The irregular free surface topography has a significant impact on simulations of seismic wave propagation. Therefore, an accurate representation of the irregular free surface is required for an accurate wavefield simulation. We propose an immersed boundary method used in fluid dynamics calculation to simulate acoustic waves with finite-difference in media with irregular surfaces. First, we set the number of ghost layers to half the length of the finite-difference stencil. Then, we define mirror points by orthogonally projecting the ghost points to fractional points below the free surface. We calculate the wavefield at these mirror points using an iterative symmetric interpolation method. Finally, we set the wavefield at the ghost points to the negative value of the wavefield of their corresponding mirror points. The proposed iterative symmetric interpolation method allows computing the wavefield at the mirror points more accurately and stably than the conventional immersed boundary methods. Numerical examples validate the accuracy and stability of this method in seismic forward modelling with strongly varying topography.

中文翻译：

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地震波场建模中不规则表面地形的迭代对称插值沉浸边界方法

不规则的自由表面形貌对地震波传播的模拟有重大影响。因此，对于精确的波场模拟，需要精确表示不规则的自由表面。我们提出一种浸入边界方法，用于流体动力学计算，以模拟具有不规则表面的介质中具有有限差分的声波。首先，我们将重影层的数量设置为有限差分模板长度的一半。然后，我们通过将幻影点正交投影到自由表面以下的分数点来定义镜像点。我们使用迭代对称插值方法计算这些镜面点处的波场。最后，我们将重影点处的波场设置为其相应镜像点的波场的负值。与传统的浸入边界方法相比，所提出的迭代对称插值方法可以更精确，更稳定地计算镜面点处的波场。数值算例验证了该方法在地形变化剧烈的地震正演模拟中的准确性和稳定性。