24 August 2011 Last updated at 14:21

Why do earthquakes happen?

Although the ground we walk on seems solid, the Earth's surface is actually made up of huge pieces of flat rock called tectonic plates.

They float on top of a layer of softer, squidgy rock called the mantle.

The plates move very slowly, over millions of years, and where they come together is called a fault.

When the plates rub together, the movement forces waves of energy to come to the Earth's surface.

This causes tremors and shakes - and these are called earthquakes.

They can cause huge amounts of damage, particularly in cities and built-up areas, where buildings, roads and bridges can collapse.