JAPAN - Up to 323,000 people could die if three earthquakes occur simultaneously along the Nankai Trough, killing about 70 per cent of victims in subsequent tsunami, according to new predictions by two Cabinet Office panels.
The panels on Wednesday released predictions of damage that would be caused by a magnitude-9 Nankai Trough triple quake. This is the largest triple quake expected to occur in the trough--which stretches from off Shizuoka Prefecture down to Shikoku and Kyushu--with the so-called Tokai, Tonankai and Nankai earthquakes happening simultaneously.
The size of the predicted focal area is twice that of the magnitude-8.7 triple quake predicted by the government's Central Disaster Management Council in 2003.
One of the study panels was tasked with estimating the height of tsunami and the area of inundated regions, while the other was a working group assigned to predict damage that would be caused by the quake and tsunami. The working group determined a quick evacuation could reduce tsunami deaths by 80 per cent, and called on the central and municipal governments concerned to secure evacuation facilities and routes.
The study panel in March released its predictions on maximum seismic intensity levels and the heights of tsunami. It improved the accuracy of its calculations for the latest predictions, while also expanding the information to include areas predicted to be inundated.
Meanwhile, the working group combined several potential tsunami patterns and kinds of tremors to predict possible damage based on different seasons and times of day when the quake could occur.
For the worst-case scenario in which 323,000 people could die, the working group made its prediction based on an assumption that the quake would occur at midnight during winter, when many people are expected to be home, and cause serious damage in the Tokai region.
The number of people who could perish in this scenario is 17 times greater than the figure in the Great East Japan Earthquake in March 11, 2011. About 18,800, including both dead and missing persons, were lost in that disaster.
The latest prediction of fatalities is 13 times higher than the predicted death toll of 25,000 from a previously expected triple quake, released by the government's Central Disaster Management Council in 2003.
According to the working group's predictions, 623,000 people could be injured and 311,000 people could require rescue.
In another scenario, about 32,000 people could die if the Nankai quake occurs at noon in the summertime, when many people are expected to be away from home, and causes serious damage in the Shikoku and Kyushu regions. This represents the case with the lowest death toll among the predictions.
Alternatively, if the triple quake occurs at 6 p.m. in wintertime, when many people use fires for things like cooking and heating, up to about 2.39 million buildings could collapse or burn down.
The working group also estimated the effects of disaster prevention measures.
For example, if 70 per cent of people concerned started evacuating within 10 minutes after a midnight quake and took refuge in tsunami evacuation buildings, the tsunami death toll would drop by up to 80 per cent.
As of 2008, the national average of buildings made earthquake-resistant was 80 per cent. If the ratio of earthquake-resistant buildings were increased to 90 per cent, the number of collapsed buildings could be reduced by about 40 per cent.
The study panel predicted that up to 1,050 square kilometers of land would be inundated, 1.8 times more than the area flooded in the Great East Japan Earthquake and tsunami.
The predicted heights of tsunami do not differ much from the prediction released in March, with the highest reaching 34 meters in Kuroshio and Tosa-Shimizu, both in Kochi Prefecture.
The Cabinet Office will announce its predictions on economic damage, including the effects on electricity supply, water and sewage, and transportation, as early as this autumn. It will also develop countermeasures against a possible Nankai quake during winter.
Masaharu Nakagawa, state minister for disaster management, said at a press conference Wednesday that the government aims to create a special law by merging several existing laws related to the Tokai, Tonankai and Nankai earthquakes.