多轴复频移近似完全匹配层弹性波模拟

Multi-axial complex-frequency shifting nearly perfectly matched layer for seismic forward modeling in elastic media

在地震正演模拟中完全匹配层是现今吸收效果最好、应用最广的边界条件。由分裂法发展到各种非分裂方法,很大程度上提升了完全匹配层的计算效率并减少所需内存。近似完全匹配层是一种直接对波场进行变换的新型非分裂方法,相比卷积完全匹配层具有不改变方程形式且易于实现等优势,但无法吸收掠入波和瞬逝波,因此目前仍以卷积完全匹配层为主。本文在近似完全匹配层边界处理技术的基础上引入复频移技术,实现了对大角度入射波和极低频波的吸收;采用多轴技术提升近似完全匹配层的稳定性;引入新的衰减函数以整体提升近似完全匹配层吸收效果。最终使近似完全匹配层能够更稳定有效地吸收任意入射波。

The perfectly matched layer(PML)is a very efficient method and has become widely used in the seismic forward modeling.The development from split methods to various non-split methods greatly improves the computational efficiency of PML and reduces the required memory.The nearly perfectly matched layer(NPML)belongs to nonsplit PML,and it transforms directly the wavefield.Therefore,it does not change the form of the governing equations and is easy to be implemented.However,the NPML suffers from large spurious reflections at grazing incidence and evanescent wave.So,the convolution perfect matching layer(CPML)is still usually used.We implement the complex frequency shifted-NPML(CFS-NPML)to improve the capacity of absorbing grazing-incidence wave.We introduce different damping profiles that are proportional to each other in the orthogonal direction to make CFS-NPML stable called multi-axial CFS-NPML(MCFS-NPML).Meanwhile we design a new attenuation function which can improve the NPML absorption further.Eventually,the MCFS-NPML is able to absorb any incident wave more stably and efficiently.