【作者】 陈秀梅； 李幼铭； 杨长春；

【Author】 Chen Xiumer (Tongji University,Shanghai,200092) Li Youming Yang Changchun (Institute of Geophysics,Chinese Academy of sciences,100101)

【机构】 同济大学海洋系； 胜利油田计算中心开发室； 中国科学院地球物理研究所；

【摘要】 地震走时的计算一般有两类方法,一类是射线追踪,另一类是波前法。波前法通过模拟波前面的传播直接计算网格节点的走时。早期的走时差分算法往往比较复杂且不能向量化,甚费机时,如Vidale(1988)差分法。1991年Van Trier和Symes提出了一种精细的能完全向量化的二维逆风算法,该算法具有精确快速稳定的优点。Popovici(1991)不久将Trier-Symes二维逆风算法推广到三维。Schneider(1995)改进了Popovici (1991)算法的稳定性,并导出了三维稳定条件。然而由于他们均是在三维球坐标下实现逆风法,需要在球坐标和笛卡儿坐标之间对走时和慢度场进行转换和内插,因而增加了算法的复杂性。本文提出了一种在笛卡儿坐标下实现的三维逆风有限差分算法,它克服了Popovici(1991)和Schneider(1995)球坐标方法的上述缺陷,提高了算法效率。同时,基于Neumann分析原理推导了本文算法的稳定条件,实现了算法自适应稳定性。该算法精确、稳定和高效。理论计算和实际应用结果表明,本方法能很好地适应高反差的复杂速度介质。更多还原

【Abstract】 There are generally two classes of methods to calculate seismic traveltimes.One is ray tracing and the other is wavefront method.By mimicking wavefront propagation,wavefront method can fast computes traveltimes at grid points.Earlier traveltime difference methods like Vidale’s(1988) were usually complicated and unvectorizable,thus taking much runtime.Van Trier and Symes in 1991 put forward a two-dimensional upwind method which is accurate,efficient,stable and vectorizable.Later in the same year Popovici expanded this method to three dimensions.In 1995,Schneider improved Popovici scheme in stability and derived stability condition in three dimensions.Popovici and Schneider both performed their schemes in three-dimensional spherical coordinate system,which need to map and interpolate slowness and traveltime fields between spherical and Cartesian coordinate systems,thus adding complexity to their algorithms.This paper presents an 3D upwind method realized directly in Cartesian coordinate system.It overcomes the above drawbacks of Popovici and Schneider methods and thus enhances efficiency.In addition,the paper also derived the corresponding stability condition based on Neumann’s regulations to realize the auto-adaptive stable step length. The theoretical and practical calculating results prove that this technique can be well applicable to high-contrast complicated velocity media.更多还原