Earthquakes in the UK: Why do they happen, how often do they happen, when was the largest and how does it compare with the rest of the world?

 
Catherine Neilan
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Ramsgate earthquake: Hundreds of people have reported feeling tremors last night (Source: BGS)
Last night hundreds of people in Kent were woken by a 4.2 magnitude earthquake, which occurred just before 3am.
This is the second-biggest earthquake in nearly a decade: back in 2007, Folkestone was rocked by tremors measuring 4.7 magnitude.
The UK is not known for being a hive of tectonic activity, but according to the British Geological Survey, people report between 20 and 30 earthquakes each year, while "a few hundred" smaller ones are recorded by sensitive instruments.

When was the biggest earthquake to hit Britain?

The largest earthquake registered as occurring in Britain actually took place in the North Sea – near a large sandbank called Dogger Bank – in 1931.
Although it was 60 miles offshore, the 6.1 magnitude earthquake was still powerful enough to cause some damage to buildings on the coast of England.
However, the most damaging earthquake in Britain occurred near Colchester in 1884, affecting around 1,200 buildings after chimneys collapsed and walls were cracked.

Where do most of the UK's earthquakes occur?

Most earthquakes appear on the west coast of the country, and the North Sea is more active than the mainland..
They almost never occur in eastern Scotland and the north east of England. Ireland is also "almost completely free" from earthquakes.

Historical seismicity of the UK from 1832 to 1970 - yellow represents magnitude higher than three, red represents those between two and three (Source: BGS)

How often does the UK experience significant earthquakes?

Not very. A magnitude four earthquake happens in Britain roughly every two years, and larger ones occur every 10-20 years.

Why do we get earthquakes in Britain?

According to the BGS it's "unclear" what causes the earthquake activity in the UK, although there is regional compression caused by the motion of the Earth's tectonic plates as well as uplift caused by the melting of the ice sheets that covered many parts of the country thousansds of years ago.

How do UK earthquakes compare to those in the rest of the world?

Research suggests the largest earthquake possible in the UK is around a magnitude of 6.5.
To put that into perspective, Nepal's devastating earthquake on April 25 was 7.8; its second earthquake earlier this month was registered at 7.3.
The biggest earthquake on record occurred in Valdivia, Chile, in 1960. That was a magnitude of 9.5. The quake that caused the Indian Ocean tsunami in 2004 was 9.2.

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