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Summary The object of the present paper is to investigate magneto-elastic waves and disturbances in initially stressed conducting media. Firstly, the theory of magneto-elastic surface waves in a conducting medium under an initial uniaxial tension has been deduced and then it has been employed to investigate the particular cases of surface waves such as Rayleigh, Love and Stoneley waves. Secondly, propagation of waves in an elastic layer has been considered using the fundamental equations of motion for magneto-elastic waves in conductors under an initial uniaxial tension or compression. This is followed by the case of plane Lamb's problem in a magneto-elastic semi-space under the same initial tension. The final results obtained in the above cases are in agreement with the corresponding classical problems when the initial tension is zero and the magnetic field is absent. 相似文献
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Summary The paper is concerned with the investigation of the magneto-elastic waves and disturbances in initially stressed conducting media. Firstly, (a) the steady state response to moving loads in a magneto-elastic initially stressed conducting medium under an uniaxial tension has been discussed. Secondly, (b) the Lamb's problem corresponding to a line load suddenly applied in a magneto-elastic initially stressed conducting half-space bounded by a plane under uniaxial tension has been investigated. The final results obtained in both cases are in agreement with the corresponding classical problems when the initial tension is zero and the magnetic field is absent. 相似文献
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Sukhendu Dey 《Pure and Applied Geophysics》1971,90(1):38-52
Summary In this paper, the frequency equation for phase velocity of waves propagated in a laminated medium consisting of two eleastic layers of finite thickness under initial stresses, has been obtained. It has been shown that when wave length becomes very small compared to the thickness of each layer, the wave approaches two Rayleigh waves at the two outer surfaces with the possibility of Stoneley waves at the interface. The propagation ofSH-waves in the composite medium under initial stresses has also been discussed. A particular case has been taken to find the velocity of Love wave in the homogeneous half space under initial compressive stresses.Biot's incremental deformation theory has been used. 相似文献
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D. K. Wagh 《Pure and Applied Geophysics》1972,99(1):49-54
Summary Cauchy theory of initial stress has been applied to investigate the problem of SH waves in an initialy stressed elastic plate. The initial stress is assumed to be a uniform tension or compression along the thickness of the plate. It is found that the initial stress influences the velocities of the dispersive modes only but, it has no influence on the velocity of the non-dispersive wave. 相似文献
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主要讨论了应力变化如何影响各向异性介质中波速度的问题。推导了一般各向异性介质在初始应力下的Christoffel方程,得到介质中3种波的相速度和初始应力的关系表达式;通过实验数据验证了单轴应力能够诱导各向异性,当施加单轴应力时,速度在沿应力的方向增加最大,在垂直应力的方向增加最小,实验结果与理论推导一致;用Christoffel方程的数值解模拟在3种对称情况下的弹性各向异性介质中初始应力对波速度的影响。数值结果表明:初始应力对各向异性介质中波传播速度的影响,随着各向异性强度的增加而增大,而且速度越慢,影响越大。 相似文献
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本文研究初始应力及磁场作用下导电粘弹体内的波动特性。首先导出有初始应力及磁场作用下导电粘弹体运动的基本方程,然后用它去研究流体静压力及单轴初始应力下波动方程的解,从平面简谐波的频散方程,分析了初始应力及磁场对波动传播的影响。粘弹体用Kelvin-Voigt模型,外磁场假定为均匀。所得结果表明,初始应力对波的影响随应力性质不同而有所差异,它既影响波的相速也影响波的衰减。磁场影响的大小决定于外磁场的强弱。从本文所得公式中,令外磁场为零,可得初始应力对波特性的影响;如令初始应力为零,就得到磁场对波的影响结果;令两者同时为零,即得粘弹波的经典结果。 相似文献
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针对鄂尔多斯盆地西缘黄土塬区复杂地表和复杂地下构造导致难以准确成像问题,采用浅层潜水波层析反演（DWT）速度建模技术,同时辅以中深层反射波层析成像技术,形成一套实用叠前深度偏移速度建模方法。首先生成一个基于钻井和解释信息的起始近地表速度,其次利用潜水波层析反演建立初始近地表模型,将其与常规处理获得的中深层速度模型进行匹配拼接,建立起初始的起伏地表全速度模型,然后在此基础上利用基于反射波的网格层析进行中深层速度建模,经过多轮次迭代,最终获得可靠的高精度速度模型。鄂尔多斯盆地西缘MJT工区地震资料的成像处理验证了这一套速度建模技术的有效性,地下构造成像更合理也更精确。 相似文献
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Analysing tension infiltrometer data from sloped surface using two‐dimensional approximation 
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下载免费PDF全文 Tension infiltrometers allow water to infiltrate into the soils at various specified pressure heads. The resulting infiltration rates can then be analysed for soil hydraulic properties by either analytical or inverse numerical methods. Tension infiltrometers however are primarily designed to be deployed on horizontal land surfaces, and their applications have been studied widely using an inverse numerical tool HYDRUS‐2D. However, natural landscapes are often nonhorizontal, and infiltration through tension infiltrometers on sloped surfaces is no longer an axisymmetrical two‐dimensional (2D) process but a fully three‐dimensional (3D) one. In addition, minimal research has examined the effect of simplifying the 3D problem to a 2D one on the hydraulic conductivity estimated using tension infiltrometer data from different land slopes of various soil types. Therefore, in this study, tension infiltrometer data on different slopes have been obtained from a catchment located at National University of Singapore. In addition, tension infiltrometer data of six soil types on different slopes and with different initial water content were simulated using HYDRUS‐3D. Combining field measurements, forward and inverse modelling, the influence of applying a 2D approximation on hydraulic property estimations using tension infiltrometer data was examined. The results show that the estimations for soils with high infiltration rates are more sensitive to application of the 2D approximation. The maximum allowable slopes for employing 2D approximation on clayey and sandy soils are 25° and less than 3°, respectively. Furthermore, the maximum allowable slope decreases with decreasing initial water content. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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45287 P-wave and 26813 S-wave arrival times from the data base of the Costa Rica network have been tomographically inverted to image the structure beneath Costa Rica. A regularized recursive least squares inverse method was used to produce the high resolution and minimum variance model parameter estimates. The first arrival times are calculated using a finite difference technique, which allows for flexible parameterization of the velocity model and easy inclusion of topography and source-receiver geometry. The P wave velocity structure and hypocenters are determined simultaneously, while the S wave velocity structure is determined using the relocated seismicity and an initial model derived from the P wave model assuming an average P to S wave velocity ratio of 1.78. The most prominent features in the inverted model are a low velocity structure under the volcanic chain in the center of the country, which is related to the hot material connected with the active volcanoes; and a high velocity zone in the mantle, which is related to the Cocos plate subducted under Costa Rica. 相似文献
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A case history is reported to outline a possible strategy for the construction of a pseudo-2D model of shear-wave velocity for seismic site response studies. Experimental data have been collected using the Multichannel Analysis of Surface Wave technique (MASW) at six sites in the city of Najaf (Southern Iraq). The sites are aligned along the route of a proposed subway. The dataset has been processed to extract the dispersion curves of each site and then it has been inverted by using a Laterally Constrained Inversion (LCI) algorithm. The initial model for the local search algorithm has been obtained with a preliminary Monte Carlo Inversion (MCI). A priori information from borehole logs and lateral constraints between neighbors 1D models are used to mitigate the non-uniqueness of the solution. The result is a pseudo-2D shear-wave velocity model of the area which is in good agreement with sediment lithology and thicknesses obtained from borehole logs. 相似文献
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运用ＣＴ技术中的傅利叶重建法，根据任意所给的两个初始速度模型，用几组平行射线束进行扫描，采集走时数据，并利用走时数据反演速度图象．反演结果与初始模型比较两者基本相符合。由此证明，傅利叶重建法在一定条件下可以用来反演地壳速度结构，并可得到较好的结果．这种方法是ＣＴ技术应用于地学研究的一种新的尝试． 相似文献
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本文通过对径向接收函数和垂直向接收函数进行低通滤波,获取了S波视速度随低通滤波参数的变化曲线,然后利用经验关系将它转换成了台站下方的S波速度结构,并以此作为接收函数反演的初始模型.理论数值实验表明:由于初始模型的S波速度值提供了有效的约束,即使Moho面深度并不准确,但反演迭代过程还是快速地向真解逼近.另外,通过给观测波形加入10%的噪声,在保持S波速度不变的情况下,分别对波速比进行5%的正负扰动(即泊松比分别扰动为0.23和0.27),反演结果仍然快速向真解收敛.对保山台记录的远震接收函数反演结果表明:用本文方法反演所得结果与测深结果较为一致.这充分说明只要S波速度值(而非泊松比)能够提供有效的约束,接收函数的反演过程对P波速度的选取并不敏感. 相似文献
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使用阻尼最小二乘法进行震源参数和地壳三维速度结构的走时联合反演．所用资料为Ｓ波和Ｐ波到时差,并用人工地震资料的二维解释结果作为三维速度模型的特定约束条件．为建立初始模型,又利用天然地震构成了准二维剖面．在走时反演基础上,利用遗传算法进行了几个地震事件的波形反演尝试,并对走时反演获得的地壳速度结构模型的局部进行了修正．以３４°～４２°Ｎ,９４°～１１２°Ｅ作为研究区域,在该区域中收集了１９８６年以来大量地震的Ｓ波和Ｐ波到时差资料,７条人工地震二维速度剖面资料和２个数字化地震台的几个地震的三分向记录资料．对这些资料进行了处理,最后得出了０～２５ｋｍ深度不同截面的速度分布,并对所得结果进行了分析． 相似文献
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Introduction Shanxi uplift area is bounded by Ordos block to the west, Taihang Mountain front fault zone to the east. On the north side, it is also adjoined with Yinshan fold belt and Hetao-Baotou fault depression basin accompanied with its southern active ruptures, as well as on the south side, connected to Weihe fault depression basin accompanied with large ruptures on the northern margin of Qinling fold belt. The interior of the Shanxi uplift area, with complicated tectonic structures, … 相似文献
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叠加速度分析技术是常规地震资料处理中的重要环节,也是经典的时间域速度建模方法.叠加速度分析技术主要包括速度谱计算和拾取两个步骤.至今为止,多数研究工作通过提高速度谱的分辨率以及抗噪声能力,获得高质量的速度谱从而有利于拾取.本文的目标是将叠加速度分析技术转为一个全自动化的处理流程.从参数估计的角度出发,将叠加速度估计转化为稀疏反演框架下的模型参数估计问题,并通过稀疏反演算法自动反演叠加速度,进而提高叠加速度建模的效率.为实现这一目标,首先给出了正问题的定义,即层状介质中CMP道集的预测模型,利用叠加速度、垂向双程走时(t_0)以及反射子波以及CMP道集时距关系(如双曲时距关系)可以预测CMP道集.接着,速度分析反问题可以描述为已知观测的CMP道集,估计模型参数(叠加速度及t_0时间等).利用模型参数的稀疏性作为约束条件并用L_0范数作为模型稀疏性的度量准则,叠加速度分析可以转化为L_0范数约束下的稀疏反演问题.本文提出了一种基于预测校正思想的匹配追踪算法求解上述反问题,实现了自动叠加速度建模并为后续的高精度速度反演方法提供较好的初始模型.理论和实际资料的测试结果证明了本文方法的有效性. 相似文献
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Summary The possibility of generation of magnetohydrodynamic waves in a rotating spherical system under the efect of small disturbances of the medium velocity is investigated. The initial stationary state of the system has been chosen with a view to known geophysical facts, and the effect of the solid inner core is considered. It is proved that two types of waves with distinctly different frequencies can be generated in the liquid region. The behaviour of longperiod magnetic waves is also studied in detail, and it is proved that the direction in which they propagate at a certain point depends on the position of this point in the meridional plane and on the configuration of the initial magnetic field. The phase velocities of the longperiod magnetic waves, propagating towards the west, have been computed within a selected network of points and the region in which they are generated has been defined. It is proved that the phase velocities of these waves are compatible with the observed velocity of the westward drift of the geomagnetic dipole. 相似文献
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Simulated raindrops falling in still air have a shape that is mainly determined by surface tension and hydrostatic pressure. Drops released from capillary tips show an initial shape variation ranging from prolate to oblate but eventually this oscillation is damped. At terminal velocity drops have attained equilibrium and have an oblate shape. Measurements of the shape of simulated rain drops produced by capillary tubes were made using a simple, newly-developed photographic set up. The measurements showed that models describing the oscillation frequency and amplitude of drops falling at terminal velocity can also be applied to the simulated drops. A comparison is made between the shape of raindrops in natural storms and simulated drops. Recommendations are given regarding fall heights in simulation in relation to the drop shape in nature. 相似文献
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Salvatore de Lorenzo Maddalena Michele Antonio Emolo Andrea Tallarico 《Journal of Seismology》2017,21(4):909-919
We investigate the elastic properties of the crust in the Gargano promontory, located in the northern part of the Apulia region (Southeastern Italy). Starting on April, 2013, a local-scale seismic network, composed of 12 short-period (1 Hz) seismic stations, was deployed on the Gargano promontory. Starting on October, 2013, the network was integrated with the recordings of nine seismic stations managed by the Italian Institute of Geophysics and Volcanology (INGV). The network recorded more than 1200 seismic events in about 15 months of data acquisition, with more than 700 small magnitude events localized in the Gargano promontory and surrounding areas. A Wadati-modified method allowed us to infer VP/VS = 1.73 for the area. A subset of about 400 events having a relatively smaller azimuthal gap (<200°) was selected to calibrate a 1D P-wave velocity model of the area, using the VELEST inversion code. The preferred model was obtained from the average of ten velocity models, each of them representing the inversion result from given initial velocity models, calibrated on previous geological and geophysical studies in the area. The results obtained under the assumption that VP could decrease with depth are unstable, with very different depths of the top of low-velocity layers. Therefore, the velocity model was obtained from the average of the results obtained under the assumption that VP cannot decrease with depth. A strong reduction of both RMS (about 58%) and errors on the location of the events was obtained with respect to the starting model. The final velocity model shows a strong velocity gradient in the upper 5 km of the crust and a small increase (from 6.7 to 7 km) at 30 km of depth. The epicenters of relocated events do not show clear correlations with the surface projection of known seismic faults. A cluster of the epicenters of the relocated events intersects almost perpendicularly the Candelaro fault trace at the surface. 相似文献