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Experts have revealed what caused the earthquake which sent tremors across the city.

Earlier on Saturday afternoon there was a magnitude 4.4 earthquake in South Wales, about 12 miles/20 kilometres off Swansea.

The earthquake was felt across much of the country, including in Plymouth.

This included Aaron Baker, who was at home in Stoke at the time.

He said: "I was watching football on the sofa and my building began to shake and then the sofa began to move and I nearly fell off."

(Image: EMSC)

Richard Luckett, a seismologist at the British Geological Survey said this is the largest earthquake in mainland UK since 2008.

He told The Herald: "There has been a magnitude 4.4 earthquake in South Wales, about 20 km NNE of Swansea.

"This earthquake has been felt across a large area of Wales and England, with the furthest reports so far from Birmingham and Devon.

"This is the largest earthquake in mainland UK since the 5.2 magnitude Market Rasen earthquake in 2008."

Swansea University was evacuated and people ran into the streets in fear, as the tremor was compared to everything from a "massive explosion" to a car crash, reports the Mirror Online.

What is an earthquake?

Movements within the Earth’s crust cause stress to build up at points of weakness and rocks to deform, says Geological Survey.

Stored energy builds up in the same way as energy builds up in the spring of a watch when it is wound.

When the stress finally exceeds the strength of the rock, the rock fractures along a fault, often at a zone of existing weakness within the rock. The stored energy that is suddenly released as an earthquake!

Intense vibrations, or seismic waves, spread out from the initial point of rupture, the focus, like ripples on a pond. These waves are what makes the ground shake and can travel large distances in all directions.

Near the focus, the waves can be very large, making them extremely destructive.

What is the British Geological Survey?

The British Geological Survey is a world-leading geological survey. It focuses on public-good science for government, and research to understand earth and environmental processes.



As a public sector organisation BGS is responsible for advising the UK government on all aspects of geoscience as well as providing impartial geological advice to industry, academia and the public.

The BGS is part of the Natural Environment Research Council (NERC), which is the UK's main agency for funding and managing research, training, and knowledge exchange in the environmental sciences. The NERC reports to the UK government's Department for Business, Innovation and Skills (BIS).

It also undertake an extensive programme of overseas research, surveying and monitoring, including major institutional strengthening programmes in the developing world.