Saturday, 13 October 2012

Two Earthquakes beneath the English Channel.

On Thursday 11 October 2012, slightly after 1.30 pm, British Summertime (slightly after 12.30 pm, GMT), the British Geological Survey recorded a Magnitude 2.3 Earthquake 14 km beneath the English Channel, roughly 40 km north of Caen and 40 km west of Le Havre. This was followed after slightly under two hours by a second quake of a similar magnitude, slightly to the northwest and 2 km deeper. Neither of these quakes is likely to have caused any damage or casualties, and may not actually have been felt by anyone; they were too small, too deep and too far offshore to cause any problems.

The location of the 11 October 2012 Earthquakes. Google Maps.

These are the second and third quakes beneath the Channel this week, a quake took place on Monday 8 October, to the west of the Cherbourg Peninsula, though that was probably unrelated given the distance. The 11 October quakes, however, were almost certainly connected in origin.

The precise causes of quakes beneath the Channel can be hard to determine, as the area is subjected to tectonic stresses from a variety of different sources, and most quakes are probably the result of a combination of these. The Channel area is (along with the rest of Eurasia) being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Eurasia from the south. It is also subjected to stresses caused by lesser expansion centers beneath the North Sea, the Rhine Valley and the Bay of Biscay. The area is also effected by tectonic stresses caused by glacial rebound; until about 10 000 years ago much of the north of Europe, including northern parts of the UK and upland areas of France, was covered by a thick layer of glacial ice. This pushed the rocks of the European lithosphere down into the underlying mantle. The ice has now gone and the rocks are now springing back into place (at geological speeds), causing occasional Earthquakes in the process.


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