What is an earthquake?

An earthquake is a sudden, violent, shaking of the ground caused by the sudden release of energy in the Earth’s lithosphere that creates seismic waves. Earthquakes range in size from those that are so weak they cannot be felt to those that are so violent they destroy cities.

The word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused by:

• movement at tectonic faults;
• volcanic activity;
• landslides;
• mine blasts; and
• nuclear tests

The point where an earthquake starts is known as its focus (or hypocentre). The point on the surface of the Earth, directly above the focus is called the epicentre.

An earthquake’s power is measured on the Richter scale using an instrument called a ‘seismometer’.

The effects of an earthquake can be devastating; they can destroy settlements, change landscapes and cause many deaths.