An offshore Pacific earthquake of the scale that hit Japan last year would trigger 34-meter tsunami, resulting in at least 323,000 deaths and devastating much of the coastline from Honshu to Kyushu, experts say.
An offshore Pacific earthquake of the scale that hit Japan last year would trigger 34-meter tsunami, resulting in at least 323,000 deaths and devastating much of the coastline from Honshu to Kyushu, experts say.
This grim scenario is the result of a radical reappraisal of a possible magnitude-9.1 earthquake in the Nankai Trough in light of the Great East Japan Earthquake that left 20,000 people dead or missing.
The estimate of fatalities in a Nankai Trough earthquake is 13 times higher than the figure offered by the central government in 2003.
Until the March 11 disaster, experts had assumed that no quake greater than magnitude-8.0 would hit the region off Miyagi Prefecture in northern Japan. Last year's earthquake was magnitude-9.0, putting it among the top five of the world's biggest quakes.
Two expert panels were commissioned by the government to offer a realistic assessment of what Japan can expect if a Nankai Trough earthquake strikes.
At the same time, the panels cautioned that the possibility of such a major disaster occurring was low. However, they called on the public to be "properly fearful" of what may lie ahead.
It is a given that the reappraisal will force the central and local governments to go back to the drawing board in assessing their disaster management plans.
The panels said proper preparations for evacuating residents from towering tsunami caused by a Nankai Trough quake could reduce the estimated fatalities to 61,000, or one-fifth of the level in the worst-case scenario.
The Nankai Trough is an oceanic trench that stretches for about 700 kilometers off the coast of Shizuoka Prefecture in central Honshu to Kyushu. It is a region where quakes frequently occur when the oceanic plate slips under the continental plate.
The grim assessment of possible damage would inevitably be much higher if a Tokai, Tonankai or Nankai quake occurred simultaneously or triggered other quakes along the region.
Much of the damage would come from towering tsunami. The area at risk covers 10.15 million square kilometers, about 1.8 times the area that was inundated after last year's massive earthquake.
One of the panels headed by Katsuyuki Abe, professor emeritus of seismology at the University of Tokyo, estimated the extent of flooding caused by the tsunami produced by the Nankai Trough quake. The other panel, chaired by Yoshiaki Kawata, a professor specializing in disaster management at Kansai University, focused on estimates of fatalities and damage to buildings.
The worst-case scenario was based on a premise of a magnitude-9.1 quake striking.
Under the scenario, 151 municipalities in 10 prefectures, ranging from Shizuoka to Miyazaki in Kyushu, would experience shaking of a maximum 7 on the Japanese intensity scale and 239 municipalities in 21 prefectures would experience shaking of upper 6 intensity.
It said tsunami of at least 20 meters would strike eight prefectures, including the islands of the Izu and Ogasawara chains that are under the jurisdiction of the Tokyo metropolitan government.
Major metropolitan areas of Tokyo, Nagoya and Osaka would be flooded, likely paralyzing economic activity because distribution routes--roads and rail transport--would be severed.
Estimates of economic loss would expand in tandem with the number of fatalities and damage to buildings and infrastructure.
In 2003, the government put the maximum economic loss from a Nankai Trough quake at 81 trillion yen ($1 trillion).
However, Kawata said, "At a minimum, an economic loss of 270 trilllion yen is possible. Rough estimates could lie anywhere between 300 trillion yen and 900 trillion yen."
Government estimates of the economic loss from the Great East Japan Earthquake range from 16 trillion yen to 25 trillion yen.
The extremely high loss estimates for the Nankai Trough quake are due to the fact the Tokai region is an important manufacturing base in Japan. Many automobile-related plants are located there.
The appraisal said the Hamaoka nuclear power plant in Omaezaki, Shizuoka Prefecture, would be under nine meters of water if work to build an 18-meter-high breakwater wall and higher embankment walls is not taken into account.
The work is expected to be completed in December.
The plant stopped operations in May 2011, two months after the Great East Japan Earthquake, at the request of Prime Minister Naoto Kan because it lies within the epicenter of a predicted major quake.
The maximum tsunami height in Omaezaki was put at 19 meters.
Chubu Electric Power Co., which operates the Hamaoka plant, has installed water-proof doors for the reactors and moved emergency generators to elevated ground 40 meters above sea level.
The utility will likely have to implement further measures because flooding in nuclear reactors would result in an automatic shutdown.
Estimates of fatalities and damage to infrastructure and buildings were based on a number of factors: the focus of the earthquake, the time it occurs, the season and wind speed. Four locations were cited as likely to experience the greatest damage: the Tokai and Kinki regions, Shikoku and Kyushu.
In the estimate for extensive damage in the Tokai region late at night in winter when winds are strong, total fatalities would reach 323,000.
Of that figure, 230,000 people would die in tsunami, 82,000 from collapsed buildings and 11,000 from fires caused by the quake. The number of injured people was put at 600,000.
Between 2.364 million and 2.386 million buildings would be swept away or burned to the ground due to the shaking, tsunami, fires as well as collapse of foundations brought about by liquefaction.
As a result, the panel estimated that 311,000 people would be trapped under the rubble of collapsed buildings and would have difficulties digging themselves out.
That is another staggering figure considering the fact that there are only 160,000 firefighters in all of Japan.