Rayleigh waves are surface waves with particle motion that is

• A. Straight-line Motion Parallel to the Surface
• B. Circular Motion at Depth
• C. Elliptical Motion Near the Surface
• D. Purely Longitudinal Motion

Answer: (C)

Rayleigh waves produce particle motion that is elliptical in the vertical plane of propagation right at the surface. This comes from how these surface waves combine vertical and horizontal ground motions as the wave travels, so a particle traces an ellipse rather than moving in a straight line or purely along one direction. The motion is strongest near the surface and decays with depth, so you don’t get circular motion deeper down. That’s why the characteristic description is elliptical motion near the surface. The other descriptions—straight-line motion parallel to the surface, purely longitudinal motion, or circular motion at depth—don’t match how Rayleigh waves actually move the ground.