Earthquakes

Earthquake

By Royal Society University Research Fellow Dr Richard Walker
Department of Earth Sciences, University of Oxford

How do earthquakes occur?

Earthquakes happen on planes of weakness in the Earth, called faults, where one body of rock is able to move past another. Although many earthquakes occur on land, the largest, such as the one that caused the 2004 Boxing Day tsunami, occur along the edges of oceanic plates.

Can we predict earthquakes?

Sadly, despite a lot of effort, the prediction of earthquakes is still beyond our reach: we may never be able to say that an earthquake will occur at a specific place and time. But we are getting much better at identifying areas that are at risk from earthquakes and at saying how often, on average, earthquakes occur in these regions. This kind of information, along with education and the enforcement of effective building codes, helps in planning and preparing for the future.

What was the largest ever earthquake?

The largest known earthquake, with a magnitude of 9.5, occurred on the Chile subduction zone in 1960. But the most destructive earthquake (magnitude 8), which killed over 820,000 people, was the 1556 Shaanxi earthquake in central China. With increasing populations and rapid growth of cities in earthquake-prone parts of the world the human cost of earthquake disasters is likely to rise.

How is the size of an earthquake measured?

Magnitude is the traditional measurement of an earthquake’s size; for each magnitude increase of 1, the earthquake releases about thirty times more energy. The largest UK earthquake of recent years was in Lincolnshire in 2008 and had a magnitude of 4.8. This earthquake was actually about 2,000 times smaller in terms of energy release than the recent destructive earthquake in Haiti (magnitude 7).