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弹性波逆时偏移是当前多分量地震资料相对准确的偏移算法,它能够形成多波模式的成像剖面,从而减少纵波勘探的多解性.本文首先依据各向同性介质中矢量分离纵横波场的速度-应力方程组,利用高阶交错网格有限差分数值方法求解弹性波方程,进而构建矢量的纵波和横波波场,不同于散度和旋度算子分离纵横波场的传统方法,文中提出的矢量分离纵横波场方法保持了原始波场的振幅和相位特征.文中也提出将震源归一化的内积成像条件应用于分离后的纯纵波和横波矢量场,由此得到的转换波成像避免了传统弹性波成像方法中出现的极性反转.水平层状和复杂构造模型测试表明,文中提出的基于矢量分离纵横波场的弹性波逆时偏移方法成像精度高,转换波成像PS和SP极性无反转,所形成的多种模式纯波剖面能够准确地对复杂地下构造成像.
Elastic wave inverse time migration is a relative accurate migration algorithm for multi-component seismic data, which can form multi-wave mode imaging profiles and thus reduce the multiplicity of P-wave exploration.In this paper, based on vector separation of longitudinal and transverse waves in isotropic medium Field velocity-stress equations, the high-order staggered-grid finite difference numerical method is used to solve the elastic wave equation, and then the vector longitudinal and transverse wave fields are constructed. Unlike the traditional method of divergence and rotation operator separating the longitudinal and transverse wave fields, The method of vector separation in both longitudinal and transverse wave fields proposed in this paper preserves the amplitude and phase characteristics of the original wave field. It is also proposed that the inner product imaging normalized by the source be applied to the separated pure P- and S-wave vector fields. Wave imaging avoids the polarity reversal that occurs in the conventional elastic wave imaging methods.Experimental results of the horizontal layered and complex structure models show that the proposed method based on the vectorial separation of the longitudinal and transverse wavefields has the advantages of high imaging accuracy, There is no reversal of the polarities of the PS and the SP in the imaging, and the resulting purely pure-wave profiles of the PS and SP can accurately image complex subsurface structures.