Grim numbers: potential Japan megaquake could kill nearly 300,000, cost US$2 trillion

A "megaquake" and subsequent tsunami could cause as many as 298,000 deaths in Japan and damage costing up to US$2 trillion (HK$15.6 trillion), the government said in a new estimate.

The figures have been updated from a 2014 estimate made for the potential consequences of a huge earthquake along the Nankai Trough south of Japan.

The 800-kilometer undersea trench runs from Shizuoka, west of Tokyo, to the southern tip of Kyushu island.

It is where the Philippine Sea oceanic tectonic plate is "subducting" - or slowly slipping - underneath the continental plate that Japan sits atop. The plates become stuck as they move, storing up vast amounts of energy that is released when they break free, causing potentially massive earthquakes.

The Cabinet Office's disaster management working group said up to 215,000 people would be killed by a tsunami, 73,000 by the collapse of buildings and 9,000 by fire.

But the predicted toll as a whole is lower than the 2014 estimate which said that up to 323,000 people would die.

The expected economic damage is nearly half of the country's GDP, and was up sharply from the previous estimate of 214.2 trillion yen (HK$11.11 trillion) as the new estimate accounted for inflationary pressures and updated anticipated flood areas, the report showed.

Over the past 1,400 years, megaquakes in the Nankai Trough have occurred every 100 to 200 years. The last one happened in 1946.

But in January, a government panel said the probability of such a megaquake in the next 30 years has marginally increased, with a 75 percent to 82 percent chance of it happening.

A magnitude-9 quake in 2011 that triggered a tsunami and meltdowns at a nuclear power plant in northeast Japan killed more than 15,000 people.

AGENCE FRANCE-PRESSE, REUTERS