起伏地表复杂近地表地质条件下的地震全波形反演

本项研究聚焦于起伏地表、复杂近地表地质条件下的高效稳定的全波形层析反演方法。地震全波形层析反演具有重构高分辨率速度图像的能力，但主流研究考虑的仍然是水平地表情形。本项目依序从三个方面开展攻关。首先，研究起伏地表条件下的贴体网格剖分方法，不仅保持贴体曲网格的正交性，并且保持相邻网格间的对应关系，既解决起伏边界的精确刻画问题，也有利于有限差分算法的实现。第二，根据起伏地表条件下物理空间与计算空间的对应关系，建立计算空间的波动方程以及起伏地表的吸收边界方程，探索起伏地表条件下的有限差分波动方程正演模拟方法。第三，研究频率域波形层析反演方法，频率域实现不仅使得吸收边界的处理更为简捷，同时将提高全波形反演的计算效率。本项目研究的复杂地表地质条件下、贴体曲网格有限差分实现的、频率域波动方程的全波形层析反演方法,将对层析成像反演理论的发展和完善做出重要贡献。

This project will focus on the research of the efficient and stable full waveform inversion for irregular topography and complex near-surface velocity model. Full waveform inversion is capable to reconstruct subsurface velocity models with high resolution, however, only flat surface condition is considered currently in literatures and research communities. The objectives of this project are consisted of the following three sequential steps: (1) Research on model partitioning using body-fitted grid scheme, which will satisfy grid orthogonality and keep the same relationship between neighboring grids as they are in the Cartesian coordinate. It is capable to accurately present irregular topography, and meanwhile is convenient for finite-differencing implementation. (2) Establishing wave equation and the corresponding PML absorbing boundary condition for irregular topography, based on the relationship between the physical coordinates and computational coordinates, and implementing finite-difference forward modelling. (3) Study on frequency-domain full waveform inversion algorithm. In the frequency domain, realization of the absorbing boundary condition will be straightforward, and the efficiency of full waveform inversion will be improved. Overall, this research has the potential to lead to a significant step forward for the theory of full waveform inversion, as we will develop a method with finite-difference simulation, body-fitted grids and frequency-domain implementation, for full waveform inversion with the irregular topography and complex near-surface geological condition.