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61.
Jean-François Semblat Roberto Paolucci Anne-Marie Duval 《Comptes Rendus Geoscience》2003,335(4):365-370
For the analysis of seismic wave amplification, modal methods are interesting tools to study the modal properties of geological structures. Modal approaches mainly lead to information on such parameters as fundamental frequencies and eigenmodes of alluvial basins. For a specific alluvial deposit in Nice (France), a simplified modal approach involving the Rayleigh method is considered. This approach assumes a set of admissible shape functions for the eigenmodes and allows a fast estimation of the fundamental frequency of the basin. The agreement with other numerical results (Boundary Element Method) and experimental ones is fully satisfactory. The simplified modal method then appears as an efficient mean for the global vibratory characterization of geological structures towards resonance. To cite this article: J.-F. Semblat et al., C. R. Geoscience 335 (2003). 相似文献
62.
The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system.
Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case
the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz.
The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic
zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing
type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that
these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent
low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of
this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type
A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there
were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important
chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun
Early Paleozoic.
Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program
“ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National
Geological Surveying Bureau. 相似文献
63.
Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China) 总被引:21,自引:0,他引:21
Dan-Ping Yan Mei-Fu Zhou Hong-Lin Song Xin-Wen Wang John Malpas 《Tectonophysics》2003,361(3-4):239-254
In the Yangtze Block (South China), a well-developed Mesozoic thrust system extends through the Xuefeng and Wuling mountains in the southeast to the Sichuan basin in the northwest. The system comprises both thin- and thick-skinned thrust units separated by a boundary detachment fault, the Dayin fault. To the northwest, the thin-skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast. The former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines. Thrust detachments occur along Silurian (Fs) and Lower Cambrian (Fc) strata and are dominantly associated with the anticlines. To the southeast, this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along Silurian (Fs), Cambrian (Fc) and Lower Sinian (Fz) strata. There are, however, numerous secondary back thrusts. Therefore, the thin-skinned belt is like the Valley and Ridge Province of the North American Applachian Mountains. The thick-skinned belt structurally overlies the thin-skinned belt and is characterized by a number of klippen including the Xuefeng and Wuling nappes. It is thus comparable to the Blue Ridge Province of Appalachia.The structural pattern of this thrust system in South China can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution. The system was developed through a northwest stepwise progression of deformation with the earliest delamination along Lower Sinian strata (Fz). Analyses of balanced geological cross-sections yield about 18.1–21% (total 88 km) shortening for the thin-skinned unit and at least this amount of shortening for the thick-skinned unit. The compressional deformation from southeast to northwest during Late Jurassic to Cretaceous time occurred after the westward progressive collision of the Yangtze Block with the North China Block and suggests that the orogenic event was intracontinental in nature. 相似文献
64.
65.
2002年春末夏初一次新的厄尔尼诺事件形成;1~12月北半球大气环流的主要特征表现为:中纬度地区纬向环流盛行,西太平洋副热带高压持续偏强偏西,我国大部地区气温偏高,降水呈南多北少分布;欧亚地区夏季500hPa位势高度距平场上,中高纬从西到东呈现为“ - ”分布形式,贝加尔湖地区为正距平中心,7月在贝加尔湖地区出现典型阻高;东亚夏季风偏强,南亚夏季风及热带对流指数偏弱;夏季赤道辐合带偏弱等。在上述大气环流的影响下,我国的天气气候发生了异常。 相似文献
66.
太平洋混合层厚度(dml)年际异常的初步分析 总被引:1,自引:0,他引:1
用太平洋区域30a逐月混合层厚度(dml)及浅层海温(Ts)距平资料,分析了20°S以北太平洋区域dml年际变率的地理分布和季节变化,得到两个纬向dml高变率带,它们分别位于北太平洋(45°N附近)和赤道中、西太平洋.重点分析了赤道太平洋dml高变率带,并对其上混合层气候位置、dml年际异常与El Nino事件关系及伴随强El Nino事件的dml正异常东传等作了初步分析. 相似文献
67.
Hilbert-Huang变换在密频结构阻尼识别中的应用 总被引:14,自引:3,他引:14
Hilbert—Huang变换是一种新的数据处理方法,由经验模分解(Empirical Mode Decomposition)技术及Hilbert变换两部分组成。本文研究此方法对于密频结构阻尼识别的应用。首先对于两自由度系统模型,说明该方法用于阻尼识别的步骤。进而研究存在频率密集现象的高层建筑的阻尼识别问题。上述结果与理论值及由半功率带宽法的识别值进行了比较,对比显示Hilbert.Huang方法较传统方法具有良好的识别密频结构阻尼的性能,适用于大型结构的系统识别。 相似文献
68.
分析了1900年以来长江3次巨洪的3个强信号:(1)太阳黑子活动,(2)厄尔尼诺事件,(3)青藏高原南部大震,它们对大气环流异常的影响分别称为日气作用、海气作用、地气作用,依据长江巨洪和3个强信号的基本事实,讨论了长江发生巨洪的统计规律,指出当3个强信号的出现时间互相重叠时,长江很可能发生巨洪,如果再叠加其它信号,长江发生巨洪的量级更大,这对长江巨洪的超长期预期具有重要的指示作用。 相似文献
69.
地震模拟振动台振动对建筑物中人体的舒适感的影响分析 总被引:1,自引:0,他引:1
本文给出了一种地震模拟振劝台振运对建筑物中人体的舒适感影响的分析方法,并结合实例进行了具体分析。文中给出的分析方法和实例计算结果对于地震馆的设计有一定参考价值。 相似文献
70.
对东北输油管道锦县,盖县,海城段的粉土细砂,中砂,粉砂进行了振动液化试验,取得了和类土的τd-logNf曲线,τd/σ′-logNf曲线,为在以上地区进行液化判别提供了重要的基础资料,同时也为研究其它的地区相同土质的振动性能提供借鉴。 相似文献