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传统的人工边界是在声波或弹性波分解为内行和外行分量的基础上设计的.对于较复杂的介质模型（如粘弹介质、弹塑介质、塑性介质模型等）,地震波不能简单地分解为各自满足其运动方程的纵波、横波等成分,且地震波在传播过程中还有衰减现象,因此传统的人工边界已不能有效地用于非弹性的较复杂介质的波场模拟.本文提出了一种适合于更一般的地震模型的波场计算的透射边界条件,并以粘弹介质的一个较简单的二维几何模型为例,通过有限元数值求解这种透射边界和刚性边界下粘弹波的激发和传播,得到地面合成地震记录,证明了这种透射边界用于较复杂介质波场计算是可行的. 相似文献
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地震波散射:理论与应用 总被引：4，自引：0，他引：4
传统的球面对称(或层状构造)地球模型正经历着一场革命。地球被揭示从地壳、地幔到地核到处都呈现多尺度的横向非均匀性。这些具有不同尺度的非均匀体对地震波具有不同的效应。速度和密度的非均匀体能改变波形,引起走时和振幅的起伏以及产生直达波的视衰减。地球岩石层的非均匀体还能产生P尾波、S尾波和Lg尾波等。核-幔边界附近的非均匀体能产生对PKP波的散射而成为PKIKP的前驱波,PKKP波的散射波可成为主震相自己的前驱波。近源和近台站的复杂构造可通过共振、散射来改变地震波形。粗糙地形或粗糙界面能造成体波和面波的耦合。地壳内规则排列的裂隙可产生有效各向异性而使S波分裂。由三维非均匀体所引起的地震波的变化,在广义上被称为地震波散射。近十多年来,由于高质量的高频数字地震资料的逐渐增多,对地震波散射的研究在急速发展并引起了越来越多的地震学家、工程学家和勘探地球物理学家的兴趣。本文综述了地震波散射的基本理论和在这一领域各方面的最新进展。其内容大致为:一、地球横向非均匀性的谱及各种散射态式二、地震波散射的研究方法1.理论研究(1)不连续非均匀介质的边界匹配方法(2)弱散射的微扰法(3)高频近似法(4)随机方法和非均匀体的统计特性2.数值模拟和物理模型试验3.野外观测三、弹性波散射的基本特征和标量波近似1.弹性波瑞雷散射2.弹性波瑞雷-甘斯散射3.随机介质的弹性波散射四.地震波散射的表现和应用1.透射起伏2.尾波产生及包络消减3.散射衰减4.核-幔边界附近的散射5.地表地形、近地表结构和深部构造引起的散射6.裂缝散射和有效各向异性7.散射和非线性。 相似文献
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随机弹性介质中地震波散射衰减分析(英文) 总被引：2，自引：0，他引：2
地震波衰减一直是许多学科研究的热点,因为可以反映介质的特性。导致地震波衰减的因素很多,如:传播过程中由于能量扩散导致的几何衰减,固体岩石内部晶粒间相对滑移导致的摩擦衰减,岩石结构不均匀引起的地震波散射衰减。本文主要从统计的观点出发,通过多次数值模拟的方法研究纵波散射在随机弹性介质中所引发的衰减。首先用随机理论建立了二维空间随机弹性介质模型,然后用错格伪谱法的数值方法模拟了波在随机介质中的传播,再通过波场中虚拟检波器的记录,用谱比法估计了弹性波在随机介质中的散射衰减。不同非均匀程度随机弹性介质中的数值结果表明:介质不均匀程度越高,散射衰减越大;在散射体尺寸小于波长的前提下,不同散射体尺寸的计算结果说明:散射体尺寸越大,弹性波衰减越明显。最后提出了一种不均匀孔隙介质中流体流动衰减的方法。通过对随机孔隙介质中地震波的总衰减和散射衰减分别进行了计算,并定量得出了随机孔隙介质中流体流动衰减,结果表明:在实际地震频段下,当介质不均匀尺度101米量级时,散射衰减比流体流动衰减要大,散射衰减是地震波在实际不均匀岩石孔隙介质中衰减的主要原因。 相似文献
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双相介质地震波场数值模拟的迭积微分算子及其PML边界条件 总被引：1，自引：1，他引：0
将基于计算数学中Forsyte 广义正交多项式的迭积微分算子引入到地震波动方程的一阶速度--应力方程的空间微分运算中去,并采用时间错格有限差分算子替代传统的差分算子以匹配高精度的空间迭积微分算子,从而发展一种全新的地震波场正演模拟方法,来解决复杂非均匀介质模型中的波场传播问题.为了大幅衰减人工边界引起的反射,本文将完全匹配层(Perfectly Matched Layer,PML)吸收边界条件引入到所构建的方法中,以解决迭积微分算子法的边界问题.以二维波动方程为例,用迭积微分算子法实现了双相介质的地震波场正演模拟,模拟结果表明,双相介质模型较好地解释了含流体孔隙特性.同时也表明迭积微分算子法是一种非常实用、有效的数值模拟方法. 相似文献
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超高频（几百兆赫兹）超声数值模拟微米至纳米尺度的龙马溪组页岩数字岩芯及其强非均质性严重挑战数值模拟算法的精度和数值稳定性.本文利用图像阈值分割算法将龙马溪组页岩数字岩芯主要成分分解为石英类、黏土类、黄铁矿及孔隙四种类型,假定液相（油）均匀分布在整个介质模型中,根据岩芯的孔隙度、渗透率和各类矿物的岩石物理参数,建立了精细的非均质双相介质模型.采用基于Biot双相介质方程的不分裂卷积完全匹配层与高精度旋转交错网格有限差分方法精确模拟超声波在页岩岩芯中传播的散射衰减.通过精确控制匹配层吸收边界数来模拟边界反射量及其对尾波的干涉强度,并与超声实验尾波散射Q值进行比较,估算超声实验中的边界反射量及其对尾波的干涉强度.对不同超声子波主频的数值模拟试验,结合L/a-ka散射态式图分析表明：本文采用的龙马溪组页岩数字岩芯的非均质强度与600 MHz波长尺度相当,产生的散射衰减达到最大.开展页岩岩芯超声波散射数值模拟研究,据此评估页岩岩芯的非均质性,为页岩储层声学非均质预测提供依据. 相似文献
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地震波场数值模拟是理论地球物理学和勘探地球物理学的重要研究手段.在众多数值模拟方法中边界元法和有限差分法是两种典型的地震波传播模拟计算方法.边界元法是一种半解析-半数值的边界型方法,它显式地利用边界连续条件,沿着地层边界进行离散,具有降维、高精度和自动满足远场辐射条件的优点;有限差分法是一种典型的基于微分的区域型方法,它隐式地使用边界连续条件,以空间网格形式进行离散和数值逼近,具有高效、实用和容易数值实现的优点.本文以一个半圆形均匀Valley模型和两个非均匀断裂/断层模型为例,从计算精度、计算效率、频散特性以及适用性等方面对这两种方法进行了比较研究.数值计算结果表明:边界元法可以精确地几何描述有内部断点、断面的复杂构造,能够精确地模拟内部不规则界面之间波的反射/传播;有限差分法不能以足够的精度描述几何断点和内部不规则边界.边界元法在高频时计算量大于有限差分法,有限差分法则需要更小的网格间距以压制数值频散.因此,在处理内部非均质和高频计算时,有限差分法更有效;在处理内部不规则边界、断点、大尺度等问题时,边界元法比有限差分法更有优势. 相似文献
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《中国科学:地球科学》2016,(1)
地下岩石普遍存在着非均匀性,当井孔周围岩石的非均匀体的尺度(如压裂产生的裂缝系统)与声波波长相当时,会产生很强的散射波,因此可以通过声波测井的散射效应评价地层的非均匀性.文章基于弹性介质散射体在统计意义上的分布规律,建立了三维井孔非均匀介质模型,数值模拟了非均匀地层偶极声波测井的散射效应,并分析了散射波的衰减特性.模拟结果表明:与均匀介质相比,井孔周围非均匀体产生了明显的散射,一个显著的特征是在直达波之后出现了较强的尾波,且尾波的频率随着时间逐渐降低.在此基础之上,根据尾波的衰减特性提出了一种利用散射效应评价地层非均匀性的方法,并将该方法应用于致密储层的压裂效果评价.应用结果表明压裂后偶极声波测井散射效应产生的尾波预示着井孔周围岩石的体积改造,可以用来评价致密储层压裂效果,这为今后利用声波测井资料评价非常规储层(如页岩储层)的压裂效果提供了一条新的思路. 相似文献
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吸收衰减是地震波在实际地球介质中传播的固有特征.在实际应用中,通常假设表征吸收衰减特征的品质因子Q在地震频带范围内不随频率变化.高阶广义流变模型能够在时间域内精确的表征品质因子Q不随频率变化的特征,为黏弹性介质波动方程精细模拟奠定了基础.基于广义标准线性体模型理论,采用最小二乘拟合方法对Q值不随频率变化特征进行拟合,分析了不同阶次广义标准线性体模型对黏弹性介质Q值特征的拟合程度,在权衡计算精度和三维计算量的基础上,确定了五阶广义标准线性体模型并建立了相应的三维黏弹性波的速度-应力方程,结合CFS-PML边界条件开展了高精度三维黏弹性波正演模拟.通过均匀介质正演模拟,验证算法的正确性,明确了地震波的传播时的吸收衰减特征,对三维盐丘模型进行数值模拟,表明了五阶广义标准线性体可以精确的模拟黏弹性介质地震波吸收衰减特征. 相似文献
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矩形网格有限差分法在地震波传播数值模拟方面具有计算速度快的显著优势,但该方法在处理复杂边界问题上存在着效率低的严重缺陷.本文针对分段光滑曲线边界定义了尖点处的一种正则导数,给出了矩形网格情形分段光滑曲线网格边界点法向导数的一种插值计算方法.采用矩形网格有限差分法对复杂边界地球介质模型进行地震波场数值模拟,并采用波场系列快照技术揭示地震波在起伏地表和复杂介质中的传播规律.模拟结果表明：法向导数插值计算方法为矩形网格有限差分法处理复杂边界提供了有效途径,采用波场系列快照技术可以清晰地展现地震波在反射界面的反射和透射规律、在尖点的绕射规律以及在自由表面的直达波和多次反射规律. 相似文献
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Seismic Wave Propagation and Excitation in Multi-layered Media with Irregular Interfaces Part (Ⅰ): SH Case 总被引：1，自引：0，他引：1
Study of seismic wave excitation and propagation in laterally heterogeneous media was an active and important subject in seismology in the past two decades, numerous analytical and numerical efforts have been made in this research field. In this article, I have, first, made a brief review on those developments and then introduced and summarized a unified and efficient method, global generalized reflection-transmission (abbreviated to R/T thereafter) matrices method, for synthetic seismograms in multi-layered media with irregular interfaces developed by the author [24~26]. As demonstrated in this article, this method could be regarded as an extension of the generalized R/T coefficients method for the horizontally layered case [2,5] to the layered media with irregularly shaped interfaces by incorporating the T matrices technique [27,28]. Because of the use of a recursive scheme in computing the global generalized R/T matrices, this method is efficient, particularly for the case with a large number of irre 相似文献
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THE APPLICATION OF PML BOUNDARY CODITIONS IN THE SIMULATION OF SEISMIC WAVE BY THE HIGH-ORDER STAGGERED-GRID FINITE DIFFERENCES AT THE TRANSVERSELY ISOTROPIC MEDIA 
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下载免费PDF全文 In the realm of the numerical simulation, finite difference method and finite element method are more intuitive and effective than other simulation methods. In the process of simulating seismic wave propagation, the finite differences method is widely used because of its high computational efficiency and the advantage of the algorithm is more efficient. With the demand of precision, more and more researchers have proposed more effective methods of finite differences, such as the high-order staggered-grid finite differences method, which can restore the actual process of wave propagation on the premise of ensuring accuracy and improving the efficiency of operation. In the past numerical simulation of seismic wave field, different models of isotropic medium are mostly used, but it is difficult to reflect the true layer situation. With the research demand of natural seismology and seismic exploration, the research on anisotropic media is more and more extensive. Transversely isotropic(TI)media can well simulate the seismic wave propagation in the formation medium, such as gas-bearing sandstone, mudstone, shale et al., the character of TI media is reflected by introducing the Thomsen parameters to reflect its weak anisotropy of vertical direction by using Thomson parameter. Therefore, studying the process of seismic wave propagation in TI media can restore the true information of the formation to the greatest extent, and provide a more reliable simulation basis for the numerical simulation of seismic wave propagation. In the geodynamic simulation and the numerical simulation of the seismic wave field, under the limited influence of the calculation area, if no boundary conditions are added, a strong artificial boundary reflection will be generated, which greatly reduces the validity of the simulation. In order to minimize the influence of model boundaries on the reflection of seismic waves, it is often necessary to introduce absorbing boundary conditions. At present, there are three types of absorption boundary conditions: one-way wave absorption boundary, attenuation absorption boundary, and perfectly matched layer(PML)absorption boundary. In terms of numerical simulation of seismic waves, the boundary absorption effect of PML is stronger than the first two, which is currently the most commonly used method, and it also represents the cutting-edge development direction of absorption boundary technology. The perfectly matched layer absorbing boundary is effectively applied to eliminating the reflective waves from model boundaries, but for transversely isotropic medium, the effect of the absorbing is not very well. For this reason, the elastic dynamic wave equations in transversely isotropic media are derived, and we describe a second-order accurate time, tenth-order accurate space, formulation of the Madariaga-Virieux staggered-grid finite difference methods with the perfectly matched layer(PML)are given. In addition, we have established vertical transversely isotropic(VTI)media and arbitrary inclined tilted transversely isotropic(TTI)media models, using a uniform half-space velocity model and a two-layer velocity model, respectively. By combining the actual geoscience background, we set the corresponding parameters and simulation conditions in order to make our model more research-oriented. When setting model parameters, different PML thickness, incident angle, source frequency and velocity layer models were transformed to verify the inhibition of boundary reflection effect by PML absorption boundary layer. The implementations of this simulation show that the formula is correct and for the transversely isotropic(TI)media of any angular symmetry axis, when the thickness of the PML layer reaches a certain value, the seismic wave reflection effect generated by the artificial boundary can be well suppressed, and the absorption effect of PML is not subject to changes in incident angle and wave frequency. Therefore, the results of our study indicate that our research method can be used to simulate the propagation process of seismic waves in the transversely isotropic(TI)media without being affected by the reflected waves at the model boundary to restore the actual formation information and more valuable geological research. 相似文献
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近年来构造高精度、高效且具有长时程跟踪能力的保结构算法已逐渐成为地震波模拟算法发展的重要方向之一. 本文基于谱元法(SEM)进行空间域离散结合新推导的三阶辛算法(NTSTO)进行时间域离散,构造了一种具有时-空保结构特性的新算法. 本文给出的多组数值试验对比结果表明,本算法无论在内存消耗、稳定性及计算耗时,还是长时程跟踪能力方面都有上佳的表现; 另外,本文给出的起伏地表多层介质模型的数值算例验证了该算法处理复杂几何形状和复杂介质时的有效性. 该多辛结构谱元法的发展将为长时程地震波传播的计算及模拟提供更为广泛而有效的选择. 相似文献
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应用混合变量弹性动力学方程和线性常微分方程组的矩阵指数解法，将层状介质中广泛应用的弹性波传播矩阵解法推广至横向非均匀介质，给出了一种可计算复杂地质体中弹性波传播的广义传播矩阵数值解法。该方法可模拟任意震源及所产生的各种体波、面波，数值结果表明具有很高的计算精度。 相似文献
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孔隙介质弹性波传播理论在地球物理勘探、地震工程和岩土动力学等领域有着广泛的应用.而孔隙介质中的弹性波受孔隙度、渗透率、流体黏滞系数等参数的影响,因此研究波场的传播特征将有助于分析和提取这些信息.本文在Biot理论的基础上,针对三维层状孔隙介质模型,利用在合成理论地震图的研究中已经被证实具有稳定、高效且适用范围较广的Luco-Apsel-Chen（LAC）广义反透射方法,给出了弹性波场的一种积分形式的半解析解,可通过数值方法高效、准确地计算层状孔隙介质中的理论波场,所以该积分形式的半解析解可为三维层状孔隙介质波场传播特征的理论数值模拟研究提供一种新的途径和手段. 相似文献
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Seismic wavefield modeling in media with fluid-filled fractures and surface topography 总被引：3，自引：0，他引：3
We present a finite difference (FD) method for the simulation of seismic wave fields in fractured medium with an irregular (non-flat) free surface which is beneficial for interpreting exploration data acquired in mountainous regions. Fractures are introduced through the Coates-Schoenberg approach into the FD scheme which leads to local anisotropic properties of the media where fractures are embedded. To implement surface topography, we take advantage of the boundary-conforming grid and map a rectangular grid onto a curved one. We use a stable and explicit second-order accurate finite difference scheme to discretize the elastic wave equations (in a curvilinear coordinate system) in a 2D heterogeneous transversely isotropic medium with a horizontal axis of symmetry (HTI). Efficiency tests performed by different numerical experiments clearly illustrate the influence of an irregular free surface on seismic wave propagation in fractured media which may be significant to mountain seismic exploration. The tests also illustrate that the scattered waves induced by the tips of the fracture are re-scattered by the features of the free surface topography. The scattered waves provoked by the topography are re-scattered by the fractures, especially Rayleigh wave scattering whose amplitudes are much larger than others and making it very difficult to identify effective information from the fractures. 相似文献