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991.
992.
Passive seismic techniques have revolutionarised seismology,leading for example to increased resolution in surface wave tomography,to the possibility to monitor changes in the propagation medium,and to many new processing strategies in seismic exploration.Here we review applications of the new techniques to a very particular dataset,namely data from the Apollo 17 lunar network.The special conditions of the lunar noise environment are investigated,illustrating the interplay between the properties of the noise and the ability to reconstruct Green's functions.With a dispersion analysis of reconstructed Rayleigh waves new information about the shallow shear velocity structure of the Moon are obtained.Passive image interferometry is used to study the effect of temperature changes in the subsurface on the seismic velocities providing direct observation of a dynamic process in the lunar environment.These applications highlight the potential of passive techniques for terrestrial and planetary seismology. 相似文献
993.
This paper examined sequence‐stratigraphic features of a gravelly fluvial system of the Iwaki Formation, which developed in a forearc‐basin setting in Northeast Japan during the Eocene through Oligocene. On the basis of three‐dimensional architectural element analysis, we discriminated three major cycles of channel complexes, which contain ten component channel deposits in total in the fluvial succession. Component channel deposits in the uppermost part of each cycle are sandier and associated with overbank muddy deposits and coal beds as compared with those in the lower part of the cycle. Mean clast‐size also decreases upsection in the entire gravelly fluvial deposits. The fluvial succession is interpreted to have been deposited in response to an overall rise in relative sea level that was superimposed by three short‐term relative sea‐level rises on the basis of vertical stacking patterns and component lithofacies features of channel deposits, and of correlation of the fluvial succession with an age‐equivalent marine succession in an area about 50 km offshore. However, geometry and stacking patterns of the channel complexes do not exhibit any distinct temporal variation and amalgamated channel and bar deposits are dominant throughout the transgressive fluvial succession. On the other hand, an overall fining‐upward pattern of the entire Iwaki Formation fluvial deposits in association with three component fining‐upward patterns is distinct, and is interpreted to be consistent with the tenet of the standard fluvial sequence‐stratigraphic models. This indicates that the present example represents one type of variation in the standard fluvial sequence‐stratigraphic models, possibly reflecting the forearc‐basin setting, which is generally represented by higher valley slope, higher shedding of coarse‐grained sediments, and shorter longitudinal profiles to the coastal area as compared with a passive‐continental‐margin setting. 相似文献
994.
Bertrand?GuillierEmail author Jean-Luc?Chatelain Hugo?Perfettini El?Hadi?Oubaiche Christophe?Voisin Rabah?Bensalem Djamel?Machane Mustapha?Hellel 《Bulletin of Earthquake Engineering》2016,14(8):2213-2227
Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature. 相似文献
995.
Soil erosion and its response to the changes of precipitation and vegetation cover on the Loess Plateau 总被引:8,自引:2,他引:6
Soil erosion is a major threat to our terrestrial ecosystems and an important global environmental problem. The Loess Plateau in China is one of the regions that suffered more severe soil erosion and undergoing climate warming and drying in the past decades. The vegetation restoration named Grain-to-Green Program has now been operating for more than 10 years. It is necessary to assess the variation of soil erosion and the response of precipita- tion and vegetation restoration to soil erosion on the Loess Plateau. In the study, the Revised Universal Soil Loss Equation (RUSLE) was applied to evaluate annual soil loss caused by water erosion. The results showed as follows. The soil erosion on the Loess Plateau between 2000 and 2010 averaged for 15.2 t hm-2 a 1 and was characterized as light for the value less than 25 t hm-2 a-1. The severe soil erosion higher than 25 t hm-2 a-~ was mainly distributed in the gully and hilly regions in the central, southwestern, and some scattered areas of earth-rocky mountainous areas on the Loess Plateau. The soil erosion on the Loess Plateau showed a deceasing trend in recent decade and reduced more at rates more than 1 t hm 2 a 1 in the areas suffering severe soil loss. Benefited from the improved vegetation cover and ecological construction, the soil erosion on the Loess Plateau was significantly declined, es- pecially in the east of Yulin, most parts of Yah'an prefectures in Shaanxi Province, and the west of Luliang and Linfen prefectures in Shanxi Province in the hilly and gully regions. The variation of vegetation cover responding to soil erosion in these areas showed the relatively higher contribution than the precipitation. However, most areas in Qingyang and Dingxi pre- fectures in Gansu Province and Guyuan in Ningxia Hui Autonomous Region were predomi- nantly related to precipitation. 相似文献
996.
砂土液化大变形本构模型的三维化及其数值实现 总被引:2,自引:0,他引:2
基于砂土液化大变形机理和适用于二维条件的边界面弹塑性本构模型,发展了符合三维应力空间中边界面和剪胀面上的应力映射规则,建立了三维应力空间中砂土液化大变形本构模型.针对模型特点采用半显式的Cutting Plane算法进行应力积分,并采用Pegasus求根算法根据映射规则计算边界面上的应力映射点,在OpenSees开源有限元平台上实现了三维模型的数值化.结合完全耦合的u-p格式有限元单元,对饱和砂土不排水循环扭剪试验进行了模拟,并进行了一个真三维倾斜地基的动力反应分析.计算结果表明模型和所采用的数值算法具有很好的模拟和分析三维条件下砂土液化后大变形的能力. 相似文献
997.
滑坡稳定性评价中地震作用力计算的讨论 总被引:1,自引:0,他引:1
阐述了目前国内外在滑坡地震稳定性评价方面的理论研究成果和实际应用情况,指出地质矿产行业规范在采用静力法计算地震力时没有乘以0.25的综合影响系数,和其它规范的差别是巨大的.分析后认为这个规定是值得商榷的.最后根据宏观震害现象提出易引起滑坡的地质情况并对其进行了分析,为滑坡治理工程设计和以后的规范修编提供了方法和思路. 相似文献
998.
不同掏蚀深度下古城墙的稳定性数值分析 总被引:1,自引:0,他引:1
以浙江良渚古城的宽顶古场面墙稳定性问题为研究对象,本文针对古城墙可能出现的不同深度的风沙掏蚀的实际工况,通过有限差分软件FLAC3D,建立计算模型进行了稳定性分析,探讨了不同掏蚀深度下城墙破坏机理和规律.研究表明:当城墙墙根掏蚀深度不是很大时,城墙整体稳定,土体开始出现比较小的位移量,掏蚀部位及其周围出现局部塑性破坏现象.随着掏蚀深度的增加,城墙塑性破坏区域不断向城墙体内部、顶部及顶部后缘范围发展,城墙上的土体位移量随着掏蚀深度的增加而呈数量级的增加,直至城墙出现整体崩塌破坏.掏蚀作用加剧了地震作用下城墙体的破坏,在掏蚀部位形成潜在破坏口,内部形成塑性贯通区,造成墙体整体崩塌. 相似文献
999.
1000.
根据近场强震台加速度记录对2011年10月12日北京市石景山区ML2.1地震的加速度影响场进行了计算分析.同时使用了首都圈宽频带数字台站记录数据通过P波初动格点尝试法解算出该地震的震源机制解,并与加速度影响场进行对比研究.结果表明,此次地震加速度影响场水平向加速度高于垂直向;水平向峰值加速度分布区和加速度影响场高低速度过渡区总体呈EW向或NEE向分布,与震源机制解结果的两个节面走向较为一致;加速度衰减NS向快于EW向.本文研究结果可为强震或较大地震发生后快速判定震害影响场提供参考依据. 相似文献