The British Geological Survey recorded a Magnitude 1.3 Earthquake at a depth of about 7 km, roughly 1 km off the south coast of the Isle of Arran slightly after 11.50 am British Summertime (slightly after 10.50 am GMT) on Monday 12 August 2013. This is a small quake, and it is unlikely to have been felt on land, much less have caused any damage.
The approximate location of the 12 August 2013 Arran Earthquake. Google Maps.
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.
See also Earthquake on the Rinns of Islay, Earthquake on the Morvern Peninsula, Earthquake beneath Loch Maree, Earthquake on the Isle of Jura and Small Earthquake on the Isle of Mull.
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