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2. G. I. Petrashen, “Fundamentals of the mathematical theory of the propagation of elastic waves,” in Questions of the Dynamic Theory of Seismic Wave Propagation (Nauka, Leningrad, 1978), p. 18 [in Russian].
3. V. B. Poruchikov, Methods of Dynamic Theory of Elasticity (Nauka, Moscow, 1986) [in Russian].
4. S. L. Sobolev, “Some questions of the theory of the propagation of oscillations,” in Differential and Integral Equations of Mathematical Physics, Ed. by F Frank and R Mises (ONTI, Moscow, Leningrad, 1937) [in Russian].
5. H. Lamb, “On the propagation of tremors over the surface on an elastic solid,” Philos. Trans. R. Soc. London, Ser. A 203, 1 (1904).