界面波数值模拟及其在海底浅层结构中的应用

The interface wave simulation and its application in the shallow seabed structures

界面波的频散特征与海底介质特性之间存在密切联系,利用界面波频散曲线可反演海底浅层地质结构.首先设计了水平四层均匀介质模型,基于弹性波动方程的交错网格有限差分法模拟了全波场记录,利用时频分析法从正演记录中提取出界面波频散曲线,进而通过非线性贝叶斯反演手段获取海底浅层介质模型参数.结果表明,从模拟记录中提取的界面波频散曲线与理论计算的频散曲线有较好的一致性,验证了界面波正演模拟的准确性和有效性,反演得到的最大后验概率模型与初始设计模型基本吻合,说明非线性贝叶斯算法在界面波反演中的精度较高,最后通过求解参数的1D和2D边缘概率分布,对参数反演结果的不确定性进行了分析.

The dispersion curves can be used to estimate shallow seabed structures and their uncertainties based on the relationship between interface wave dispersion characteristics of and seabed sediment characters. This paper designs a 4-layer parallel, homogeneous and isotropic media model, simulates the seismic wave field recording using staggered-grids finite-difference method based on elastic wave equation, and extracts the interface-wave dispersion curves from seismic wave simulation via the time-frequency analysis. The nonlinear Bayesian inversion method is applied to determine the shallow seabed sediment parameters. The results show there is a good agreement between the dispersion curve extracted from simulation recording and the dispersion curve computed by theoretical modeling, which proves the interface-wave simulation has high precision and effective. The maximum a posterior model and the designed model matches very well, which show that the nonlinear Bayesian method has the high resolution in the interface-wave inversion. The 1D and 2D marginal probability distributions are used to analyze the uncertainties of parameters quantitatively.