Seismic waves

Seismic waves can be caused by the sudden breaking of rock within the earth, an explosion, or potentially any other phenomenon that makes the ground vibrate. Seismic waves caused by an earthquake are the result of the sudden release of energy in the Earth's lithosphere. They travel through the earth and are recorded on seismographs. Typically they come in pairs consisting of P (primary) and S (secondary) waves. P-waves are longitudinal waves. They are the fastest kind of seismic waves, and, consequently, the first to 'arrive' at a seismic station. S-waves, on the other hand, are transverse waves and they propagate more slowly than the P-waves. They are therefore the second type of disturbance recorded on a seismogram during an earthquake. The difference in the arrival time between the P and S-waves represents the distance of the seismic station to the epicenter of the earthquake.