VTI介质qP波广义高阶屏单程传播算子

High-order one-way generalized-screen propagation operator of qP-wave in VTI medium

本文从VTI介质弹性波波动方程入手,通过本征值方法及声学理论近似建立了VTI介质qP波频散关系方程,再根据介质扰动理论深入研究了VTI介质qP波广义高阶屏单程传播算子。将VTI介质参数场分解为均匀各向异性速度场、速度扰动场以及各向异性参数扰动场,这样qP波广义高阶屏单程传播算子就由背景介质波场自由传播项和各向异性扰动项两部分组成。背景场的计算在波数域完成,而非均匀各向异性扰动项(包括慢度扰动项、各向异性参数扰动项)在空间域计算。当各向异性参数横向变化较为剧烈时,采用高阶屏算子能提高单程qP波高角度传播精度。均匀各向异性介质和复杂各向异性介质模型脉冲响应试验表明:qP波广义高阶屏算子不仅在大角度传播时能够满足精度要求,而且能够适应任意强横向变速、强横向各向异性扰动时的情况,适用于复杂VTI介质qP波地震深度偏移。

Starting from elastic wave equation in VTI medium and through eigenvalue equation and acoustic wave theory,the paper approximately created dispersion equation of qP-wave in VTI medium and deeply studied high-order one-way generalized-screen propagation operator of qP-wave in VTI medium based on disturbed theory of medium.Dissolving the parameter field in VTI medium into uniform anisotropic velocity field,velocity disturbed field and anisotropic parameter disturbed field,the high-order one-way generalized-screen propagation operator of qP-wave is composed of two parts: free propagation item of wavefield in background medium and anisotropic disturbed item.The computation of background field is implemented in wavenumber domain and non-uniform anisotropic disturbed item (including slowness disturbed and anisotropic parameter disturbed items) is computed in space domain.When violent lateral variation of anisotropic parameters takes place,using high-order screen operator can improve the propagation precision of one-way qP-wave in steep dip.It is shown by pulse response tests of models in uniform anisotropic medium and complex anisotropic medium that the high-order generalized-screen operator of qP-wave can not only meet the needs of precision,but also adapt to any strong lateral velocity variations and anisotropic disturbance,which is suitable for seismic depth migration of qP-wave in VTI medium.