Slightly before 6.40 am British Summertime (slightly before 5.40 am GMT) on Sunday 25 August 2013, a Magnitude 2.4 Earthquake at a depth of 5 km occurred beneath the Irish Sea, roughly 25 km off the Lancashire Coast, according to the British Geological Survey. This was followed by a second quake slightly before 11.00 am British Summertime (slightly before 10.00 am GMT), this time with a Magnitude of 3.2 at a depth of 8 km, and roughly 1 km to the southwest of the original tremor. These are quite large events for the UK, although unlikely to cause any problems this far offshore. Both quakes were felt in the Fleetwood and Barrow-in-Furness areas.
The approximate locations of the 25 August 2013 Irish Sea Earthquakes. 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 and England being more prone to quakes than the rest of the countries.
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 either of these quakes, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here (first quake) or here (second quake).
See also Magnitude 1.3 Earthquake of the Isle of the Isle of Arran, Magnitude 2.1 Earthquake in Cheshire, England, Magnitude 1.2 Earthquake in the Peak District, Derbyshire, Magnitude 3.8 Earthquake off the Lleyn Peninsula, North Wales and Earthquake in Shropshire.
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