Rayleigh wave

5.20  Rayleigh wave. Surface wave associated with the free boundary of a solid, such that a surface particle describes an ellipse for which the major axis is normal to the surface and the center is at the undisturbed surface. At maximum particle displacement away from the solid surface, the motion of the particle is opposite to that of the wave.

Annotation              The propagation velocity of a Rayleigh wave is slightly less than that of a shear wave in the solid; the wave amplitude of the Rayleigh wave diminishes exponentially with depth into the solid.