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D. KAO 《Geophysical Prospecting》1982,30(6):866-878
Magnetotelluric response is studied for an inhomogeneous medium having conductivity varying linearly with depth as σ(z) =σ1+αz. For a medium having conductivity increasing linearly with depth, the phase of the impedance approaches 60° at long periods and the apparent resistivity becomes log (ρa) = 2 log (1.36/α1/3) — 1/3 log (T'). The asymptote of log (ρa, T'→∞) when plotted against log (T') has a constant gradient —1/3 and has an intercept on the log (T') axis, which equals 6 log (1.36/α1/3). When a homogeneous layer with a moderate thickness overlies an inhomogeneous half-space, this layer does not affect the asymptote, but it affects the cut-off period and pushes this toward the long period direction. For a medium having conductivity decreasing linearly with depth, the impedance is equivalent to that of a Cagniard two-layer model; the intercept period related to the thickness is T'0=σ1(h2/2)2. Homogeneous multilayer approximations to an inhomogeneous layer are also investigated, and it is shown that the fit to the model variation depends on the number of layers and the layer parameters chosen. 相似文献
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微微型浮游植物是水环境生态碳汇的重要基石之一,也是初级生产的重要执行者。选取了一个典型的陆海交界关键带环境——海南东寨港入海口水域,采集了东寨港红树林保护区开阔水域、入港河流和新埠海海端的微微型浮游植物的样品,通过流式细胞仪分析技术对样品进行分析,以探究它们在东寨港水域中的丰度、分布及环境指示意义。结果表明,冬季水域微微型浮游植物以真核浮游植物(Eukaryote,Euk)和聚球藻(Synechococcus,Syn)两大类群为主,其中聚球藻有两个亚群,分别为富含藻蓝蛋白聚球藻(Phycocyanin-rich,PC)和富含藻红蛋白聚球藻(Phycoerythrin-rich,PE)。Syn-PC、Syn-PE和Euk在东寨港水域表层水体的平均丰度分别为(2.61×104±1.09×104)、(3.06×104±7.05×103)、(1.56×105±8.03×104) cells/m L,底层水体的平均丰度分别为(2.64×104±... 相似文献
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西昆仑—塔里木—天山岩石圈深地震探测综述 总被引：40，自引：6，他引：40
沿新疆地学断面走廊域实施了3种深地震探测方法：近垂直深地震反射剖面、宽角反射与折射深地震测深剖面和移动式宽频地震观测，揭露出西屁仑-塔里木-天山岩石圈的结构与横向变化，发现了塔里木大陆地块与青藏高原西北部西昆仑造山带碰撞的地震学证据，揭示出天山与塔里木、天山与准噶尔，以及昆仑山与塔里木之间的岩石圈尺度盆山耦合关系。阶段成果发表后引起国内外学者广泛注意，本文结合相关资料对这些新成果进行了系统综述，旨在对比研究青藏高原南北两缘不同的碰撞变形之深部过程。 相似文献
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针对一类基于T-S 模糊模型描述的具有输入与状态时滞的不确定系统,研究了保成本控制问题,得到了保成本控制律存在的充分条件,并以线性矩阵不等式的形式给出了控制器的设计方法.最后仿真实例验证了该方法的可行性. 相似文献
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Earthquake-induced potential landslides are commonly estimated using landslide susceptibility maps. Nevertheless, the fault location is not identified and the ground motion caused by it is unavailable in the map. Thus, potential coseismic landslides for a specific fault motion-induced earthquake could not be predicted using the map. It is meaningful to incorporate the fault location and ground motion characteristics into the landslide predication model. A new method for a specific fault motion-induced coseismic landslide prediction model using GIS (Geographic Information System) is proposed herein. Location of mountain ridges, slope gradients over 45 o , PVGA (Peak Vertical Ground Accelerations) exceeded 0.15 g, and PHGA (Peak Horizontal Ground Accelerations) exceeded 0.25 g of slope units were representing locations that initiated landslides during the 1999 Chi-Chi earthquake in Taiwan. These coseismic landslide characteristics were used to identify areas where landslides occurred during Meishan fault motion-induced strong ground motions in Chiayi County in Taiwan. The strong ground motion (over 8 Gal in the database, 1 Gal = 0.01 m/s 2 , and 1 g = 981 Gal) characteristics were evaluated by the fault length, site distance to the fault, and topography, and their attenuation relations are presented in GIS. The results of the analysis show that coseismic landslide areas could be identified promptly using GIS. The earthquake intensity and focus depth have visible effects on ground motion. The shallower the focus depth, the larger the magnitude increase of the landslides. The GIS-based landslide predication method is valuable combining the geomorphic characteristics and ground motion attenuation relationships for a potential region landslide hazard assessment and in disaster mitigation planning. 相似文献
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边缘海氮循环过程研究是全球海洋氮循环研究的重要组成部分,对全球氮源汇格局有显著影响,进而对全球气候变化产生反馈。人为活动和气候变化又是影响边缘海关键氮循环过程速率的重要因素。南海作为中国和西北太平洋最大的边缘海,是边缘海氮循环研究的理想场所。本文详细总结了南海近岸和海盆区的氮源汇过程及其内循环过程的最新研究进展,结果显示人为活动对上述过程的显著扰动。此外,全球变暖和海洋酸化正改变不同的氮循环过程速率,并可能引起南海氮收支平衡的不确定性。文章最后提出了边缘海氮循环研究的重要发展方向。 相似文献
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XIAO Xuchang LIU Xun GAO Rui Houn KAO LUO Zhaohua Institute of Geology Chinese Academy of Geological Sciences Beijing China Institute of Earth Sciences Academia Sini Taipei China China University of Geosciences Beijing China 《《地质学报》英文版》2001,75(2):126-132
New results from deep seismic reflection profiling, wide-angle reflection-refraction profiling and broadband seismic experiments reveal that a series of south-dipping reflectors occur on the southern margin of the Tarim block (basin). However, it is these south-dipping structures that are intercepted by another series of north-dipping reflectors at depths from 30 to about 150 km beneath the foreland of the W Kunlun Mountains. No evidence from the above geophysical data as well as geochemical and surface geological data indicate the southward subduction of the Tarim block beneath the W Kunlun Mountains (NW Tibet plateau), forming the so-called "two-sided subduction" model for the Tibet plateau as proposed by previous studies. So the authors infer that the tectonic interaction between the Tarim block and the W Kunlun block was chiefly affected by a "horizontal compression in opposite directions", which brought about "face-to-face contact" between these two lithospheric blocks and led to the thickening, sh 相似文献