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The structure of the Earth

A cartoon globe cut open to show the core, crust and mantle.

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
A cartoon globe cut open to show the core, crust and mantle.
A cartoon globe with tectonic plates on its surface.

The crust (together with the upper layer of the mantle) is made up of different pieces, called tectonic 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.

Arrows on tectonic plates pointing towards each other.

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.

Arrows on tectonic plates pointing towards each other.
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What happens during an earthquake?

A diagram of two tectonic plates sliding against each other.
  • As plates move in different directions over long periods of time, friction causes energy to build up.

  • It becomes so great that the energy is released, which creates a shock wave - an earthquake.

A diagram of two tectonic plates sliding against each other.
  • If an 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.

Tsunami and earthquake destruction in Japan in 2011.
Image caption,
Tsunami and earthquake destruction in Japan in 2011.
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Watch: How do earthquakes work?

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Earthquake scale and impacts

A seismograph.
Image caption,
A seismograph measures the strength of earthquakes.
  • Some earthquakes are so small that they can only be detected by specialist equipment. Others can be so intense that they can destroy towns and cities.

  • The Richter magnitude scale is used to measure the size of earthquakes. The higher the number, the more powerful the earthquake and the higher the chance that it will cause real damage.

  • The largest earthquake recorded in the UK happened in 1931, in the North Sea, and measured 6.1 on the Richter scale.

A seismograph.
Image caption,
A seismograph measures the strength of earthquakes.
Number on Richter scaleHow many happen in the world per year?What does it mean?
2.5 or lessMillions each yearUsually not felt, but some can be recorded by scientists
2.5 to 5.4500,000 per yearOften felt, but only causes minor damage
5.5 to 6.01,000 per yearCan cause slight damage to buildings and other structures
6.1 to 6.9100 per yearMay cause a lot of damage in very populated areas
7.0 to 7.910-15 per yearMajor earthquake and serious damage caused
8.0 or greaterOnce every year or twoThis is a very large earthquake which can totally destroy large areas

Source: USGHS/Modified Mercalli Intensity

A cartoon of people on computers and machines looking at the Earth.
  • 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.

A cartoon of people on computers and machines looking at the Earth.
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Activity: Quiz 鈥 Earthquakes

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