Rayleigh waves in an anisotropic elastic medium and impedance

In the paper, the impedance operator, its properties and relationships with the Rayleigh waves in anisotropic media are considered. Zero eigenvalues of the impedance operator determine the Rayleigh waves in the anisotropic media. This property give us a possibility to prove the uniqueness theorem for the Rayleigh wave in any anisotropic medium close to isotropic one.