Friday 22 May 2015

Magnitude 4.2 Earthquake off the coast of Sandwich Bay, Kent.

The British Geological Survey recorded a Magnitude 4.2 Earthquake at a depth of 13 km off the coast of Sandwich Bay, Kent, in the southeast of England slightly after 2.50 am British Summertime (slightly after 1.50 am GMT) on Monday 11 May 2015. There are no reports of any injuries associated with this event, though there are unconfirmed reports of houses being damaged in the village off Flete, to the north of the epicenter of the quake, and people have reported feeling the event across all of Kent and as far away as Oxfordshire and Norfolk.

Map showing the epicenter of the 22 May 2015 East Kent Earthquake, and the areas where it was felt. BGS.

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. However, while quakes in southern England are less frequent, they are often larger than events in the north, as tectonic presures tend to build up for longer periods of time between events, so that when they occur more pressure is released.

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.

(Top) Simplified diagram showing principle of glacial rebound. Wikipedia. (Bottom) Map showing the rate of glacial rebound in various parts of the UK. Note that some parts of England and Wales show negative values, these areas are being pushed down slightly by uplift in Scotland, as the entire landmass is quite rigid and acts a bit like a see-saw. Climate North East.

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.

See also...

The British Geological Survey recorded a Magnitude 1.9 Earthquake at a depth of 6 km slightly to the northeast of the village of North Fambridge in Essex...

Homes evacuated after sinkhole opens up in Swanley, southeast England.
Two homes have been evacuated in the town of Swanley in Kent, southeast England after a sinkhole opened up on Thursday 26 March 2015 swallowing...

Second Hampshire Earthquake in three days.
The British Geological Survey recorded a Magnitude 1.8 Earthquake at a depth of 4 km, roughly 3 km to the northeast of Winchester in Hampshire, England, at about 4.25 pm GMT on...

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