Earthquake Scotland 2021: what caused 3.1 magnitude tremor felt in Glasgow, Argyll and Edinburgh?

Residents of western Scotland received a bump in the night after an earthquake shook the region in the early hours of Tuesday.

A quake with a magnitude of 3.1 occurred just before 2am with its epicentre some 11 miles north-west of the town of Lochgilphead, 88 miles north-west of Glasgow, according to the United States Geological Survey (USGS).

Over 30 people reported to the USGS that they had felt the tremor, with reports coming from as far as Edinburgh and even Ballycastle in Northern Ireland.

The agency said the quake happened 10km (six miles) below the Earth’s surface.

What causes an earthquake?

Earthquakes are caused by sudden movements along the faults found within the Earth.

The British Geological Survey (BGS) says that this movement “releases stored-up ‘elastic strain’ energy in the form of seismic waves, which propagate through the earth and cause the ground surface to shake”.

The earth’s tectonic plates are always slowly moving around, but their edges can get stuck due to friction - when the stress built up on the edge overcomes the friction, an earthquake occurs.

How often does the UK have an earthquake?

Data from the BGS shows between 200 and 300 earthquakes are detected in the UK every year, with tremors of between 3.0 and 3.9 magnitude occurring on the mainland once every three years on average.

The BGS says that “between 20 to 30 earthquakes are felt by people each year and a few hundred smaller ones are only recorded by sensitive instruments”.

Most earthquakes recorded in the UK are small and cause little to no damage.

The biggest earthquake to have been recorded in the UK was on 7 June 1931, where an earthquake with a magnitude of 6.1 occurred near the Dogger Bank.

Despite being 60 miles offshore, it was still felt across most of Britain.

The earthquake that caused the most damage in the UK was that of an earthquake in the Colchester area in 1884, which left around 1200 buildings in need of repairs.

According to a map of earthquake activity in the British Isles, most earthquakes occur on the western side of the British mainland, and are generally absent from eastern Scotland and north-east England.

Additionally, Ireland is “almost completely free of earthquakes” the BGS says.

What is the biggest earthquake ever recorded?

According to the USGS, the biggest earthquake ever recorded happened in 1960, and is known as the Valdivia earthquake or Great Chilean earthquake, and occurred in Bio-Bio, Chile.

It had a magnitude of 9.5 and lasted approximately 10 minutes when it happened at around 3:11pm local time.

Tsunamis were caused by the tremor which severely affected the Chilean coast, causing waves of up to 25 metres (or 82 ft).

It’s unclear how many died as a result of the earthquake, with various estimates ranging from 1,000 to 6,000.

The top five biggest recorded earthquakes are:

• Valdivia Earthquake in Bio-Bio, Chile, with a magnitude of 9.5 in 1960
• Great Alaskan Earthquake in Southern Alaska, with a magnitude of 9.2 in 1964
• Sumatra-Andaman Islands Earthquake off the west coast of Northern Sumatra, with a magnitude of 9.1 in 2004 
• Tohoku Earthquake in near the east coast of Honshu, Japan, with a magnitude of 9.1 in 2011
• Kamchatka Earthquake off the east coast of the Kamchatka Peninsula, Russia, with a magnitude of 9.0 in 1952