Thursday 6 September 2012

Second Earthquake beneath Cheshire.

On Wednesday 5 September 2012, slightly before 5.10 pm British Summertime (slightly before 4.10 pm GMT) the British Geological Survey recorded a Magnitude 1.1 Earthquake roughly 5 km southwest of the Cheshire Town of Congleton, at a depth of 11 km. An Earthquake this small is unlikely to have caused any damage or injuries, and may not have been noticed by anybody, or recognized as an Earthquake if it was. 

Map showing the location of the 5 September Earthquake. BGS.

As a rule of thumb Earthquakes become more common in the UK as you travel north and west, making Cheshire one of England's more Earthquake prone counties. This is the second Earthquake in Cheshire in three days, and the two events are likely to be related, though it is by no means certain we will ever know the precise cause of either event. Britain is not close to any active plate margins that would provide an simple explanation for any Earthquakes, but instead is subject to tectonic stresses from a number of different sources, with most quakes probably being a result of a combination of more than one of these.

Britain (along with the rest of Europe) is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into southern Europe in the Mediterranean region. Britain is also subject to stresses caused by smaller areas of expansion beneath the North Sea, the Rhine Valley and the Bay of Biscay. The country is also suffering the effects of glacial rebound; until about 10 000 years ago much of the north of the country was covered by a layer of ice hundreds of meters thick, pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, removing the pressure, and the rocks are still springing back into position, causing the occasional Earthquake as they do so.

Geologists can use witness statements to try to understand Earthquakes and the processes that lead to 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 BGS here

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