Vertical and SV components of Sa

The vertical and SV components of Sa are identified with stationary phases of higher-mode Rayleigh waves for realistic sources placed at depths greater than 60 km. This identification is valid both for continental structures containing a low-velocity channel in the upper mantle and those which do not contain such a channel The result for the SH component of Sa, which indicates that the energy associated with Sa behaves as though it were being transported by a single, homogeneous, low-velocity layer overlying the higher-velocity material below the ‘400 km-discontinuity’, also applies to the vertical and SV components of these waves.