Thursday 27 June 2013

Series of Earthquakes off the Lleyn Peninsula, northwest Wales.

A series of three minor Earthquakes happened roughly 2 km off the northeast coast of the Lleyn Peninsula in northwest Wales on the evening of Wednesday 26 June 2013, according to the British Geological Survey. The quakes took place over a period of about two and a half minutes at about 11.30 British Summertime (10.30 GMT) . The quakes ranged in Magnitude from 1.2 to 2.8, and occurred at depths of between 2 and 8 km. There are no reports of any damage or casualties. but the quakes were apparently felt across much of the peninsula as well as on Anglesey and as far away as Barmouth and Rhyl.

Map showing the locations of the 26 April Earthquakes, and areas where people have reported feeling them. British Geological Survey.

As a rule of thumb 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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