Question: seismic waves which travel only through the outer layer of the earth are called
Answer: 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 ) .