In an elastic model with orthorhombic (ORT) symmetry, there are nine independent stiffness coefficients that control the propagation of all intrinsically coupled wave modes. For practical applications in P-wave modeling and inversion, it is important to derive the approximate solutions that support propagation of P-waves only and depend on fewer independent parameters. Due to the increasing interest in S-wave propagation in anisotropic media, we also derive an approximate equation that supports propagation of S-waves only. However, the reduction in the number of independent parameters for the S-wave equation is not possible. We derive pure P- and S-wave equations in an elastic ORT model and find that the accuracy is sufficient for practical applications.

中文翻译：

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弹性正交介质中的纯模式 P 波和 S 波相速度方程

在具有正交 (ORT) 对称性的弹性模型中，有九个独立的刚度系数控制所有固有耦合波模式的传播。对于 P 波建模和反演的实际应用，重要的是推导出仅支持 P 波传播并依赖较少独立参数的近似解。由于对各向异性介质中 S 波传播的兴趣日益增加，我们还推导出了一个仅支持 S 波传播的近似方程。然而，减少 S 波方程的独立参数的数量是不可能的。我们在弹性 ORT 模型中推导出纯 P 波和 S 波方程，发现精度足以满足实际应用。