TOKYO - A Japanese geologist says he has discovered another tectonic plate under the Tokyo area, a find that may force Japan to rethink earthquake forecasts and preparations for the capital, Kyodo news agency said on Saturday.
Present government estimates say Tokyo has a 90 percent chance of being hit by a major earthquake in the next 50 years. The last massive tremor to hit the city killed 140,000 people in 1923.
By analysing data on 150,000 earthquakes that took place in the region between 1979 and 2004, Shinji Toda of the National Institute of Advanced Industrial Science and Technology deduced the existence of a plate that had previously been thought to be part of what is known as the Philippine Plate, Kyodo said.
Toda believes that the portion is a piece of the Pacific Plate that is 25 kilometres (15 miles) thick and spans 10,000-square-km (3,869 sq miles).
If Toda's findings are confirmed, the geology of the Tokyo region is even more complex than current models indicate, with four tectonic plates layered on top of one another in some areas, Kyodo said.
Japan is one of the world's most seismically active areas and accounts for 20 percent of the world's earthquakes of magnitude 6 or greater.
Toda plans to present his findings at an earth science forum that opens in Chiba, east of Tokyo, on Sunday, the news agency said.
"People say an earthquake directly under the Tokyo region is looming, without fully discussing the geology of the region," Toda told Kyodo. "We need a full re-investigation of the mechanisms by which quakes occur, including the plate structure," he added.
A government disaster prevention panel estimated in February that a magnitude 7.3 quake in Tokyo could cause $1 trillion in damage and kill more than 10,000 people.
Four tectonic plates meet in the Japan area, the Eurasian, North American, Philippine and Pacific plates.
REUTERS NEWS SERVICE
