中間漸移層がある場合の弾性波の反射及び透過

抄録

Reflection and refraction of elastic waves at a discontinuous boundary in transmitting medium have been studied by many authors since 1899. Most of them have assumed that density or elastic constant of the medium vary discontinuously (mathematically) at the boundary. While there can be little doubt that very sharp discontinuities exist in the earth, it will be better to consider that physical properties of materials in the immediate vicinity of the “discontinuity” vary continuously in actual cases. In such cases, the most pertinent transfer of energy among the waves concerned takes place near the boundary, say, within a few wave-lengths from it, and no theory can be adequate without referring to the sharpness of discontinuity as compared with the wave-length.
K. Sezawa and K. Kanai, in 1935, and A. Wolf, in 1937, are the only two who investigated the effect of sharpness of discontinuity on reflection and refraction phenomena. Their studies, however, were confined only to vertical incidence of waves, (although, in the latter, some qualitative statements were made about the general case), with simplifying assumptions that densities are the same everywhere and rigidity or velocity in the intervenient layer varies linearly with depth.
In this paper, the present writer has investigated reflection and transmission of elastic waves at “discontinuity” for the incidence of SH-waves with various glancing angles, supposing that there is an invervenient layer of thickness H between two different media. In the intervenient layer, both density and rigidity vary continuously but steeply from the corresponding values of the upper medium to those of the lower one. He has found that the reflected wave is considerably affected by the existence of the intervenient layer if the wave-length of incident wave is very small compared with the thickness of the layer, but the transmitted wave is not affected very much.