Further criteria for elastic waves in anisotropic media

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.