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Seismic Events in London

Big Ben, London

Q: I want to enquire as to the likelihood of an upcoming earthquake. I have been led to believe that there is a major seismic event in London every 300 years. I have been told that the best course of action is to take cover under a table or door frame. Please advise me how I can prepare myself for such tectonic activity.

From Ms Tendayi Bloom (December 2009)

Reply by Dr Ted Nield

You can rest assured that major seismic events - likely to cause damage to buildings, injury or loss of life - are extremely unlikely in the UK as a whole and are not at all likely in London. Seismic activity close to London was most recently reported from Folkestone, Kent, in 2007.

Historically the people of Kent have felt earthquakes centred in, or near, the Dover Straits in 1950, 1776, 1580 and 1382; the two earliest ones had magnitudes estimated at just under 6, and caused damage as far as London, where in 1580 two people were killed by falling masonry. The last earthquake felt by residents in Folkestone was actually a Dutch earthquake (epicentre near Maastricht) in 1992. Comparisons can be made between the Folkestone event and the Colchester earthquake of 1884, magnitude 4.6 ML. At Colchester, there was also much damage in the epicentral region, and it is likely that similarities between Folkestone and Colchester will strengthen as more analysis is conducted; the shallow depth of both earthquakes and a ‘soft’ geological environment resulting in a concentration (and possibly amplification) of the ground-shaking in their epicentral areas.

Of course none of these areas lies near one of the Earth's active Plate Boundaries, such as the famous San Andreas Fault Zone in San Francisco. These are known as "intraplate" earthquakes, and placing intraplate earthquakes such as the Folkestone event into a geological context is always difficult. Most British earthquakes are understood to occur as a result of reactivation of ancient structures in response to the current stress regime, which is dominated by Atlantic widening. While one may speculate that Dover Straits seismicity is associated with the western end of the North Artois Shear Zone, it is difficult to be certain about the seismotectonics of this area.

If you think you are experiencing an earthquake, you should exit the building you are in - earthquakes do not kill people, buildings do. Failing that (and even outside stay clear of the exterior of buildings where falling masonry might land) you should place yourself in a door frame or under a sturdy piece of furniture such as a stout table.