基于声波方程的有限频伴随状态法初至波旅行时层析

First arrival tomography with finite frequency adjoint-state method based on acoustic wave equation

根据有限频理论,对于特定震相的观测信息,不仅射线路径上的介质对该信息具有影响,路径以外的其它区域对接收信息也具有影响,这种影响可以用核函数来表达。传统核函数的计算是基于"波路径"的,计算繁琐且效率低。而基于射线理论的伴随状态法虽然可以在很大程度上提高反演效率,却没有考虑地震波传播的有限频特性,这就导致了反演过程中低波数信息的缺失。本文基于伴随状态法,同时考虑地震波传播的有限频特性,研究并实现了基于声波方程的有限频伴随状态法初至波旅行时层析成像。将该方法应用于表层速度结构反演,理论模型实验表明,该方法比传统非线性射线旅行时层析成像具有更高的反演精度。

According to finite-frequency theory,for a single source-receiver pair,not only the media on the raypath but also those outside the ray affects the wave propagation.This kind of effect can be described by sensitivity kernel which is always calculated based on'wavepath' with low efficiency.While the adjoint-state method based on ray theory ignores the finite-frequency characteristics of wave propagation,which leads to poor imaging.In this paper,we propose a new approach which combines the adjoint-state method and finite-frequency theory.Numerical experiments using it in near-surface velocity structure inversion indicate that the proposed approach can achieve results with higher accuracy than the traditional nonlinear ray-based tomography method.