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Earthquakes

They're capable of destroying entire cities, causing landslides, fires, tsunamis and even shifting the North Pole! Earthquakes are thought to have killed approximately 1.5 million people in the last hundred years alone...

Earthquakes can be caused by erupting volcanos, meteor impacts or underground explosions as a result of nuclear testing. Most, however are naturally occurring, caused by movements of the earth's plates.

The scientific study of earthquakes (seismology) is relatively new. Before the eighteenth century occurrences were recorded as fanciful theories as to why they occurred - one being that they were caused by air rushing out of caverns deep inside the earth.

The Earth is made up of huge pieces of flat rock called tectonic plates. The shifting or rubbing of these plates causes huge amounts of energy to be released, resulting in seismic waves.

A 'fault' is where two plates meet. The San Andreas fault extends over 650 miles of land, making California one of the most active earthquake areas in the world. As American geologist, William Hammond put it: 'Earth is a very slow form of Silly Putty'.

Due to its high number of volcanos, Japan's earth crust is very unstable. This causes approximately 1,000 earthquakes each year. Most are mild and cause little or no destruction.

The US Geological Survey estimates that three million earthquakes, mostly undetectable, happen every year. That's one every 11 seconds!

The 1906 San Francisco earthquake, which killed 700 people, was felt 400 miles away in Los Angeles. Despite fire raging all around, one of the buildings to survive was A.P Hotaling's Whiskey Warehouse. One local poet wrote: 'If, as some say, God spanked the town for being frisky, why did he burn the churches down and save Hotaling's Whiskey?'

Earthquake predictions still cannot be pinpointed accurately within months or even years, but once the quake has ruptured seismologists can determine the magnitude within seconds.

The Boxing Day tsunami that devastated Thailand in 2004 was caused by a magnitude 9.3 earthquake under the Indian Ocean. The fault shook for at least eight minutes (as opposed to the typical 30 seconds) and Earth's gravity balance was so altered that the North Pole shifted by an inch. Get the lowdown on the North Pole with our Polar factfile. Hear an eerie underwater recording of an earthquake on the Live Science website.

The Scottish Naturalist, John Muir was in Sierra Nevada when the 1872 Owens Valley earthquake struck. He later wrote: 'The strange thrilling motion could not be mistaken, and I ran out of my cabin, both glad and frightened, shouting 'A noble earthquake! A noble earthquake!' feeling sure I was going to learn something.'

Different cultures around the world have various legends regarding the cause of earthquakes. One Indian legend has seven serpents sharing the task of holding up the Earth; when one finishes its turn and another moves into place, people will feel a jolt.

Reports tell of animals apparently foretelling earthquakes hours or even days before occurring. Villagers in Bang Koey, Thailand, followed a herd of stampeding buffalo from the beach to higher ground minutes before the tsunami struck.

In April 2003, the Russian newspaper Pravda reported tremors in Iran measuring five on the Richter scale. Russian seismologists believe they were caused by the bombing in Iraq. Analysis has shown that earthquakes can begin in seismologically active areas two to four weeks after bombings take place.

Northwest Wales is one of the most seismically actives places in the UK. In 1984, a quake measuring 5.4 was recorded there. On average, it is thought that an earthquake hits the British Isle every four days, but quakes above five on the Richter scale are very rare. Read more about British natural disasters on the BBC website.

Experts believe global warming and the resulting rise in sea levels could cause Earth's tectonic plates to shift, seeing an increase in the number of earthquakes. If you don't want the earth to move, best go green.

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