Discontinuous-Grid Finite-Difference Seismic Modeling Including Surface Topography
Discontinuous-Grid Finite-Difference Seismic Modeling Including Surface Topography
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DOI：
10.1785/0120000024
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发表时间：
2001-12
影响因子：
3
通讯作者：
K. Hayashi;D. Burns;M. Toksöz
中科院分区：
文献类型：
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作者：
K. Hayashi;D. Burns;M. Toksöz
我们已经发展了一个二维P-SV粘弹性有限差分模拟技术，复杂的表面地形和地下结构。近地表区域地震波传播的真实模拟受到许多因素的影响，如强烈的非均匀性、地形起伏和大的衰减。为了考虑这些并发症，我们使用O（2，4）精度的粘弹性速度-应力交错网格有限差分格式。该实施包括一个不规则的自由表面条件地形起伏和不连续网格技术在模型的浅部。对几种自由液面条件的计算方法进行了对比分析，提出了一种准确、简便的自由液面条件。在建议的自由表面条件下，计算应力，使垂直于边界的正应力和自由表面上的剪应力为零。自由表面处的颗粒速度的计算不涉及任何特定的计算，并且自由表面上方的颗粒速度被设置为零。介绍了一种不连续网格方法，在近地表或低速区域使用比模型其余部分细3倍的网格。为了减少不稳定性，我们应用平均或加权来替换细网格场中的粗网格组件。该方法使我们能够避免任何限制的网格间距边界的形状。数值试验表明，大约10个网格点，每最短波长，计算在粗网格间距，与不连续网格方法的结果，只要少量的时间步长是准确的计算。
We have developed a two-dimensional P - SV viscoelastic finite-difference modeling technique for complex surface topography and subsurface structures. Realistic modeling of seismic wave propagation in the near surface region is complicated by many factors, such as strong heterogeneity, topographic relief, and large attenuation. In order to account for these complications, we use an O(2,4) accurate viscoelastic velocity-stress staggered-grid finite-difference scheme. The implementation includes an irregular free surface condition for topographic relief and a discontinuous grid technique in the shallow parts of the model. Several methods of free surface condition are bench marked, and an accurate and simple condition is proposed. In the proposed free surface condition, stresses are calculated so that the normal stresses perpendicular to the boundary and shear stresses on the free surface are zero. The calculation of particle velocities at the free surface does not involve any specific calculations, and the particle velocities are set to zero above the free surface. A discontinuous-grid method is introduced, where we use a 3 times finer grid in the near surface or low velocity region compared to the rest of the model. In order to reduce instability, we apply averaging or weighting to the replacement of the coarse-grid components within the fine grid field. The method allows us to avoid any limitation of the shape of the grid-spacing boundary. Numerical tests indicate that approximately 10 grid points per shortest wavelength, counted in coarse-grid spacing, with the discontinuous grid method results in accurate calculations as long as a small number of time steps is concerned.