How do you calculate the Rayleigh velocity?

If you have an isotropic material, the phase velocity of the surface wave (Rayleigh wave)can be approximately calculated by the following equation: v ~ [(0.72-(v_t/v_l)^2)/(0.75-(v_t/v_l)^2)]) * v_t where v is the Rayleigh velocity v_t is the transverse wave velocity (v_t=sqrt(c_44/density)) v_l is the longitudinal wave velocity(v_l=sqrt(c_11/density) and c_11 and c_44 are the members of the elastic constant tensor. For anisotropic materials, each direction of propagation possesses its own velocity and things get more complicated.