起伏地表有限元叠前逆时偏移完全匹配层

摘要

Boundary reflection is an important problem of numerical simulation in limited domain. Perfectly matched layer (PML) absorbing boundary condition (ABC) is one of the best choices to eliminate boundary reflection. Generally, forward modeling needn' t consider PML ABC in free surface, but in prestack reverse time migration, false events will be existed due to the free surface reflection. The goal is to derive the PML ABC formulas of second-order finite element acoustic wave equation based on rugged topography in displacement form and apply it in finite element numerical simulation in rugged topography. Several numerical modeling results are compared. The numerical results show that PML ABC based on rugged topography obtains a much better boundary absorption effect than that of CE ABC, which shows the advantages of this method. So it will eliminate the fault events result from the free surface reflection in prestack reverse time migration based on rugged topography.%在地震波传播的数值模拟中,用有限区域代替求解无限区域地震波传播规律是一种有效手段.目前完全匹配层吸收边界条件是边界吸收最好的选择.通常正演模拟不考虑自由表面吸收条件,但在逆时偏移中,地表反射的存在会引起假的同相轴.推导了位移形式的有限元二阶声波方程的完全匹配层吸收边界条件公式,并应用于起伏地表声波方程有限元数值模拟与逆时偏移成像;通过数值分析并与传统的Clayton-Engquist吸收边界条件做了比较.计算结果表明,方法取得了理想的边界吸收效果,可以消除起伏地表反射引起的假同相轴.