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井间地震数据直达波走时层析成像 总被引:1,自引:0,他引:1
本文利用矢量射线追踪正演模拟技术计算地震波直达波传播的路径及走时,进而利用射线走时及路径的内插,发展了弯曲射线迭代反演技术.该方法可用来重建井间地层的速度图像.基于所发展的方法,我们对较为复杂的典型地质模型进行了井间速度重建.结果表明该方法是一项快速、高精度的走时层析成像技术. 相似文献
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地震射线追踪方法技术在地震学领域有着较为广泛的应用,然而大多数算法建立在直角坐标系或球坐标系下,实际地球并非完美的球体,而是两极略扁的椭球体,因此,球坐标系下计算结果与真实情况存在一定误差.传统的做法一般是在球坐标系下进行计算,而后进行椭球校正.本文提出了一种直接在椭球体模型中采用分区多步最短路径算法进行多震相地震射线追踪的方法技术,实现了椭球坐标系下多震相地震波射线路径追踪和走时计算.与解析解的对比表明:该算法具有较高的计算精度,适用于任意形状的椭球体,且不需要进行额外的走时校正.数值模拟结果表明,计算所得P波和PcP反射波的走时与AK135走时表的误差小于0.1 s.当震中距较大时,使用球对称模型和椭球体模型计算所得的走时差异显著,说明采用椭球坐标系的必要性. 相似文献
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实际地层中地震波传播普遍存在速度和衰减各向异性现象,研究黏弹各向异性介质中高频地震波传播理论有助于揭示地震波的传播特征.本文针对黏弹性VTI介质,从Christoffel矩阵的解析特征值出发推导出qP、qSV和qSH波的复相速度和复射线速度的解析表达式,并应用实射线追踪方法确定出均匀复射线速度矢量,由此计算出实射线速度和实射线衰减以及实射线品质因子.基于非均匀复相速度和均匀复射线速度的解析表达式,推导了实射线慢度和实射线衰减关于黏弹性模量(包括弹性模量和Q值)的敏感度核函数,该敏感度核函数反映各个黏弹性模量对地震波复走时的影响程度.不同岩石样本的数值计算结果显示,实走时对弹性模量更为敏感,而射线衰减(虚走时)对弹性模量和Q值的敏感程度相当.本研究可为黏弹性VTI介质中地震射线追踪和复走时层析成像提供理论基础. 相似文献
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实际地层中传播的地震波普遍存在速度各向异性和能量衰减现象,因此基于弹性介质假设条件下的地震射线正反演算法具有一定的局限性,而研究黏弹性各向异性介质中的地震波传播规律可为揭示地下结构提供更加可靠的理论依据.射线追踪技术是揭示高频地震波传播特性的有效手段之一,然而绝大多数研究仅限于弹性介质.针对黏弹性各向异性介质,本文首先给出了一种射线速度和振幅衰减的计算方法,然后结合改进型最短路径算法,在实空间内实现了计算复杂介质模型中地震波(qP,qSV,qSH)的射线路径和传播走时以及能量衰减(虚走时).该算法适用于复杂黏弹性各向异性介质.误差分析结果显示,实走时的最大相对误差小于0.13%,虚走时的最大相对误差小于0.55%,表明该算法具有较高的计算精度. 相似文献
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射线追踪是地震波走时层析成像的基础,射线空间位置的准确性及射线走时的精度决定了层析成像的可靠性.本文根据哈密尔顿系统可以有效提高程函方程解稳定性的特性,采用辛几何算法(SAM-Symplectic Algorithm Method)及二维三次卷积插值技术进行地震波射线追踪.由于采用了SAM算法,保证了地震波波前精度,提高了射线空间位置的准确性.数值模拟结果表明SAM既能保证哈密尔顿系统的稳定性又具有运算速度快的特点,提高了射线追踪的计算精度. 相似文献
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最短路径射线追踪算法,用预先设置的网络节点的连线表示地震波传播路径,当网络节点稀疏时,获得的射线路径呈之字形,计算的走时比实际走时系统偏大. 本文在波前扩展和反向确定射线路径的过程中,在每个矩形单元内,通过对某边界上的已知走时节点的走时进行线性插值,并利用Fermat原理即时求出从该边界到达其他边界节点的最小走时及其子震源位置和射线路径,发展了相应的动态网络算法. 从而克服了最短路径射线追踪算法的缺陷,大大提高了最小走时和射线路径的计算精度. 相似文献
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在许多地震反演和偏移成像方法中,都要涉及到射线路径和旅行时的计算.本文将波前面三角形网格剖分和三维波前重建法射线追踪技术结合使用,实现了射线路径和旅行时的准确快速计算.三维波前重建法射线追踪过程中可以保证稳定合理的射线密度,克服了常规射线追踪方法存在阴影区的问题.波前面三角形网格剖分在描述和拆分波前面时更加准确有效,而且不需太多的网格数目,从而提高了射线追踪的精度和效率.该方法在三维复杂构造成像方面有独特的优势,目前在实际的Kirchhoff 偏移中的已经有相关应用. 相似文献
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Emil Blias 《Geophysical Prospecting》2013,61(3):574-581
I introduce a new explicit form of vertical seismic profile (VSP) traveltime approximation for a 2D model with non‐horizontal boundaries and anisotropic layers. The goal of the new approximation is to dramatically decrease the cost of time calculations by reducing the number of calculated rays in a complex multi‐layered anisotropic model for VSP walkaway data with many sources. This traveltime approximation extends the generalized moveout approximation proposed by Fomel and Stovas. The new equation is designed for borehole seismic geometry where the receivers are placed in a well while the sources are on the surface. For this, the time‐offset function is presented as a sum of odd and even functions. Coefficients in this approximation are determined by calculating the traveltime and its first‐ and second‐order derivatives at five specific rays. Once these coefficients are determined, the traveltimes at other rays are calculated by this approximation. Testing this new approximation on a 2D anisotropic model with dipping boundaries shows its very high accuracy for offsets three times the reflector depths. The new approximation can be used for 2D anisotropic models with tilted symmetry axes for practical VSP geometry calculations. The new explicit approximation eliminates the need of massive ray tracing in a complicated velocity model for multi‐source VSP surveys. This method is designed not for NMO correction but for replacing conventional ray tracing for time calculations. 相似文献
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立体层析成像是一种新的地震反射波层析成像方法,能为叠前深度偏移提供较为精确的宏观速度模型。本文研究了立体层析成像的实现方法,包括斜率与走时数据的拾取、离散速度模型构建和初始化、射线参数的确定、斜率和走时及射线计算以及反演问题解法等,建立立体层析成像的算法流程。并通过对Marmousi模型试验,对立体层析成像运行所需的主要参数,如初始速度模型、拾取数据量、离散网格尺寸、速度平滑权重等进行测试和分析,总结这些不同参数对立体层析反演结果的影响规律,用以指导生产实践。 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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在地震层析研究中,常常涉及地震波在非均匀介质中的传播路径问题,故快速射线追踪是不可缺少的工具。本文讨论了一种以三点法为基础的逐步逼近的射线追踪方法,其优点是计算速度快、精度高,适合地震层析研究的计算要求。 相似文献
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A fast and global two point low storage optimization technique for tracing rays in 2D and 3D isotropic media 总被引:1,自引:0,他引:1
We present the problem of tracing rays in 2D and 3D heterogeneous isotropic media as a set of optimization problems. Each optimization problem is obtained by applying Fermat's principle to an approximation of the travel time equation from a fixed source to a fixed receiver. We assume a piecewise linear ray path that simplifies the computations of the problem, in the same way Mao and Stuart suggested in a very recent paper. Here, instead, the reflector geometry and the velocity function are computed by using nonuniformly biharmonic splines. On the other hand, to solve the optimization problem we use the Global Spectral Gradient method. This recent developed optimization scheme is a low storage optimization technique that requires very few floating point operations. It only requires the gradient of the travel time function, and it is global because it converges independently of the initial guess, that is, it does not require a close initial ray path. These three properties of the optimization method and the assumption of piecewise linear rays make this ray tracing scheme a very fast, global and effective method when estimating velocities via tomography. Moreover, in a homogeneous stratified or dipped media, any solution of the optimization problem is the best solution, i.e., it is the global minimum, no matter what numerical approach is used. We present some numerical results that show the computational advantages and the performance of this ray tracing in homogeneous and heterogeneous media. 相似文献
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Travel time computations using a compact eikonal equation for vertical transverse isotropic media 下载免费PDF全文
Eikonal solvers often have stability problems if the velocity model is mildly heterogeneous. We derive a stable and compact form of the eikonal equation for P‐wave propagation in vertical transverse isotropic media. The obtained formulation is more compact than other formulations and therefore computationally attractive. We implemented ray shooting for this new equation through a Hamiltonian formalism. Ray tracing based on this new equation is tested on both simple as well as more realistic mildly heterogeneous velocity models. We show through examples that the new equation gives travel times that coincide with the travel time picks from wave equation modelling for anisotropic wave propagation. 相似文献