Guest column:Understanding the huge forces that bring total disaster
THE earthquake and tsunami that struck Japan on March 11 brought home yet again the devastating impact of natural hazards such as earthquakes, volcanoes, storms and floods that can occur with little or no warning.
Japan is a country vulnerable to these events because it is located on the famous "Pacific Rim of Fire".
The countries around the margins of the Pacific are always under threat because the earth is a very active place.
Great thick sections of the Earth's crust are in motion. Along the east coast of Japan, two of these massive sections are colliding.
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At times the collision may be rapid, almost instantaneous, and this is when an earthquake occurs. If the movement, termed a rupture, is large enough a major earthquake results.
In Japan this month the rupture was 400-500 kilometres long and the movement 7-8 metres.
If the earthquake is offshore, then the rupture leads to upward movement at the sea bed, and it is this that creates the tsunami. Because the rupture was close to land, the wave built up very quickly to huge heights, up to 20 metres in some places.
The March 11 event was huge. We all recall the Boxing Day tsunami of 2004, when over 220,000 people died in Thailand, Indonesia, India and Sri Lanka.
The Japan earthquake was of a similar size, a magnitude 9. This is what is called a Great Earthquake. People who study these events identify it as one of the largest ever; certainly the largest ever to strike Japan. We still await the final death toll.
Although Japan is a first world country, it is very difficult to immediately find out how many people are affected.
The first task is to help the living and up 500,000 people have been left homeless. Then the rescue teams try to find people buried in their houses or trapped in their cars. There will undoubtedly be amazing stories of survival.
It is likely that the final death toll count will be over 10,000.
These events are not new to Japan. The last major earthquake was in 1995, when Kobe was destroyed and 6,500 people lost their lives.
The northern coast of Honshu, where the March 11 event took place, is particularly vulnerable; in 1933 there was an earthquake and tsunami that killed 3,000 and in 1896 27,000 died in a similar event.
Thus in the future it is likely that further earthquakes and tsunamis will indeed take place.
The earthquake and tsunami threat to Britain is small. The geology of Britain is very different to that of Japan. The borders of the Atlantic Ocean are quite peaceful compared to the Pacific. We have volcanoes, but they are millions of years old and not active. We do have earthquakes, but they are very small. The most recent struck Ripon in North Yorkshire in January this year, but this was a magnitude 3.6 – thousands of times smaller than the earthquake that hit Japan.
Although the British Geological Survey in Keyworth is far inland and we don't expect to be struck by devastating earthquakes or tsunamis, we do study these events in other countries.
In 2004 when the Indian Ocean tsunami struck I began studying tsunamis from earthquakes and have been involved in four expeditions to the Indian Ocean researching that devastating tsunami. The objective is to better understand why and where tsunamis occur so as to help save lives.
Professor Dave Tappin is a tsunami and earthquake expert at the British Geological Survey, based in Keyworth.