Structure of the Earth
The Earth is made up of different layers:
- the core at the centre, which is mainly metal
- the mantle, which is mainly rock
- the crust, which is the part we can see
The crust (together with the upper layer of the mantle) is made up of different pieces, called plates. These plates fit together like a jigsaw and are moving at a rate of a few centimetres a year, in different directions and at different speeds.
Some plates slide past each other, others move away from each other and some bump into each other. Sometimes these plates lock together when they meet. This is called a plate boundary or a fault line.
What are earthquakes?
As plates carry on moving in different directions over long periods of time, friction causes energy to build up. Eventually it becomes so great that the energy is released, which creates a shock wave - an earthquake. If the earthquake is beneath the ocean it can create a series of huge waves, called a tsunami.
There are thousands of earthquakes across the world each day and some are so small that they can only be detected by specialist equipment. Others can be so intense that they can create lots of damage and destroy towns and cities. The Richter magnitude scale is used to measure the size of earthquakes.
Many earthquakes occur around the Pacific Ocean. People who live there, in countries such as Japan, are used to earthquakes happening and build earthquake-resistant buildings that sway with the shock waves rather than fall down.
Although there are earthquakes in the UK, they are rare and so small that most people do not feel them.