诸广花岗岩体放射性水异常的某些特征     

吴敬炳 《华东地质学院学报》1986,(2)

本文以寻找铀矿为目的,在该岩体140Km~2面积上进行水化学普查,发现水异常370个,其特征为:若异常多且成片出现,则预示着有单个矿体规模不大的矿体群存在;条带状展布的水异常预示着存在方向相同的矿化带;阻水阻气构造带近旁之异常预示水源上方存在矿化;水温偏高之水异常与矿化关系密切;与矿化有关的多为铀—氡混合异常;大构造处之水异常并不表示此构造存在矿化,面往往是在其附近次一级构造中成矿.  相似文献   

Late Quaternary-Holocene lake-level changes in the eastern margin of the Thar Desert,India     

Hema Achyuthan  Amal Kar  Chris Eastoe 《Journal of Paleolimnology》2007,38(4):493-507

A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing water. At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year BP). Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between 9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year. These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake brine for manufacturing salt.  相似文献   

某隔震结构动力特性的理论分析与脉动测试   总被引：1，自引：1，他引：1  

贾洪  徐茂义  闫维明  李振宝 《震灾防御技术》2007,2(4):384-390

本文针对国内最大单体隔震建筑建立了SAP2000三维分析模型,并进行了动力特性的理论分析;现场对实际建筑进行了平移振动、扭转振动、垂直振动和平面内弯曲4个方面的脉动测试。利用工程振动反演理论分析了该结构的固有频率、振型、阻尼等动力特性,将实测结构动力特性与理论分析结果进行比较,详细分析实测结果与理论结果差别的原因,并据此对理论模型进行修正,为今后类似结构的设计积累了资料。  相似文献   

基于等高线数据的地性线追踪技术研究   总被引：11，自引：0，他引：11  

王耀革  王玉海 《测绘工程》2002,11(3):42-44

通过研究特征点的提取技术和建立系统的特征点匹配的数学模型，研究了基于矢量等高线数据的地性线的自动追踪技术，利用所述方法，提取的特征点完整，准确；理论和实验表明，所建立的数学模型简捷，实用，有可靠的数学理论基础，且地性线追踪效果良好。  相似文献   

雷达图像中的转换构造信息及其应用     

石火生  林珲  王长林 《遥感学报》2002,6(6):517-522

低序次断裂是地壳变形的直接产物，具有丰富的构造变形信息，经过转换的低序次构造。形式多样，图案复杂，是构造研究的重要对象，也是地表稳定性研究的重要基础。利用香港地区航空雷达图像资料，提取其中低序次构造的弱信息，建立转换变形模型，以分析区内不稳定地表的构造背景。区内北东向断裂是主要构造，其右行剪切形成一系列低序次R面，P面，R^1面构造，在雷达图像上表现为线性弱信息并且与微地貌发育有关。利用线性构造增强，提取技术和低序次构造组合分析方法，结合野外地质调查，确定马鞍山地区EW向的张性破裂是NE向张剪断裂的转换，是造成马鞍山滑坡的重要地质因素。  相似文献   

贵池铜山铜矿床成因探讨   总被引：6，自引：6，他引：6       下载免费PDF全文

俞沧海 《地质与勘探》2001,37(2):12-16

铜山铜矿床矿化类型可划分为层状含铜黄铁矿型，含铜角砾岩型，含铜夕卡岩型和含铜班岩型，控矿因素为地层，岩浆岩及构造，其中层间断裂与接触带构造是主要的容矿构造，铅，硫，氢，氧同位素特征及成矿温度研究表明矿物质和热液主要来源于铜山岩体，矿床成因为层控夕卡岩型铜矿床。  相似文献   

帕米尔东北缘及塔里木盆地西北部弧形构造的扩展特征   总被引：15，自引：0，他引：15  

沈军  汪一鹏  赵瑞斌  陈杰  曲国胜 《地震地质》2001,23(3):381-389

归纳了帕米尔东北缘弧形构造的基本特征 ,分析了塔里木盆地西北部EW向逆断裂背斜带与NNW向隐伏走滑断裂之间的关系。通过塔里木盆地与西南天山和帕米尔东北缘变形特征的对比 ,认为塔里木盆地西北部的变形样式与帕米尔东北缘的弧形构造类似 ,弧形构造具有由帕米尔东北缘向塔里木盆地扩展的特征 ,这种构造是帕米尔向北挤入运动所特有的变形样式  相似文献   

Wave propagation in a seven-story reinforced concrete building: I. Theoretical models     

M. I. Todorovska  S. S. Ivanovi  M. D. Trifunac 《Soil Dynamics and Earthquake Engineering》2001,21(3):705

For transient, high frequency, and pulse like excitation of structures in the near field of strong earthquakes, the classical design approach based on relative response spectrum and mode superposition may not be conservative. For such excitations, it is more natural to use wave propagation methods. In this paper (Part I), we review several two-dimensional wave propagation models of buildings and show results for theoretical dispersion curves computed for these models. We also estimate the parameters of these models that would correspond to a seven-story reinforced concrete building in Van Nuys, California. Ambient vibration tests data for this building imply vertical shear wave velocity β_z=112 m/s and anisotropy factor β_x/β_z=0.55 for NS vibrations, and β_z=88 m/s and β_x/β_z=1 for EW vibrations. The velocity of shear waves propagating through the slabs is estimated to be about 2000 m/s. In the companion paper (Part II), we estimate phase velocities of vertically and horizontally propagating waves between seven pairs of recording points in the building using recorded response to four earthquakes.  相似文献   

Pounding of structures modelled as non‐linear impacts of two oscillators     

K. T. Chau  X. X. Wei 《地震工程与结构动力学》2001,30(5):633-651

A new formulation is proposed to model pounding between two adjacent structures, with natural periods T₁ and T₂ and damping ratios ζ₁ and ζ₂ under harmonic earthquake excitation, as non‐linear Hertzian impact between two single‐degree‐of‐freedom oscillators. For the case of rigid impacts, a special case of our analytical solution has been given by Davis (‘Pounding of buildings modelled by an impact oscillator’ Earthquake Engineering and Structural Dynamics, 1992; 21 :253–274) for an oscillator pounding on a stationary barrier. Our analytical predictions for rigid impacts agree qualitatively with our numerical simulations for non‐rigid impacts. When the difference in natural periods between the two oscillators increases, the impact velocity also increases drastically. The impact velocity spectrum is, however, relatively insensitive to the standoff distance. The maximum relative impact velocity of the coupled system can occur at an excitation period T_n^* which is either between those of the two oscillators or less than both of them, depending on the ratios T₁/T₂ and ζ₁/ζ₂. Although the pounding force between two oscillators has been primarily modelled by the Hertz contact law, parametric studies show that the maximum relative impact velocity is not very sensitive to changes in the contact parameters. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

ENSO循环的数值模拟──Ⅰ:水平结构演变     

杨修群  谢倩 《气象学报》1996,54(1):42-52

利用发展的包含海洋表面边界展和大气辐合反馈过程的热带太平洋海气耦合距平模式，对ＥＮＳＯ循环进行了模拟。通过３０ａ积分，用合模式所展示的热带太平洋海气耦合系统的ＥＮＳＯ循环的水平结构演变特征和观测事实甚为一致，成功地模拟出了ＥＮＳＯ循环的冷暖态的发生发展、衰亡及相互转换等各个位相的动力和热力场的水平结构及其对季节循环的依赖性特征。本文数值模拟结果表明，ＥＮＳＯ循环的主要动力学过程可由热带海气相互作用系统自身所确定。ＥＮＳＯ循环的正确模拟是揭示其形成机制的前提。  相似文献