Wednesday 29 May 2013

Magnitude 3.8 Earthquake off the Lleyn Peninsula, North Wales.

A magnitude 3.8 Earthquake at a depth of 8 km occurred off the coast of the Lleyn Peninsula in North Wales, slightly after 4.15 am British Summertime (slightly after 3.15 am GMT) on Wednesday 29 May 2013, according to the British Geological Survey. While this is not a large Earthquake and is unlikely to have caused any damage or injuries, it is exceptionally large for Wales, and was felt as far away as Southport in Lancashire, with many people on the Peninsula reporting being waken by the quake and hearing a loud rumbling noise that went on for about 30 seconds.

Map showing the location of the 29 May 2013 Earthquake, and places where people reported feeling the quake. British Geological Survey.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process. 

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.

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