Saturday morning 28 April 2007

As I drive between horse and hounds, the host of the Radio 4 programme remarks on the number of emails about 'the Earth tremors in the Deal area'. I curse that it happened now, rather than in six months time when my new Open University course Volcanoes, Earthquakes and Tsunamis will be up and running, because it might have persuaded a few more people to sign up. I decide the hounds can wait a while, and stop off at home to use the internet. The British Geological Survey website shows nothing yet although it happened nearly an hour ago, but the United States Geological Survey has reacted more quickly. They claim a magnitude 4.7 quake (on the Richter scale), 10 km deep very close to the coast, and BBC online news reports toppled chimneys and cracked walls which makes its effects (locally at least) pretty strong for the UK.  (Some hours later the British Geological Survey announce that the magnitude as only 4.3, and that the epicentre was in mid-Channel).

The global earthquake picture from the United States Geological Survey showing earthquakes in the week before 09:08 British Summer Time on 28 April. The small red square over South East England marks the Kent earthquake, which was during the previous hour. Orange squares are in the previous day. The bigger the square, the bigger the quake.
[For image copyright information please see http://www.usgs.gov/info_policies.html,]

In the global scheme of things, this was a just a minor quake. Britain is not near a plate boundary, so quakes are far rarer - and mostly much smaller - than those around the Pacific rim or along the collisional mountain belt that stretches from the Mediterranean to the Himalayas. The last one similar to this in the UK was centred near Dudley in 2002. Seeing the pictures of the fallen masonry littering the streets of Folkestone, makes me realise how fortunate it was that the quake happened at the weekend. Twenty-four hours earlier, many more people would have been injured on their way to work or school.

It seems that lots of people ran outside as soon as they felt the quake. It is fortunate that the shaking lasted only a few seconds and so was over by the time most people emerged; running outside during an earthquake is actually a very bad idea. It is about as foolish as rushing onto the beach to see what's happening if you notice that the tide appears to have gone out suddenly - because that is a sign that a tsunami is imminent.

Hazard awareness during an earthquake is one of the things we will be teaching in the new course. If you are indoors when an earthquake begins, you should stay inside and get underneath a table (for protection in case your ceiling or roof collapse). If you run outside while the quake is still in going on you risk exposing yourself to falling masonry or glass. Only after the quake should you try to get clear of buildings.

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Since posting this I've written a subsequent blog entry on the Kent earthquake.

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

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