Sciency Thoughts: Carmaerthenshire

Monday, 23 September 2013

Magnitude 1.4 Earthquake in Carmarthenshire, South Wales.

The British Geological Survey recorded a Magnitude 1.4 Earthquake at a depth of 2 km in Carmarthenshire, South Wales, roughly 10 km to the south of Carmerhen, slightly after 0.05 am British Summertime on Monday 23 September 2013 (slightly after 11.05 pm on Sunday 22 September GMT). This is a small quake, and highly unlikely to have caused any damage or injuries, although it may have been felt locally.

The approximate location of the 23 September 2013 Carmarthenshire 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.

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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.