GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Earthquake seismic waves. Artwork of a section through an earthquake showing the three different types of seismic wave produced. The waves radiate out from the focus (or hypocentre) of the earthquake (red dot). The epicentre is the point on the surface above this. The earthquake causes P waves (red), S waves (yellow) and surface waves (mauve). P waves are compression waves, moving through alternating regions of compression and rarefaction, like sound in air. S waves are transverse waves, in which the earth moves at right angles to the direction of the waves. Surface waves move like waves on the surface of water, and are usually responsible for most damage. The San Andreas fault in California, USA, is a fault like this one.
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