Japanese team detect gradual seafloor caving near Nankai Trough

Japan revises 30-year probability rate of Nankai Trough megaquake

A government panel has said that it now thinks a huge earthquake will occur along the Nankai Trough with a probability of 60% to 94.5% or higher within the next 30 years.

In a report issued Friday, the Earthquake Research Committee widened the probability range for a magnitude 8 to 9 earthquake occurring off the country's Pacific coast from "around 80%" it had previously announced. The change was due to unreliabilities in the past ground uplift data from Muroto Port in Kochi Prefecture and nonconstant plate strain accumulation.

"An actual earthquake is an unpredictable natural phenomenon," said Naoshi Hirata, honorary professor at the University of Tokyo and head of the panel. "We can't clearly say when it will happen. It may be more than 30 years away but may come within a year."

Megaquakes have occurred along the Nankai Trough once every 90 to 150 years. The last one, with an estimated magnitude of 8, happened in 1946.

The long-term earthquake risk assessment report also showed a separately calculated 20-50% probability range.

Although it cannot be scientifically determined which assessment is superior, the panel said, "the higher chances of a Nankai Trough quake should be highlighted" to raise local residents' awareness of an imminent disaster.

In March, the government said in its new estimate that if a magnitude 9 earthquake occurs along the trough, up to around 298,000 people would die and the country's economic loss would amount to ¥292 trillion.