Kent earthquake: why does Britain have so few quakes?

Kent was shaken, gently, by a 4.2 magnitude earthquake this morning, with shockwaves spreading out from Sandwich to Canterbury, Margate and Southend-on-Sea in Essex.

Some residents of the surrounding area said that they thought that a plane had crashed or a bomb had gone off, the BBC reports. The epicentre of the quake, which struck at 2.52am, was about ten miles underground.

Seismic activity is not unusual in Britain, but it is rarely serious – particularly in comparison with earthquakes elsewhere in the world, such as the two that shook Nepal in recent weeks.

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How often does the UK have earthquakes?

Britain is not generally thought of as a country affected by earthquakes, but 20 to 30 tremors are felt by UK residents each year. Nevertheless, they are rarely very strong and most cause no damage.

What was Britain's worst earthquake?

According to the British Geological Survey, Britain's worst recorded earthquake struck the Dogger Bank in 1931. The quake had a magnitude of 6.1, but because it was centred 60 miles offshore it caused only minor damage to buildings along the east coast of England.

The most damaging recorded earthquake took place 47 years earlier when an earthquake hit Colchester, cracking walls and toppling chimney stacks.

How often do they occur?

While magnitude 4 earthquakes occur only every two years or so, and magnitude 5 quakes every 10 to 20 years, scientists believe that a 6.5 magnitude quake is technically possible.

Christchurch in New Zealand was shaken by a slightly less powerful magnitude 6.3 quake in 2011, leaving 185 people dead and at least 1,500 people injured. Rebuilding the city cost the country £20.3bn – almost 20 per cent of New Zealand's annual GDP, The Guardian says.

Why do earthquakes happen in the UK?

Britain is affected by earthquakes due to its "turbulent geological past", the British Geological Survey says. In the UK, the causes of most earthquakes are not always clear, but they include "regional compression caused by motion of the Earth's tectonic plates, and uplift resulting from the melting of the ice sheets that covered many parts of Britain thousands of years ago", the BGS says.