分层映射法起伏自由地表弹性波正演模拟与波场分离

Elastic wave forward modeling and wave-field separation of irregular free-surface based on the layered mapping method

传统有限差分方法在处理起伏自由地表时存在一些问题;传统映射法通过将起伏地表映射为水平地表克服上述缺点,但在变换的同时会破坏原有地下构造,导致波传播的不准确和虚假反射的产生。为此,通过改进传统映射法,提出了分层映射法起伏自由地表弹性波正演模拟与波场分离方法,在实现算法的基础上,对几个典型起伏地表模型进行了正演模拟试算,结果表明:1分层映射法不仅可以将起伏地表映射为水平地表,而且也可以将地下起伏地层映射为水平地层。相对于传统矩形网格以及常规映射法,分层映射法对双复杂构造具有更好的适应性。2通过对比分层映射法、传统映射法、传统有限差分法的正演模拟试算结果表明,分层映射法具有更高的模拟精度和抑制频散能力。3基于分层映射法的起伏自由地表弹性波波场分离能够准确地将纵、横波分离,可为起伏自由地表弹性波偏移成像方法提供关键的技术支持。

Conventional finite difference method has some difficulties to deal with irregular free-surface.Conventional mapping method can overcome the disadvantage by transforming irregular surface to horizontal surface.But at the same time,the interface below the surface will be destroyed,resulting in inaccurate wave propagation and false reflection.Thus we improve the conventional mapping method and propose an elastic wave forward modeling and wave-field separation of irregular free-surface based on layered mapping method.After realizing the algorithm,several typical irregular free surface models are tested with the seismic forward modeling.The results suggest that:A.The layered mapping method can transform both the irregular surface and interface to horizontal surface and interface.Compared with conventional rectangular grids and conventional mapping method,the layered mapping method has a better adaptability for dual-complex structure;B.Forward modeling comparison tests prove that the layered mapping method has higher simulation accuracy and a better ability of suppressing dispersion;C.The wavefield separation of irregular free-surface based on layered mapping method can accurately separate Pand S-wave,which can provide a key approach for the irregular free-surface elastic imaging.