Study: 70% chance big quake will hit Tokyo within 4 years

Tokyo has a 70% probability of being hit by a magnitude-7-plus earthquake by 2016 because of seismic activity since last year's devastating quake and tsunami, about 25 years sooner than the Japanese government has estimated, according to predictions by Japanese university researchers.

If a magnitude-7.3 earthquake hits under northern Tokyo Bay, up to 11,000 people are likely to die and about 850,000 buildings would be unusable or destroyed by fire, The Yomiuri Shimbum says.

Tokyo University researchers made their calculations based on data from the Japan Meteorological Agency, which has recorded a dramatic increase in seismic activity after the magnitude-9 Great East Japan earthquake. The government's 30-year prediction is based on data before the March 11 quake.

Using the new data, the team from the university's Earthquake Research Institute says that using the 30-year window, the probability that the Tokyo region will be hit by a maghitude-7 quake rises to 98%, The Wall Street Journal writes.

Since the March disaster in the Tohu region of the main island, there has been a fivefold increase in quakes in the Tokyo metropolitan area.

Here's what one of the researchers told the Journal:

"The balance has changed since March 11," Shinichi Sakai, a research associate at the Earthquake Research Institute, told JRT. Mr. Sakai said the March 11 quake jerked the fault lines underground in a way that has changed the coastal landscape as well as the sea bed below. It also mounted pressure on nearby sea floors like those beneath Hokkaido and the Kanto region. If the rate of smaller earthquakes persist, it is likely Tokyo will see a big one strike at its doorstep in the near future.

"It's the same as when one person in a line of people holding hands falls then those around him are likely to get pulled down too," said Mr. Sakai. "The Kanto region is similarly being affected by the March 11 earthquake."

Sakai said pinpointing the exact location of a big quake is impossible, but researchers will try to narrow the possibilities.

Regardless of where it hits, he said, "the government, individuals and corporations should prepare for that" occurring within the next four years.

The BBC has a map of tectonic plate movements.

The last time Tokyo was hit by a major earthquake was in September 1923. The magnitude-7.9 Great Kanto quake killed 105,000 to 140,000 people in the Tokyo area, most from collapsed buildings and fire that consumed wooden structures.

- USA Today