Waves represent the movement of energy through a medium, with no net movement of the material that makes up the medium.

Surface Waves

Ocean waves are a type of surface wave (known as a Rayleigh wave) and the energy they transmit usually comes from winds blowing across the surface of the water. Particles of water move in more-or-less circular orbitals, and the motion diminishes with distance from the surface. As a general rule, motion ceases at a depth equal to one half of the wavelength:

The rolling waves we experience during earthquakes are Rayleigh waves, exactly analogous to ocean waves. They travel at the Earth's surface (or at the boundary between the ground and the atmosphere), and their motion diminishes with depth from the surface.

Body Waves

Some waves are not restricted to the surface of a medium but can travel through its interior. Examples of these include acoustic waves (sound waves) and light waves. These are known as body waves and they fall into two categories:

Pressure waves (also known as P-waves or primary waves) are marked by the oscillation of particles in the same direction as wave motion.

Shear waves (aka S-waves or secondary waves) are marked by the oscillation of particles at right angles to wave motion.

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