Tokyo is situated on Japan’s main Honshu island which is turn sits at the intersection of three continental plates, the Eurasian, Pacific and Philippine Sea plates, which are slowly grinding against each other, building up enormous seismic pressure that every so often is realised with ferocious force.

Volcanoes and oceanic trenches around the Pacific Basin which holds Japan have earned the area the name The Ring of Fire.

Japan accounts for about 20 per cent of the world’s earthquakes of magnitude six or greater and on average, an earthquake occurs there every five minutes.

When earthquakes occur under the sea floor, they unleash tsunamis which are often more devastating than the quake itself.

Tsunamis, from the Japanese word for harbour and wave, are vast quantities of water displaced by the violent movement of the earth’s crust.

This water moves as waves, able to travel vast distances at high speeds, sweeping over landmasses and demolishing everything in their path.

Several factors determine the height and destructiveness of a tsunami. They include the size of the quake, the volume of displaced water, the topography of the sea floor as the waves race to the coast and whether there are natural obstacles that dampen the shock.

Destruction of protective mangroves and coral reefs and the building of homes or hotels on exposed beaches are blamed as leading causes of high death tolls from tsunamis.

Kevin McCue, a seismologist at CQUniversity in Queensland, Australia, said that although the death toll was likely to be high, the quake’s distance from Tokyo, the world’s most populous city, was a blessing.

“In 1923 in the great Kanto earthquake which measured 7.9, 147,000 people died so our expectation is that many people will be killed and there will be extensive damage,” he said.

“Fortunately for Tokyo it’s a bit further north than the great Kanto earthquake was, which means the damage in Tokyo is likely to be much less.”