Some 1,800 people in the Izu and Ogasawara island chains in the Pacific could be killed, mainly by tsunami, if the Nankai Trough off central and western Japan experiences a major temblor, the Tokyo Metropolitan Government warned Tuesday.

In the worst-case scenario mapped out by the metropolitan government’s working group on quakes, as many as 1,774 residents, or about 6.5 percent of the roughly 27,400 inhabitants of the Tokyo-jurisdiction islands, could die, assuming a 9-magnitude temblor strikes the trough at midnight in winter.

Some 1,764 people, or almost all of the estimated fatalities, would be the result of tsunami, according to the scenario, which also estimates 1,282 structures could be destroyed, including 1,160 due to the waves.

Naoshi Hirata, who heads the seven-member working group, underscored to reporters at the metro government that constant preparation is key to mitigating casualties in the event of a major earthquake, including prompt evacuations to high ground before tsunami hit.

“The (March 11, 2011) Great East Japan Earthquake taught us that we can be hit by tsunami higher than we’ve ever seen. . . . It’s essential that the islanders are made aware of their local geography and the potential of such waves striking, and to be prepared if a big quake occurs under the sea,” said Hirata, a professor at the Earthquake Prediction Research Center at the University of Tokyo.

The group’s casualty estimates were based on the Nankai Trough quake-tsunami scenario the Cabinet Office’s Central Disaster Prevention Council came up with last August for the greatest damage sustained in areas under Tokyo’s jurisdiction. That report put the death toll, covering 30 prefectures, at 323,000 people, but it didn’t provide a casualty breakdown for the islands managed by Tokyo.

Thus the metro government came up with its own assessment, a metro official said.

Under the metro scenario, the Izu chain’s island of Niijima, located about 160 km south of central Tokyo, would have the most fatalities, at 1,299, followed by 268 in nearby Kozushima, and 1.68 percent of Niijima would experience a quake intensity of lower 6 on the Japanese seismic intensity scale to 7, while the rest of the island would experience an upper 5.

Another scenario, estimating a lower death toll on the islands, says Niijima could see tsunami reaching 30.16 meters around 17 minutes after the Nankai Trough is hit by a 9-magnitude temblor.

The metropolitan government plans to provide the information to the islands’ municipalities so they can map out detailed disaster mitigation plans.

The Izu chain has nine inhabited islands, while the Ogasawara cluster has two.

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