高阶高密度三维多波多分量弹性波波场分离正演数值模拟

High-order high-density 3D multi-wave multi-component elastic wave field separating forward numerical simulation

针对二维全波场弹性波模拟无法准确表征真实的三维地球介质波场响应,为此首次开展了三维弹性波全波场波场分离正演数值模拟研究,该方法是全面认识和研究地震波在三维地球介质中传播规律的重要手段。从三维一阶速度—应力弹性波波动方程出发,采用高阶(16阶)交错网格有限差分法和内外侧镶边法PML吸收边界条件,并结合了基于散度和旋度原理的三维空间高阶波场分离算子。以三维地质模型为例,设计模拟了野外地表多分量地震资料的采集、零偏移距和非零偏移距VSP记录的采集,开展了三维弹性波全波场高精度、高密度正演数值模拟,并对计算结果进行了三维立体显示。从理论分析和数值试验均表明,文中方法的模拟结果中包括3个多分量混合波场、1个纯纵波波场和3个纯横波波场,在三维弹性波波场快照和模拟记录中均可以容易识别和追踪出各个地层反射界面的反射波和转换波等复杂波场,且计算结果的精度较高,边界吸收较好,采用的三维弹性波波场分离模拟方法还可为实际多波多分量地震资料波场分离方法的准确有效性和三维多波多分量弹性波逆时偏移成像提供方法指导,该方法研究在多波多分量地震勘探中具有一定的推广价值。

For the reason that the 2D full elastic wave simulation method cannot correctly depict the real 3D earth medium＇ s wave responses, 3D full elastic wave field separating forward numerical simulation is carried out, which is the important mean of comprehensively recognize and study the seismic wave＇s propagating law in 3D earth medium. This paper started from 3D first order velocitystress elastic wave equation, used high-order （16th） staggered grid finite difference method and PML absorbing boundary condition of inside and outside bordering method and combined with 3D high-order spatial wave separating operator based on divergence and curl law. Taking 3D geologic model as an example, this paper designed and simulated acquisition of the field surface multi-component seismic data, zero offset VSP records and nonzero offset VSP records, and then carried out the high-accuracy high-density forward numerical simulation of 3D full elastic wave fields, and used 3D visualization on the computational results. The theoretical analysis and the numerical experiments showed that the simulation results contained three multi-component hybrid wave field, one pure compress wave field and three pure shear wave field. Every formational interface＇ s complex wave field such as reflective waves and transformation waves could be obviously recognized and traced within 3D elastic wave snapshots and numerical records. The computed results had perfect numerical accuracy and boundary absorbing effect. The adopted 3D elastic wave field separating method could also guide for the accurate and effective of the practical multi-wave multi-component seismic data wave field separating method and the reverse-time migration imagery. This method could be extended in multi-wave multi-component seismic prospecting.