The questions of uniqueness and existence of subsonic Stoneley waves in bonded anisotropic linear elastic half-spaces are settled by using the notion of the interface impedance tensor, which is a simple linear combination of the hermitian surface impedance tensors of the separate half-spaces. A definite existence criterion is presented in a form that proves most useful in numerical searches for Stoneley waves, in the sense that such searches need not be conducted when a Stoneley wave mode does not exist.

No abstract

General equations in stress and displacement are set down and their implications qualitatively discussed.Detailed results are presented for the slownesses, amplitudes and energy fluxes of body waves generated by the incidence of a body wave upon a range of differently oriented boundaries in hexagonal media.Results for ice and beryl show that assumption of isotropy preserves the qualitative form of the reflexion characteristics; in contrast, the variations caused by changing the orientation of the boundary in zinc are too great to be adequately represented in terms of isotropicconstants.

Two additional criteria for the existence of cusp points on elastic wave surfaces are developed.A previously published method [1] is extended to give a simple necessary and sufficient condition for cusps about (1, 1, 0) axes in cubic and tetragonal media. This criterion is plausibly adapted to provide a simple inequality applicable to any section of slowness surface represented by separable quadratic and quartic equations.Two tables of numerical examples are presented.

Consideration of the direction of the normal at any point on a continuous sheet of a surface yields a sufficient condition for the existence of parabolic points on that sheet. This condition has been used to derive some simple inequalities between elastic constants, whose fulfilment determines the existence of parabolic points upon the inverse surfaces of media of orthorhombic, tetragonal, cubic or hexagonal symmetry; in virtue of the polar reciprocal relation between inverse and wave surfaces, the existence of cusp points on the latter is thereby simultaneously established. It is also pointed out that conditions for external conical refraction may prevail in hexagonal media.