London, March 13 (IANS) The total energy released by the megaquake in Japan was about a thousand times the combined energy of all the world’s nuclear weapons or 6.7 trillion tons of TNT.
It is a grim reminder of the fact that undersea earthquakes can be so much more devastating than those on the land. They can generate the most destructive of tsunamis, especially those occurring along substantial linear faults off the coast of Japan.
Like the New Zealand quake, the catastrophe in Japan was a result of the titanic geological forces operating around the Pacific “Ring of Fire”.
This is a 25,000-mile belt of earthquakes and volcanoes encircling the Pacific Ocean, a chain of giant fault lines which separate some of the largest of the Earth’s tectonic plates – the dozen-or-so slabs of solid rock which make up our planet’s crust.
Earthquakes are common in Japan, one of the world’s most seismically active areas. The country accounts for about 20 percent of the world’s earthquakes of magnitude 6 or greater, the Daily Mail reports.
Several continental and oceanic plates – the Pacific Plate, Philippine Plate, Eurasian Plate and North American Plate – meet in the Japan area, which is why there are so many volcanoes and hot springs across the nation.
Located in a volcanic zone so active, it is nicknamed the Pacific Ring of Fire, where catastrophic earthquakes occur several times each century.
The plates themselves consist of sheets of basalt and granite between five and 30 miles thick, underpinning both the continents and the ocean floors.
They float on the viscous, semi-molten rocks beneath the crust and are able to move, typically a few inches a year, propelled by currents deep in the mantle – the part of the Earth below the crust.
The 8.9-magnitude earthquake Friday afternoon set off huge tsunami waves, some as high as 10 metres, that rushed ashore for several kilometres along Japan’s northeastern coast, sweeping everything in their path – buildings, cars, ships and people, and killing over 1,000 people.