Approximation to Cutoffs of Higher Modes of Rayleigh Waves for a Layered Earth Model
Approximation to Cutoffs of Higher Modes of Rayleigh Waves for a Layered Earth Model
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DOI：
10.1007/s00024-008-0443-4
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发表时间：
2009-02
影响因子：
2
通讯作者：
Yixian Xu;J. Xia;Richard D. Miller
中科院分区：
文献类型：
--
作者：
Yixian Xu;J. Xia;Richard D. Miller
截止定义了瑞利波高阶模的长周期终止，因此是高阶模能量与地下几种材料性质关系的关键特征。截止已被用来估计剪切波速度的层状地球模型的下伏半空间。在这项研究中，我们描述了一种方法，取代多层地球模型与一个单一的表面层覆盖的半空间模型，完成谐波平均速度和算术平均密度。通过与理论模型的数值比较，验证了单层近似。该单层近似的准确度最好由截止处的频率和相速度估计中的计算误差的值来定义。我们提出的方法直观地解释了射线理论。数值结果表明，瑞利波通过深度内的平均弹性性质和下伏半空间的剪切波速度控制的截止频率。
A cutoff defines the long-period termination of a Rayleigh-wave higher mode and, therefore is a key characteristic of higher mode energy relationship to several material properties of the subsurface. Cutoffs have been used to estimate the shear-wave velocity of an underlying half space of a layered earth model. In this study, we describe a method that replaces the multilayer earth model with a single surface layer overlying the half-space model, accomplished by harmonic averaging of velocities and arithmetic averaging of densities. Using numerical comparisons with theoretical models validates the single-layer approximation. Accuracy of this single-layer approximation is best defined by values of the calculated error in the frequency and phase velocity estimate at a cutoff. Our proposed method is intuitively explained using ray theory. Numerical results indicate that a cutoffs frequency is controlled by the averaged elastic properties within the passing depth of Rayleigh waves and the shear-wave velocity of the underlying half space.