What is an earthquake?

Crustal Stress

Earthquake Waves Spread Out

Movements within the Earth’s crust cause stress to build up at points of weakness and rocks to deform.

Stored energy builds up in the same way as energy builds up in the spring of a watch when it is wound.

When the stress finally exceeds the strength of the rock, the rock fractures along a fault, often at a zone of existing weakness within the rock. The stored energy that is suddenly released as an earthquake!

Intense vibrations, or seismic waves, spread out from the initial point of rupture, the focus, like ripples on a pond. These waves are what makes the ground shake and can travel large distances in all directions.

Near the focus, the waves can be very large, making them extremely destructive.

Bent ruler.

Related topics

Punishing a catfishEarthquakes: myths and legends

In ancient times earthquakes were thought to be caused by restless gods or giant creatures slumbering beneath the Earth.

Historical seismicity of the UK (yellow) from 1832 to 1970 for earthquakes of magnitude above 3.0 and instrumental seismicity (red) from 1970 to present for earthquakes with ML >2.0. Earthquakes in the UK

Despite being nowhere near a plate tectonic boundary the UK experiences hundreds of small earthquakes each year.

UK earthquake timeline UK earthquake timeline

An interactive map of UK earthquakes

Major world earthquakes map Major world earthquakes map

An interactive map of the biggest and the deadliest earthquakes in the world

Classroom activities

What is an earthquake? Movement of faults and boundaries using foam blocks

Using pieces of foam or card you can model the movement of tectonic plates in different kinds of faults and boundaries.