<P> Rayleigh waves , also called ground roll , are surface waves that travel as ripples with motions that are similar to those of waves on the surface of water ( note , however , that the associated particle motion at shallow depths is retrograde , and that the restoring force in Rayleigh and in other seismic waves is elastic , not gravitational as for water waves ) . The existence of these waves was predicted by John William Strutt , Lord Rayleigh , in 1885 . They are slower than body waves , roughly 90 % of the velocity of S waves for typical homogeneous elastic media . In the layered medium ( like the crust and upper mantle ) the velocity of the Rayleigh waves depends on their frequency and wavelength . See also Lamb waves . </P>
seismic waves which travel only through the outer layer of the earth are called
Rayleigh waves