APPENDIX A

In this appendix, I show the explicit form of the coefficients a_i in equation (8).

$$\begin{eqnarray} a_0 & = & c^4 p^4 - T_{0}^{2} \nonumber \\ a_1 & = & -2T_0 T_1 ... ...4}) (c_{33}- c_{44})- (c_{13} + c_{44})^2] / \rho^2 \\ \nonumber\end{eqnarray}$$ (12)

where c_ij are four of the five elastic constants that describe an homogeneous transversely isotropic medium, $\gamma_2$ is the orientation of the axis of symmetry measured from the normal to the interface, p is the ray parameter and $\rho$ is the density.