Monday 14 May 2012

Earthquake in Carmarthenshire.

On Friday 11 May slightly after 7.15 pm British Summer Time (slightly after 6.15 pm GMT), an Earthquake occurred about 10 km west of Carmarthen in South Wales, according to the British Geological Survey, which recorded the quake as occurring at a depth of 5 km and as measuring 1.8 on the Richter Scale. Such a small quake is unlikely to have caused any damage or injuries, and may not have been felt by anyone.

The location of the 11 May Earthquake. BGS.

Although Wales is located far from any active tectonic boundaries, it still suffers the occasional Earthquake, though these tend to be commonest in the northwest (a good rule of thumb for the UK in general), and are quite rare in Carmarthenshire. The county has suffered three quakes of note in recorded history. The most recent of these was in November 1893, when a quake estimated to have measured 5.0 on the Richter Scale (neither the scale itself nor any method of measuring shake intensity had been invented in 1893) was felt as far away as Lancaster and London, and caused minor damage as far away as Shropshire; though no major damage was caused anywhere and there were no recorded casualties. Earlier than this Carmarthenshire suffered a quake in October 1802 estimated to have measured 3.3 on the Richter Scale, and a quake in August 1690 estimated at 4.7 on the Richter Scale. Again there is no record of any notable damage or injuries from either of these quakes.

The causes of Earthquakes in the UK are complex, as the country is subjected to tectonic stresses from a number of sources. The Atlantic Ocean is spreading at about 25 mm a year, pushing Eurasia to the east. At the same time Africa is moving northward at about 21.5 a year, pushing into Europe from the south, causing uplift in the south and quakes across the continent (though less often in the north). There is also spreading to a lesser extent beneath the North Sea, the Bay of Biscay and the Rhine Valley, all of which excerpt some stress on rocks of the UK. Finally their is glacial rebound; the north of Britain was covered by thick ice till about 10 000 years ago, pushing the surface downward into the underlying mantle. This is now springing back upwards, at geological speeds.

The British Geological Survey are interested in hearing from anyone who felt this quake, or who was in the area but did not feel it (which is also data). You can contact them here.

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