Did the earth move for you, too?

IT is unusual to see news headlines about earthquakes in the United Kingdom, and residents in the south east of Kent must be counting themselves extremely unlucky to receive so much damage to their properties.

It is reported that 73 buildings were left in such a dangerous state that residents will not be able to return for several months.

Although it is unusual for any part of Britain to experience such a damaging earthquake, tremors have been felt on a fairly regular basis, although often only enough to trouble recording instruments and not people.

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The last recorded earthquake in the UK was as recent as last Christmas when an area in Dumfries and Galloway was hit on Boxing Day.

Most earthquakes are caused by the movement of plates that make up the crust of the earth. These plates fit very tightly and move around due to thermal energy that is released from the centre of the earth.

Rocky plates do not move very easily and tension builds up in the plate boundary areas. The tension is often released very quickly and the area will experience an earthquake as the inter-boundary friction is suddenly overcome.

As plate boundary movement is relatively common, some parts of the World are particularly prone to earthquakes, such as the Pacific-rim countries (Japan, Chile, USA, Central America).

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The UK, however, sits firmly in the middle of the British Eurasian plate and according to the theory of plate tectonics should not be a seismically active area.

Despite this, due to Britain's complicated geological history there are a number of underground faults that are still active and create fairly small-scale incidents.

Kent has experienced four previous earthquake tremors during recorded history, with one event in 1580 causing the deaths of two people in London. The magnitude of that earthquake was thought to be around six on the Richter Scale, although this was, of course, not measured at the time.

A magnitude of six made that earthquake 1,000 times more powerful than the one experienced last weekend. The Richter Scale, which measures the intensity of earthquakes is a logarithmic scale, which in simple terms means that for every full point, the earthquake is thirty times more powerful.

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Thus an earthquake measuring five is thirty times more powerful than one measuring four.

While the Kent earthquake and an earlier one at Dudley in 2002 caused localised damage to property, these are likely to be about as big as the UK is ever likely to experience. This country does not sit over a major fault zone, similar to the one found at San Francisco, and we cannot expect a "big one" at any time.

While it is no consolation to the Kent victims, future earthquakes are likely to cause only minimal damage and will not lead to widespread devastation or loss of life. Although fairly rare, it is also unlikely that we will have to wait too many years before the next one.