Wednesday 10 October 2012

Earthquake under the English Channel.

On Monday 8 August 2012, slightly after 4.10 am, British Summertime (slightly after 3.10 am, GMT), the British Geological Survey recorded a Magnitude 2.2 Earthquake 7 km beneath the English Channel, roughly 30 km northwest of Guernsey. An Earthquake this small and this far offshore is highly unlikely to have been felt, much less to have caused any damage or casualties.

Map showing the location of the 8 August Earthquake. Google Maps.

The cause of quakes in the Channel area is not always immediately obvious. Events at the seabed surface are most likely to be submarine landslips, but this event is far too deep for this to be a possibility. The Channel is on the Eurasian Plate, and 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, though neither of these are immediate causes of stress. Closer to the Channel there are lesser areas of extension beneath the North Sea, the Rhine Valley and the Bay of Biscay, all of which excerpt tectonic stress on the Channel area to some extent. Finally there is glacial uplift; much of Europe was covered by a thick layer of glacial ice until about 10 000 years ago, including most of the north of the UK, and upland areas of France, such as the Alps and the Pyrenees. This ice pushed the rocks of the lithosphere down into the underlying mantle, and now that it is gone these rocks are springing back up, albeit at geological speeds, causing the occasional Earthquake in the process.

Witness accounts are a valuable resource for scientists trying to understand Earthquakes and the rock processes that cause them. If you felt this quake (or if you were in the area but did not feel the quake, which is also useful information) you can report it to the BGS here.

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