This Demonstration shows the propagation of elastic waves, commonly known as seismic waves. Two types of seismic waves are shown here: pressure waves (P-waves) and shear waves (S-waves). The P-wave is longitudinal, and so oscillates along the direction of the wave propagation, while the S-wave shakes perpendicular to the travel direction.
By combining these two types, you can simulate other types, such as Rayleigh waves. In such cases, the particles move in a circle or ellipse. The movement can be observed in detail by increasing the length of the trail.