TOKYO, Japan: A government panel in Japan on Thursday said that it has slightly increased its estimate of the likelihood of a “megaquake” hitting the country within the next 30 years, now placing the probability at up to 82 percent.
Experts say that such an earthquake, potentially measuring between 8 and 9 in magnitude, could trigger colossal tsunamis, result in hundreds of thousands of fatalities, and cause billions of dollars in damage.
The Earthquake Research Committee said it had enhanced its estimate of the probability to between 75 and 82 percent from between 74 and 81 percent previously.
The focus is on a subduction megathrust earthquake along the Nankai Trough, an 800-kilometer (500-mile) undersea trench running parallel to Japan’s Pacific coast.
This trench marks the zone where the Philippine Sea tectonic plate is “subducting” — or gradually sliding — beneath the continental plate on which Japan rests.
As the plates shift, they can become stuck, accumulating immense energy that is released when they abruptly break free, triggering potentially massive earthquakes.
According to the government’s Headquarters for Earthquake Research Promotion over the past 1,400 years, megaquakes in the Nankai Trough have occurred every 100 to 200 years.
“It’s been 79 years since the last quake, and the possibility of another quake occurring is rising every year at a pace of by about one percent,” an official of the Earthquake Research Committee’s secretariat told AFP.
According to government estimates in 2012 smaller islands off the main coasts could be inundated by tsunamis over 30 meters (100 feet) high. In densely populated regions of Honshu and Shikoku, massive waves could strike within minutes.
In August last year, the Japan Meteorological Agency (JMA) issued its first megaquake advisory under guidelines established following the catastrophic Tohoku earthquake and tsunami in 2011.
It added that the possibility of a new major earthquake along the Nankai Trough was higher than normal after a magnitude 7.1 jolt that injured 15 people.
The advisory was lifted again after a week but caused shortages of rice and other staples as people refilled their emergency stores.
In 1707, the entire Nankai Trough ruptured simultaneously, triggering an earthquake that stands as the second most powerful in Japan’s recorded history.
That quake — which also triggered the last eruption of Mount Fuji — was followed by two powerful Nankai megathrusts in 1854, and then two in 1944 and 1946.
