People have searched for an answer to why earthquakes occur. After all, how can what seems like the whole world be moving?? Different civilizations have explained it in different ways. Native americans have thought that a large turtle carried the world on its back, and whenever it moved, the earth shook.

We think that earthquakes are caused by seismic waves. These can be caused by the rubbing of tectonic plates (the plates that the continents and oceans are on, floating on magma) But can also be in other places.

There are two classes of seismic (movement of the earth) waves, the Love and Rayleigh waves; and the P and S waves. The Love and Rayleigh waves move along the surface, and the P and S waves are from inside the earth.

	P stands for primairy waves, and move very quickly through the earth. P waves act as sound waves do, with vibration and everything is enlarged and shrunk.
S stands for secondairy waves, and only move through solid material (no water or liquid rock) and moves slower. It also moves in a wave like form:

When the P waves hit any point on the surface, that point is known as the epicenter, because it is the first part of the earthquake that touches the ground.

The love and Rayleigh waves are the source of most of the deadly vibration during the earthquake, the P waves kindof guide them to the epicenter, from which they diseperse, spreading like spiderwebs outwards..

More information about what an earthquake is can be found [here]

Information about major past earthquakes can be found [here]

Earthquake links can be found [here]

More earthquake pictures can be found [here]

Information on how earthquakes are classified can be found [here]