Monday 30 April 2012

Earthquake in Snowdonia National Park, Friday 27 April 2012.

On Friday 27 April 2012 slightly after 5.35 am British Summer Time (slightly after 4.35 am GMT) an Earthquake occurred in the north of the Snowdonia National Park, about 2.5 km east of the village of Bethesda in Gwynedd, at a depth of about 3 km. This was recorded by the British Geological Survey as measuring 1.4 on the Richter Scale.

The location of the 27 April Quake. BGS.

A quake as small as this is unlikely to have been felt unless anyone was very close to it, and there is no realistic danger of any damage or casualties. This area of Wales, while a long way from any active plate margin, is not completely strange to seismic activity, and will suffer several quakes of this magnitude in a year, and a larger quake roughly once every three years. Occasionally these quakes cause minor damage and injuries, and the only Earthquake related casualty ever recorded in Wales happened in Gwynedd, in 1940, when an elderly woman fell down a flight of stairs during a quake measuring 4.7 on the Richter Scale.

The source of individual quakes is hard to determine, as the rocks of Wales are subject to tectonic stresses from a variety of forces. The whole of Eurasia is being pushed eastwards by the expansion of the Atlantic Ocean. At the same time western Eurasia is being pushed northward by the impact of Africa. There is also expansion going on to a lesser extent under the North Sea, the Bay of Biscay and the Rhine Valley, all of which exert pressure on British rocks. In addition Britain is still subject to glacial rebound; the north of the country was covered by hundreds of meters of ice as recently as 10 000 years ago, pushing the lithosphere down into the underlying mantle. Since the ice melted the whole island has been slowly rebounding, exerting more stress on the rocks at the surface.

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