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横向各向同性介质是地球内部广泛分布的一种各向异性介质.针对这种介质，我们对各向同性介质的最小走时树走时模拟方法进行了推广，推广后的方法可适用于非均匀、对称轴任意倾斜的横向各向同性介质模型.为保证计算效率，最小走时树的构建采用了一种子波传播区域随地震波传播动态变化的改进算法.对于弱各向异性介质，我们使用了一种新的地震波群速度近似表示方法，该方法基于用射线角近似表示相角的思想，对3种地震波（qP, qSV和qSH）均有较好的精度.应用本文地震波走时模拟方法对均匀介质、横向非均匀介质模型进行了计算，并将后者结果与弹性波方程有限元方法的模拟结果进行了对比，结果表明两者符合得很好.本文方法可用于横向各向同性介质的深度偏移及地震层析成像的深入研究. 相似文献
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本文主要研究了黏弹性HTI和EDA介质中地震波的波动参数(包括相速度、慢度、偏振向量和群速度),并基于摄法,推导了P、SV、SH波波动参数的弱各向异性近似公式.文章提出了慢度向量的三种定义形式,分析对比了各种定义方法在求解christo-ffel方程时的具体方法,指出特殊分量法为各向异性黏弹性介质提供了一种研究均匀和非均匀波的更简单、使用更普遍的方法.基于特殊分量法,通过求解christoffel方程,推导出黏弹性HTI介质中均匀、非均匀波的精确相速度、慢度和群速度计算公式,并通过模型计算研究了SH波的相速度特征及其随相角和不均匀参数D的变化规律,结果表明参数D对地震波的相速度大小有一定影响,但对其方位特性无影响,在EDA介质中相速度随方位角变化的规律仍然可指示介质的对称轴方向和裂隙的走向.基于摄动法,以弹性EDA介质为背景介质,通过模型计算对均匀SH波的近似公式的正确性和精度进行验证,结果证明其最大相对误差为1.15%. 相似文献
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用慢度分块均匀正方形模型将介质参数化，仅在正方形单元的边界上设置计算结点，这些结点构成界面网．根据Ｈｕｖｓｅｎｓ和Ｆｅｒｍａｔ原理，由不断扩张、收缩的波前点扫描代替波前面搜索，在波前点附近点的局部最小走时计算中对波前点之间的走时使用双曲线近似，通过比较确定最小走时和相应的次级源位置，记录在以界面网点位置为指针的３个一维数组中．借助这些数组通过向源搜索可计算任意点（包括界面网以外的点）上的全局最小走时和射线路径．这一方法不受介质慢度差异大小限制，占内存少，计算速度较快，适于走时反演和以Ｍａｓｌｏｖ射线理论为基础的波场计算． 相似文献
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任意介质中的动态规划法地震波三维走时计算 总被引：1，自引：1，他引：1
任意介质中的地震波三维走时计算是复杂介质情况下Kirchhoff积分法三维叠前深度偏移及走时层析成像的核心.走时算法的效率及精度决定了成像方法的应用范围及效果,对复杂地质构造区域的地震波成像时需要有稳健的走时计算方法.本文把Schneider等提出的用动态规划法计算二维任意复杂介质中走时的方法推广到三维.此方法的核心是构造从源点到当前计算点的平均慢度,基于Fermat原理,用球面波近似导出走时计算所用的公式,并用动态规划法搜索到达当前计算点的初至走时.它适用于任意复杂的介质情况,对速度差异没有限制,计算过程中考虑到各个可能的方向到达当前计算点的初至波.首波及回转波的初至走时也能正确地计算出来.各种理论速度模型上的走时计算及胜利油田某探区的三维叠前深度偏移的成功实践验证了方法的正确性. 相似文献
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本文基于球谐展开群速度表达式计算走时关于各向异性参数的Fréchet核函数,利用共轭梯度法对两种参数化方法进行了VTI介质中多参数联合反演方法研究.经过理论分析和数值试验发现,与经典的Thomsen参数化方法相比,垂直慢度、水平慢度与动校正慢度的参数化方式更有利于VTI介质多参数联合走时层析反演.为了克服走时对ε参数的不敏感性,我们采用了两步法进行双参数反演,理论模型试验反演得到了与垂直速度精度相当的ε参数.可以将两步法扩展到三步法以同时反演各向异性介质中的三个参数,数值试验展示了该策略的应用潜力. 相似文献
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本文提出了一种利用反射波走时曲线计算垂向非均匀介质速度和反射界面深度的方法。当在地球表面没有获得来自地下某一深度范围内介质的任何信息时,可以认为这一深度范围内的地震波速度具有连续性。利用来自其底部反射界面的反射波走时曲线,可以计算出该深度范围的地震波速度结构。对三种模型进行了理论计算,所得反演解与真实值较为一致,其中计算出的反射界面深度最为精确。利用本文提出的方法可以计算两个相邻反射面之间的垂向非均匀速度结构,如低速层等。 相似文献
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在裂缝诱导各向异性理论研究中通常使用等效HTI介质来近似多组裂缝所引起的综合效应.由于构造运动的复杂性,多组裂缝普遍存在于地壳与油气储层中.为了研究多组裂缝的地震属性特征,分析常用的等效HTI模型对于多组裂缝近似精度及附加裂缝对介质属性特征的影响,本文利用线性滑移模型进行了多组垂直裂缝的单斜各向异性等效介质理论计算,并利用空间搜索方法求取与其最为接近的HTI介质各向异性弹性参数.重点研究了在两种各向异性介质中纵波速度、快慢横波速度和极化特征及其差异,量化分析附加裂缝对于地震属性如速度、极化方向和走时等的影响,研究对附加裂缝敏感的地震属性.此研究结果和方法为进一步研究多组裂缝的反演及识别方法提供基础,同时对于将高阶对称性各向异性介质中已存在的计算方法应用于低阶对称性时的适用程度、精度分析及相关方法研究具有重要作用. 相似文献
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给出了计算多层垂直对称轴横向各向同性（VTI）介质精确射线路径和走时的方法,所用的体波相速度公式、群速度公式和Snell定律都是严格的显式解析公式. 任意基本波的射线路径和走时计算问题都可以转化成一个等效的透射问题,再用文中的公式来计算,具体实现方法用一个多次波和一个首波的实例给出. 最后分别用精确公式和Thomsen近似公式计算了相同模型相同基本波的走时曲线. 比较两者计算结果可发现, 近似公式反复使用会使误差积累,同时揭示了近似公式适用范围的局限性,强调了使用近似公式需要注意其适用范围的重要性. 相似文献
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传统的区域台网定位都是以近震震相的走时方程为依据的.如果没有至少一个震中距小于震源深度的台站存在,是不可能给出震源深度的精确解的.本文建议,在不要求如此严格的条件限制下,利用走时方程和视慢度方程,在速度-深度场中,建立两种位置和形状极不相同的 v-h 曲线簇,曲线的交点确切地同时给出震源深度和介质速度的解.我们能够看到,视慢度的引入对深度的确定,起着很强的约束作用.文中给出了这个方法人工数值模拟的结果和应用实例,并讨论了它的精度和偏移.从理论上讲,走时和视慢度的结合使用,对解决区域台网精确确定震源深度的问题,也许是一条切实可行的途径. 相似文献
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N. V. Petersen 《Pure and Applied Geophysics》1990,132(1-2):417-437
Scattering at random inhomogeneities in a gradient medium results in systematic deviations of the rays and travel times of refracted body waves from those corresponding to the deterministic velocity component. The character of the difference depends on the parameters of the deterministic and random velocity component. However, at great distances to the source, independently of the velocity parameters (weakly or strongly inhomogeneous medium), the most probable depth of the ray turning point is smaller than that corresponding to the deterministic velocity component, the most probable travel times also being lower. The relative uncertainty in the deterministic velocity component, derived from the mean travel times using methods developed for laterally homogeneous media (for instance, the Herglotz-Wiechert method), is systematic in character, but does not exceed the contrast of velocity inhomogeneities by magnitude. The gradient of the deterministic velocity component has a significant effect on the travel-time fluctuations. The variance at great distances to the source is mainly controlled by shallow inhomogeneities. The travel-time flucutations are studied only for weakly inhomogeneous media. 相似文献
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Xiangyang Li Jianxin Yuan British Geological Survey West Mains Road Edinburgh EH LA UK. Formerly at British Geological Survey now at PGS Inc. Richmond Avenue Suite Houston TX USA. 《应用地球物理》2005,2(1)
我们业已研发了计算各向异性、非均质介质中P- SV转换波(C-波)的转换点和旅行时的新理论。据此 可以利用诸如相似性分析、迪克斯模型建模、克契 霍夫求和等常规方法来完成各向异性的处理和各向 异性处理,并使各向异性的处理成为可能。这里将 我们的新发展分作两部分来介绍。第一部分为理 论,第二部分为对速度分析和参数计算的应用。第 一部分理论包括转换点的计算和动校正的分析。 相似文献
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利用在青藏高原东部及其邻近地区记录到的１万余条近震到时资料,反演该地区的地壳上地幔三维速度结构。采用网格点模型描述三维速度结构,模型维数为２２２２６,网格点间距水平向为１００ｋｍ,垂直向为２０ｋｍ,网格点之间的速度值通过线性插值给出。采用改进了的快速三维射线追踪方法,确定三维非均匀介质中的地震射线路径和理论走时。反演结果显示,青藏高原南部的上地壳中（３０ｋｍ左右的深度）存在一低速区,这和面波反演的结果一致,羌塘块体下地壳有明显的低速异常带,青藏公路沿线的垂直速度剖面显示出岩石层受挤压增厚的构造特征。 相似文献
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Paraxial ray methods have found broad applications in the seismic ray method and in numerical modelling and interpretation
of high-frequency seismic wave fields propagating in inhomogeneous, isotropic or anisotropic structures. The basic procedure
in paraxial ray methods consists in dynamic ray tracing. We derive the initial conditions for dynamic ray equations in Cartesian
coordinates, for rays initiated at three types of initial manifolds given in a three-dimensional medium: 1) curved surfaces
(surface source), 2) isolated points (point source), and 3) curved, planar and non-planar lines (line source). These initial
conditions are very general, valid for homogeneous or inhomogeneous, isotropic or anisotropic media, and for both a constant
and a variable initial travel time along the initial manifold. The results presented in the paper considerably extend the
possible applications of the paraxial ray method. 相似文献
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Igor Ravve 《Geophysical Prospecting》2016,64(3):517-542
We suggest a new method to determine the piecewise‐continuous vertical distribution of instantaneous velocities within sediment layers, using different order time‐domain effective velocities on their top and bottom points. We demonstrate our method using a synthetic model that consists of different compacted sediment layers characterized by monotonously increasing velocity, combined with hard rock layers, such as salt or basalt, characterized by constant fast velocities, and low velocity layers, such as gas pockets. We first show that, by using only the root‐mean‐square velocities and the corresponding vertical travel times (computed from the original instantaneous velocity in depth) as input for a Dix‐type inversion, many different vertical distributions of the instantaneous velocities can be obtained (inverted). Some geological constraints, such as limiting the values of the inverted vertical velocity gradients, should be applied in order to obtain more geologically plausible velocity profiles. In order to limit the non‐uniqueness of the inverted velocities, additional information should be added. We have derived three different inversion solutions that yield the correct instantaneous velocity, avoiding any a priori geological constraints. The additional data at the interface points contain either the average velocities (or depths) or the fourth‐order average velocities, or both. Practically, average velocities can be obtained from nearby wells, whereas the fourth‐order average velocity can be estimated from the quartic moveout term during velocity analysis. Along with the three different types of input, we consider two types of vertical velocity models within each interval: distribution with a constant velocity gradient and an exponential asymptotically bounded velocity model, which is in particular important for modelling thick layers. It has been shown that, in the case of thin intervals, both models lead to similar results. The method allows us to establish the instantaneous velocities at the top and bottom interfaces, where the velocity profile inside the intervals is given by either the linear or the exponential asymptotically bounded velocity models. Since the velocity parameters of each interval are independently inverted, discontinuities of the instantaneous velocity at the interfaces occur naturally. The improved accuracy of the inverted instantaneous velocities is particularly important for accurate time‐to‐depth conversion. 相似文献
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Guiting Chen Zhenli Wang Oluwatosin John Rotimi Suyang Zhang 《Geophysical Prospecting》2020,68(4):1314-1327
Conventional Kirchhoff prestack time migration based on the hyperbolic moveout can cause ambiguity in laterally inhomogeneous media, because the root mean square velocity corresponds to a one-dimensional model under the horizontal layer assumption; it does not include the lateral variations. The shot/receiver configuration with different offsets and azimuths should adopt different migration velocities as they contribute to a single image point. Therefore, we propose to use an offset-vector to describe the lateral variations through an offset-dependent velocity corresponding to the difference in offset from surface points to the image point. The offset-vector is decomposed into orthogonal directions along the in-line and cross-line directions so that the single velocity can be expressed as a series of actual velocities. We use a simple Snell's law-based ray tracing to calculate the travel time recorded at the image point and convert the travel time to an equivalent velocity corresponding to a pseudo-straight ray. The double-square-root equation using such an equivalent velocity in the offset-vector domain is non-hyperbolic and asymmetrical, which improves the accuracy of the migration. Numerical examples using the Marmousi model and a wide azimuth field data show that the proposed method can achieve reasonable accuracy and significantly enhances the imaging of complex structures. 相似文献
17.
Fritz Gassmann 《Pure and Applied Geophysics》1964,58(1):63-112
Summary Section 1 (and 11) develops the concepts of the front velocity, the front gradient, the travel time in space and on seismometric profiles, the profile velocity and the profile gradient in connection with the propagation of the fronts of elastic waves in solid isotropic and anisotropic media. The sectional velocity and the sectional gradient are defined in terms of the motion of the curve of intersection of a front with a fixed surface. Section 2 (and 12) relates the coefficients of elasticity of the medium, the front types, and their respective rays. In section 12, the theory of fronts of arbitrary shape and of the corresponding rays for any anisotropic, homogeneous or inhomogeneous solid medium is summarized. In section 3 (and 13), the law of reflection and refraction of fronts on surfaces of discontinuity of arbitrary shape is presented. Sections 4 to 6 (and 14 to 16) treat some elementary applications of seismic travel time methods to homogeneous, uniaxially anisotropic media (=transverse isotropy) in greater detail. In section 4 (and 14), the travel time of a direct front generated by a point source is considered and it is shown how the coefficients of elasticity of the medium can be found based on travel time measurements. The seismic prospection of a plane reflector and of a reflecting boundary of arbitrary shape and position are discussed in section 5 (and 15). In section 6 (and 16), the seismic refraction method is used to locate a plane boundary between a homogeneous, uniaxially anisotropic and a homogeneous isotropic medium, where the boundary is perpendicular or at an arbitrary angle to the direction of anisotropy. 相似文献
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