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该文通过对CRUST2.0+PREM 16200个区域一维地球模型简正模频率的计算,得到简正模非线性地壳改正效应.结果表明:地壳改正的非线性化改正不可或缺,对于低频简正模,其影响较小;对于高频简正模,其影响较大,这一变化遵循能量密度函数分布规律.此外,该文将CRUST2.0网格数据展开成球谐函数,并在此基础上计算了地壳侧向非均匀导致的二阶谱峰分裂系数.将其与地幔对应系数比较得出:前者造成的简正模谱峰分裂通常远远小于后者;地壳造成的二阶谱峰分裂主要贡献来自于间断面地形起伏(地壳厚度等)而非地壳的侧向非均匀参数扰动;在反演地幔结构时必须扣除地壳对简正模谱峰分裂系数的影响. 相似文献
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Study of azimuthal anisotropy in the transition zone of the Earth's upper mantle with the coupling of normal modes 
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下载免费PDF全文 地震方位各向异性广泛存在于地球上地幔中,目前利用地震体波或面波分析研究上地幔各向异性的地球物理方法有很多种,但是由于各自的局限性均难以分析上地幔过渡区中的各向异性特征.方位各向异性可导致球形简正模和环形简正模之间发生耦合.地球长周期自由振荡的简正模可深入到上地幔过渡区.本文利用各向异性地球模型计算各向异性简正模耦合深度敏感核,表明长周期(250～400 s)简正模各向异性耦合(如0S20-0T21和0S25-0T25)的敏感度峰值在400～600 km之间.在不受地球自转影响的台站,如位于南极极点的QSPA站,仍然可以观测到强烈的简正模耦合现象.本文的研究表明:只有在地震观测台站靠近长周期球形振荡的节点时,才能在其观测数据中观测到各向异性耦合现象,许多各向异性耦台在震后18～24 h期间最强,并可导致垂直方向的环形简正模的振幅大于球形耦合简正模的振幅.这些特征是在地震观测数据中寻找各向异性耦合的重要线索.长周期简正模的方位各向异性耦合为我们提供了一个新的认识上地幔过渡区各向异性的窗口. 相似文献
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地震方位各向异性广泛存在于地球上地幔中,目前利用地震体波或面波分析研究上地幔各向异性的地球物理方法有很多种,但是由于各自的局限性均难以分析上地幔过渡区中的各向异性特征.方位各向异性可导致球形简正模和环形简正模之间发生耦合.地球长周期自由振荡的简正模可深入到上地幔过渡区.本文利用各向异性地球模型计算各向异性简正模耦合深度敏感核,表明长周期(250~400 s)简正模各向异性耦合(如0S20-0T21 和0S25-0T25)的敏感度峰值在400~600 km之间.在不受地球自转影响的台站,如位于南极极点的QSPA站,仍然可以观测到强烈的简正模耦合现象.本文的研究表明:只有在地震观测台站靠近长周期球形振荡的节点时,才能在其观测数据中观测到各向异性耦合现象,许多各向异性耦合在震后18~24 h期间最强,并可导致垂直方向的环形简正模的振幅大于球形耦合简正模的振幅.这些特征是在地震观测数据中寻找各向异性耦合的重要线索.长周期简正模的方位各向异性耦合为我们提供了一个新的认识上地幔过渡区各向异性的窗口. 相似文献
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在构建现代地球模型时,地球内部分层结构主要是根据地震波资料确定的;而地球内部密度及弹性参数,特别是地幔以下大尺度结构的密度分布,则主要是根据地球自由振荡的弹性简正模观测资料确定的.本文概述了地球自由振荡简正模本征值的求解理论和方法,介绍了球型和环型模态位移场表达式,讨论了地球自由振荡模态的衰减、分裂与耦合效应;总结了多线态分裂谱线探测和分裂参数估计的方法,综述了利用弹性简正模开展地震矩张量、地球三维非均匀性结构和内核超速旋转约束与反演研究的主要进展和存在的问题.最后作为展望,本文还讨论了地球自由振荡简正模的未来研究趋势. 相似文献
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大地震激发导致的地球自由振荡可为获得地球深部结构提供重要手段,通过理论计算自由振荡简正模的本征周期,并与实测结果进行比较,可为地球深内部结构和新地球模型的研究提供有效约束.采用微分方程数值积分技术和G-D1066A地球模型,本文计算了0~48阶的187个球型自由振荡简正模的本征周期,将计算结果与Gilbertt和Dziewonski等3组模型理论结果及Ness等4组观测结果进行比较,相对偏差在0.3%以内.分析说明由于考虑了地幔、外核和内核等不同分层密度和拉梅参数变化的影响,获得了较高精度的地球自由振荡简正模周期.本文提供的理论计算结果可为修正真实地球内部参数提供有效参考. 相似文献
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地震会改变地球的形状,引起内部物质的重新分布,从而导致地球的惯性张量产生变化.依据角动量守恒定律,地球的自转将会发生变化.为了探究大地震对地球自转的影响,本文基于简正模和点源位错两种不同的理论,应用PREM地球模型,以2000年至今的10个8.3级以上的大地震为例,分别计算了地震发生后地球重力场的斯托克斯系数、地球的总惯性张量、地球扁率等的变化.讨论了简正模方法叠加的收敛性问题,并对震级的影响进行了简单的分析,着重探究了深度变化对地球极移和日长变化的影响.结果表明:在相同的地球模型下,利用简正模和位错两种理论计算的日长和极移的结果是一致的;简正模方法的收敛速度比较快,只需叠加3个左右的低频简正模就已经收敛;对于震级大于4.5级的地震,极移激发的方向出现在120°E~160°E的概率大一些;通常情况下,越深源的和震级较大的地震,极移激发的幅度和日长变化量越大.此外,在0~700 km深度区间内,随着深度的增加,极移激发的幅度和日长变化总体表现为增加的趋势. 相似文献
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在计算面波频散问题的广义反射-透射系数方法基础上研究了含有低速层的均匀平层固体地球模型的面波的频散曲线以及简正振型的计算问题. 当不存在低速层时,仅利用陈晓非1993年提出的单一的久期函数对求解这两个问题已经足够. 但是当模型中存在低速层时,该单一久期函数在数值求解较低阶模式很困难. 本文提出用久期函数族代替该单一久期函数、对不同的简正振型模式采用对应的久期函数来求解的方法,从而更加容易有效地求解较低阶的模式,完善了利用广义反射-透射系数方法求解面波频散问题的理论和算法. 相似文献
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实际地震勘探中,储层物性参数的差异是导致地震波响应特征发生变化的根本原因,而建立储层物性参数与地震响应特征之间的联系,需要跨越微观孔隙尺度、介观测井尺度以及宏观地震尺度等三个不同尺度空间.本文基于已知井的岩石物理实验数据和测井数据,利用复杂多孔隙介质理论将微观尺度孔隙岩石粗化到介观测井尺度,利用Backus平均理论将介观测井尺度的模型进一步粗化到宏观地震尺度,最终,得到地震尺度裂缝-多孔隙介质模型.其数值计算结果与测井数据和地震数据的对比表明：基于两级尺度粗化算法的裂缝多孔隙介质模型在给定参数下是有效的,且基于该模型的地震响应特征分析方法能够对储层的地震响应特征随物性参数的变化进行分析. 相似文献
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本文拓展了一种模拟地震波在地球核幔边界D″区各向异性介质中传播的数值方法:谱元-简正振型耦合方法(CSEM).该方法通过在球对称各向同性介质空间采用简正振型方法,在各向异性的D″区采用谱元方法,并在两种介质的边界采用"DtN"算子耦合的策略计算一维模型PREM(见文献[1])或修改后的D″区横向各向同性VTI-PREM模型的理论地震图.模拟所得数值解结果与采用简正振型方法得到的解析解结果进行对比以验证方法的精度.在中国科学院地球深部结构重点实验室高性能计算机上使用128个CPU计算得到的结果显示,在10-5～0.125 Hz的频率范围内谱元简正振型法得到的波形与简正振型方法能很好拟合.此外,对于VTI介质结构模型,谱元简正振型法能够准确模拟S波分裂现象,从而验证了谱元简正振型耦合方法对各向异性介质中地震波传播数值模拟是一种有效的方法. 相似文献
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We study the interaction of a seismic wavefield with a spherical acoustic gas‐ or fluid‐filled cavity. The intention of this study is to clarify whether seismic resonances can be expected, a characteristic feature that may help in detecting cavities in the subsurface. This is important for many applications, in particular the detection of underground nuclear explosions, which are to be prohibited by the Comprehensive Test Ban Treaty. To calculate the full seismic wavefield from an incident plane wave that interacts with the cavity, we considered an analytic formulation of the problem. The wavefield interaction consists of elastic scattering and the wavefield interaction between the acoustic and elastic media. Acoustic resonant modes caused by internal reflections in the acoustic cavity show up as spectral peaks in the frequency domain. The resonant peaks coincide with the eigenfrequencies of the un‐damped system described by the particular acoustic medium bounded in a sphere with stiff walls. The filling of the cavity could thus be determined by the observation of spectral peaks from acoustic resonances. By energy transmission from the internal oscillations back into the elastic domain, the oscillations experience damping, resulting in a frequency shift and a limitation of the resonance amplitudes. In case of a gas‐filled cavity, the impedance contrast is still high, which means low damping of the internal oscillations resulting in very narrow resonances of high amplitude. In synthetic seismograms calculated in the surrounding elastic domain, the acoustic resonances of gas‐filled cavities show up as persisting oscillations. However, due to the weak acoustic–elastic coupling in this case, the amplitudes of the oscillations are very low. Due to a lower impedance contrast, a fluid‐filled cavity has a stronger acoustic–elastic coupling, which results in wide spectral peaks of lower amplitudes. In the synthetic seismograms derived in the surrounding medium of fluid‐filled cavities, acoustic resonances show up as strong but fast decaying reverberations. 相似文献
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Manuel Ortega-rodríguez Alexander S. Silbergleit Robert V. Wagoner 《地球物理与天体物理流体动力学》2013,107(1):75-115
This article studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing Wentzel-Kramers-Brillouin (WKB) techniques, we obtain the eigenfrequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and show for the first time that modes covering the whole extension of the disk (full-disk p-modes) can exist within the studied thin disk model. However, these modes have relatively short wavelengths. 相似文献
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裂缝诱导的双相具有水平对称轴的横向各向同性(HTI)介质模型是由一组平行排列的垂直裂缝嵌入到统计各向同性的流体饱和多孔隙岩石中而组成的,它综合考虑了裂缝型储层岩石的各向异性和孔隙性.高精度的地震波场数值模拟技术是研究该介质中地震波传播规律的主要方法.本文结合错格伪谱法和时间分裂法,求解描述该介质中地震波传播的一阶速度-应力方程.模拟了单层和双层模型中的地震波场,并对其进行了特征分析.研究结果表明:错格伪谱法能有效消除标准网格伪谱法波场模拟结果中出现的数值伪影现象,与时间分裂法结合能够获得稳定的、高精度的模拟结果;裂缝诱导双相HTI介质中的地震波场兼具裂缝各向异性介质和双相介质中传播的地震波的波场特征. 相似文献
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Yanadet Sripanich Sergey Fomel Junzhe Sun Jiubing Cheng 《Geophysical Prospecting》2017,65(5):1231-1245
The goal of wave‐mode separation and wave‐vector decomposition is to separate a full elastic wavefield into three wavefields with each corresponding to a different wave mode. This allows elastic reverse‐time migration to handle each wave mode independently. Several of the previously proposed methods to accomplish this task require the knowledge of the polarisation vectors of all three wave modes in a given anisotropic medium. We propose a wave‐vector decomposition method where the wavefield is decomposed in the wavenumber domain via the analytical decomposition operator with improved computational efficiency using low‐rank approximations. The method is applicable for general heterogeneous anisotropic media. To apply the proposed method in low‐symmetry anisotropic media such as orthorhombic, monoclinic, and triclinic, we define the two S modes by sorting them based on their phase velocities (S1 and S2), which are defined everywhere except at the singularities. The singularities can be located using an analytical condition derived from the exact phase‐velocity expressions for S waves. This condition defines a weight function, which can be applied to attenuate the planar artefacts caused by the local discontinuity of polarisation vectors at the singularities. The amplitude information lost because of weighting can be recovered using the technique of local signal–noise orthogonalisation. Numerical examples show that the proposed approach provides an effective decomposition method for all wave modes in heterogeneous, strongly anisotropic media. 相似文献
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The wavefield transform is a mathematical technique for transforming low-frequency electromagnetic (EM) signals to a non-diffusive wave domain. The ray approximation is valid in the transform space and this makes traveltime tomography for 3D mapping of the electrical conductivity distribution in the subsurface possible. The transform, however, imposes stringent frequency bandwidth and signal-to-noise ratio requirements on the data. Here we discuss a laboratory scale experiment designed to collect transform quality EM data, and to demonstrate the practical feasibility of transforming these data to the wavefield domain.
We have used the scalable nature of EM fields to design a time-domain experiment using graphite blocks to simulate realistic field conditions while leaving the time scale undisturbed. The spatial dimensions have been scaled down by a factor of a thousand by scaling conductivity up by a factor of a million. The graphite blocks have two holes drilled into them to carry out cross-well and borehole-to-surface experiments. Steel sheets have been inserted between the blocks to simulate a conductive layer.
Our experiments show that accurate EM data can be recorded on a laboratory scale model even when the scaling of some features, such as drill-hole diameters, is not maintained. More importantly, the time-domain EM data recorded in cross-well and surface-to-borehole modes can be usefully and accurately transformed to the wavefield domain. The observed wavefield propagation delay is proportional to the direct distance between the transmitter and receiver in a homogeneous medium. In a layered medium, data accuracy is reduced and, hence, our results are not so conclusive. On the basis of the experimental results we conclude that the wavefield transform could constitute a valid approach to the interpretation of accurate, undistorted time-domain data if further improvement in the transform can be realized. 相似文献
We have used the scalable nature of EM fields to design a time-domain experiment using graphite blocks to simulate realistic field conditions while leaving the time scale undisturbed. The spatial dimensions have been scaled down by a factor of a thousand by scaling conductivity up by a factor of a million. The graphite blocks have two holes drilled into them to carry out cross-well and borehole-to-surface experiments. Steel sheets have been inserted between the blocks to simulate a conductive layer.
Our experiments show that accurate EM data can be recorded on a laboratory scale model even when the scaling of some features, such as drill-hole diameters, is not maintained. More importantly, the time-domain EM data recorded in cross-well and surface-to-borehole modes can be usefully and accurately transformed to the wavefield domain. The observed wavefield propagation delay is proportional to the direct distance between the transmitter and receiver in a homogeneous medium. In a layered medium, data accuracy is reduced and, hence, our results are not so conclusive. On the basis of the experimental results we conclude that the wavefield transform could constitute a valid approach to the interpretation of accurate, undistorted time-domain data if further improvement in the transform can be realized. 相似文献
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Up–down wavefield decomposition is effectuated by a scaled addition or subtraction of the pressure and vertical particle velocity, generally on horizontal or vertical surfaces, and works well for data given on such surfaces. The method, however, is not applicable to decomposing a wavefield when it is given at one instance in time, i.e. on snapshots. Such situations occur when a wavefield is modelled with methods like finite-difference techniques, for the purpose of, for example, reverse time migration, where the entire wavefield is determined per time instance. We present an alternative decomposition method that is exact when working on snapshots of an acoustic wavefield in a homogeneous medium, but can easily be approximated to heterogeneous media, and allows the wavefield to be decomposed in arbitrary directions. Such a directional snapshot wavefield decomposition is achieved by recasting the acoustic system in terms of the time derivative of the pressure and the vertical particle velocity, as opposed to the vertical derivative in up–down decomposition for data given on a horizontal surface. As in up–down decomposition of data given at a horizontal surface, the system can be eigenvalue decomposed and the inverse of the eigenvector matrix decomposes the wavefield snapshot into fields of opposite directions, including up–down decomposition. As the vertical particle velocity can be rotated at will, this allows for decomposition of the wavefield into any spatial direction; even spatially varying directions are possible. We show the power and effectiveness of the method by synthetic examples and models of increasing complexity. 相似文献
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改进BISQ(Biot-Squirt)机制在不引入特征喷流长度的情况下,将含流体孔隙介质中Biot流动和喷射流动两种重要的力学机制有机地结合起来,且各相关参数具有明确物理意义和可实现性.本文将改进BISQ机制一维孔隙流体压力公式推广到三维具有水平对称轴横向各向同性介质(HTI介质)情况,结合裂缝各向异性理论,给出了基于改进BISQ机制的双相HTI介质模型及其二维三分量波传播方程,采用伪谱法求解该方程,进行了不同相界、不同频率以及双层地质结构情况下该类介质中波场的数值模拟与特征分析.数值模拟结果表明:伪谱法模拟精度高,压制网格频散效果好,可以得到高精度的波场快照和合成记录;基于改进BISQ机制的双相HTI介质模型兼具裂缝各向异性特征和孔隙弹性特征,其为从双相各向异性理论角度深入研究裂缝性储层的地震响应奠定了理论基础. 相似文献
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Nonhydrostatic Atmospheric Normal Modes on Beta-Planes 总被引：1，自引：0，他引：1
--To facilitate the understanding of nonhydrostatic effect in global and regional nonhydrostatic models, the normal modes of a nonhydrostatic, stratified, and compressible atmosphere are studied using Cartesian coordinates on midlatitude and equatorial #-planes. The dynamical equations without forcing and dissipation are linearized around the basic state at rest, and solved by using the method of separation of variables. An eigenvalue-eigenfunction problem is formulated, consisting of the horizontal and vertical structure equations with suitable boundary conditions. The wave frequency and the separation parameter, referred to as "equivalent height," appear in both the horizontal and vertical characteristic equations as a coupled problem, unlike the hydrostatic case. Therefore, the nonhydrostatic equivalent height depends not only on the vertical modal scale, as in the hydrostatic case, but also on the zonal and meridional modal scales. Numerical resu lts on the dispersion relations are presented for an isothermal atmosphere. Three kinds of normal modes, namely acoustic, gravity, and Rossby modes, are solved and compared with the corresponding global solutions. Nonhydrostatic effects are studied in terms of normal modes in a wide range of wavelengths from small to planetary scales. It is demonstrated that Rossby modes are hardly affected by nonhydrostatic effects regardless of wavelengths. However, nonhydrostatic effects on gravity modes become significant for smaller horizontal and deeper vertical scales of motion. The equivalent height plays a particularly important role in evaluating nonhydrostatic effects of normal modes on the equatorial #-plane, because the equivalent height appears in the scaling of meridional distance variable of the eigenfunctions. The implementation of nonhydrostatic normal mode analysis on high-resolution numerical modeling is also discussed. 相似文献