What Are Seismic Waves
Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.
Types of Seismic Waves
There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water. Earthquakes radiate seismic energy as both body and surface waves.
Body Waves
Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. These waves are of a higher frequency than surface waves.
P Waves
The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to arrive. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air. Have you ever heard a big clap of thunder and heard the windows rattle at the same time? The windows rattle because the sound waves were pushing and pulling on the window glass much like P waves push and pull on rock. Sometimes people can only feel the bump and rattle of these waves. P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the 'direction of wave propagation'. Click here to see a P wave in action.
S Waves
The second type of body wave is the S wave or secondary wave, which is the second wave to occur in an earthquake and they are much slower and much more destructive than P-Waves. An S wave can only move through solid rock, and not through any liquid medium. S waves move rock particles up and down, or side-to-side perpendicular to the direction that the wave is traveling in. This means they make the earth vibrate perpendicularly to the direction of the wave travel. This wave causes damage due to its configuration. It causes buildings to be thrust upward from the ground then the ground drops out from under it as the wave travels by.
