。台站分布区域涉及到秦岭造山带、渭河盆地及鄂尔多斯地台三个构造区域。结果显示，3个构造区的地下速度结构差异明显，呈现了各自的构造特点。其中秦岭造山带上地壳乃至地表速度高，中下地壳出现多个低速层，可能与岩石脱水、构造滑脱带等有关；渭河盆地内上中地壳高低速度层交替出现，反映了断层活动在浅部的影响；鄂尔多斯地台有部分台站保持稳定的匀速构造。反映了古老地台地层稳定发展的特性，部分台站受到后期改造，低速层位增多。因为变化剧烈的台站分布在盆地的南部和西部。而且震源机制解显示该区主应力场方向为近东西向，可以说秦岭北缘的断裂作用以及后来来自青藏高原的挤压应力是导致渭河盆地形成和发展的主要因素。最后我们讨论了速度结构与强震、地震分布以及不同构造演化的关系。  相似文献