On Saturday 29 December 2012, at 10.30 pm GMT, the British Geological Survey recorded a Magnitude 1.4 Earthquake at a depth of 14 km beneath southwest Herefordshire, roughly 15 km southwest of Hereford and 20 km west of Ross-on-Wye. This is far too small and too deep to have caused any damage or injuries, and may not have been felt at the surface at all.
The location of the 29 December 2012 Earthquake. Google Maps.
There is no overridingly obvious cause for most Earthquakes in the UK; the country is subject to tectonic pressures from a number of sources, and most quakes are thought to be a combination of more than one of these. Britain is being pushed to the east by the expansion of the Atlantic Ocean (along with the rest of Eurasia) and to the north by the impact of the African Plate into Europe from the south. There are also lesser areas of geological expansion beneath the North Sea, the Rhine Valley and the Bay of Biscay, all of which exert some pressure on UK rocks. Finally there is glacial rebound; until about 10 000 years ago much of the north of the UK was covered by a thick layer of glacial ice, which pushed the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are slowly springing back into place, causing the occasional Earthquake in the process, though this is more of an issue further to the north, particularly on the west coast of Scotland, the most quake-prone part of the country.
Witness reports can be important in helping geologists to understand the processes going on in Earthquakes. If you felt this quake (or were in the area but didn't, which is also useful information) you can report it to the British Geological Survey here.
See also Earthquake in Leicestershire, Earthquake off the Dorset Coast, Earthquake in Carmarthenshire, The Portsmouth Earthquake of 14 July 2011 and Earthquakes on Sciency Thoughts YouTube.
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