Four main types of seismic waves: P, S, Love and Raleigh. Love and Raleigh are confined to the surface of the Earth and do not provide information about the interior of the Earth. P- and S-waves are body waves and travel through the interior of the Earth.
P-waves involve the transmission of pulses of compression and dlation (expansion), in which the particles of the medium vibrate backwards and forwards in the direction the wave is travelling (propagating). P-waves are like sound waves and become audible when they reach the surface, producing rumbling sounds.
S-waves involve shear displacements, meaning that the motion of the particles in the medium is at right angles (perpendicular) to the direction of wave propagation. The motion can be vertical, horizontal, or a combination of the two, depending on the nature of the earthquake. S-waves are similar to the motion induced when a taut rope is shaken.