Lg, Li and Rg from Rayleigh Modes

We demonstrate in terms of group velocities and surface amplitude displacements, that the vertical and longitudinal component of the Lg wave can be identified with higher Rayleigh modes for crustal sources. Low velocity layers in the crust are not required for the existence of Lg waves. Li could be used as a sufficient but not necessary discriminant for structures containing a low velocity channel in the upper mantle. Analogous group velocity and amplitude reasoning applies to Rg waves generated by crustal shocks; such waves are associated with the fundamental mode. Also, in this case, the existence of low velocity zones in the crust is not required. Lg, Rg propagate in structures with and without a low velocity channel in the upper mantle.