Earthquakes

FAQs

What is an earthquake?

An earthquake is a sudden release of energy in the crust of the Earth that creates seismic waves, like shock waves. Depending on the size of the earthquake, these waves can cause great damage to buildings.

The centre of the earthquake beneath the surface is called the hypocentre. The location on the earth’s surface is known as the earthquake’s epicentre.

What causes earthquakes?

The outer shell of the Earth, the lithosphere, is covered by rigid plates called tectonic plates. These are constantly on the move driven by forces deep within the Earth.

Their movement causes stress to build up at points of weakness in the rock called ‘faults’. When the stress becomes too great the rocks fracture along the fault releasing energy in the form of an earthquake.

Seismic waves spread out from the point of fracture like ripples in a pond.

What are seismic waves?

Seismic waves are caused by the release of energy as a fault moves. These are felt as intense vibrations and the ground shakes.

Most of what we know about the Earth’s interior comes from studying seismic waves.

Their speed depends on the density of the rock they are moving through, so we can find out about the changes in the Earth’s density at different depths by studying the speed of the waves.

They show that the Earth is made up of 3 layers, called the crust, the mantle and the core.

Where do earthquakes happen?

They can happen anywhere, but most earthquakes occur at the boundaries between tectonic plates where they are pushed together, pulled apart or slide past one another.

The most famous plate boundaries are the ‘ring of fire’ that encircles the Pacific Ocean.

How big can an earthquake get?

The magnitude of an earthquake is calculated using the Richter scale. This measures the amount of seismic energy released by the quake.

The Richter scale is logarithmic. This means that a magnitude 5.0 earthquake is ten times more powerful than a magnitude 4.0.

The largest earthquake ever recorded occurred in Chile in 1960. It measured 9.5 on the Richter scale.

The Indian Ocean earthquake of 2004 had a magnitude of 9.0. It caused a tsunami that killed over 227,000 people. Scientists think that an earthquake of magnitude 10 or larger is very unlikely.

Can we predict them?

No. We know that most earthquakes occur at plate boundaries but at the moment we can’t predict exactly when one will occur and how big it will be.

What does an earthquake feel like?

It depends on how large it is and how far away from the earthquake’s epicentre you are.

A big earthquake close by will feel like a sudden large jolt followed by violent shaking that can last for up to 2 minutes.

A small, faraway quake isn’t easy to feel at all, but if you are sitting down and you keep still then you may feel a couple of gentle shakes.

Do earthquakes happen in the UK?

Yes. Although nowhere near as devastating as those that take place in other parts of the world, the UK experiences a few hundred earthquakes per year. Most are so small that they can only be detected using sensitive equipment.

The UK’s most destructive earthquake occurred in Colchester in 1884. It left over 1,000 buildings damaged.