起伏层状介质中曲线交错网格有限差分弹性波逆时偏移成像

Time reverse migration based on curvilinear stagger-grid finite difference method

采用曲线网格有限差分法描述复杂起伏地形(或不规则波阻抗界面)时,波场正演中可以避免因阶梯近似导致的虚假散射,进而波场逆时偏移可对起伏地表模型进行准确成像.文中以弹性波逆时偏移理论为基础,求解一阶速度-应力方程,推导出了弹性波正向传播和逆时传播的曲线网格差分格式,使用完全匹配吸收边界压制边界反射,采用互相关成像条件,实现了起伏层状介质中的波场逆时偏移.三层起伏、尖灭模型,以及起伏地表条件下的部分盐丘模型结果表明:曲线网格有限差分法逆时偏移法是一种高效、准确的逆时偏移法.

When describing complex and undulating terrain(or irregular wave impedance interface)by using curvilinear-grid finite difference method,the forward wavefield simulation can avoid of false scattering caused by the ladder approximation.Therefore,the reverse time migration can accurately image the undulating subsurface structure.We in this article solve a one-order velocity-stress equation based on the theory of elastic wave reverse time migration,and deduce the curvilinear-grid finite difference scheme of elastic wave forward modeling and reverse time migration,using perfect match layer absorbing boundary,apply cross-correlation imaging conditions,and finally realize wavefield reverse time migration in the presentation of the undulating layer medium.The results of the undulated three-layer,interface merger model and the undulated part of salt mode show that the curvilinear-grid finite difference method is an efficient and accurate reverse time migration method.