Earthquakes are caused by the movement of the Earth’s tectonic plates. Earthquakes occur where the earth’s plates meet along plate boundaries (see plate tectonics page for more information on this). For example as two plates move towards each other, one can be pushed down under the other one into the mantle. If this plate gets stuck it causes a lot of pressure on surrounding rocks. When this pressure is released it produces shock waves. These are called seismic waves. This is an earthquake.
Cross section of an earthquake
The waves of energy spread out from the point where the earthquake started – the focus. More damage is done near the focus. The point on the earth’s surface directly above the focus is the epicentre.