El Siglo Futuro - Japan lifts 'megaquake' warning, tells people to 'go back to normal'

The week-old alert that such a catastrophe might hit the archipelago of 125 million people prompted thousands to cancel holidays and stock up on essentials, emptying shelves in some stores.

"The people of Japan are free to go back to normal lifestyles," disaster management minister Yoshifumi Matsumura said as he announced the lifting of the advisory at 5:00 pm (0800 GMT).

However, he said people should not forget measures such as securing furniture, ensuring family members know the location of evacuation shelters, and stockpiling emergency foods.

"The special call for attention ended but it doesn't mean the risk of a major earthquake has been eliminated," Matsumura told reporters.

"We ask (people) to continue to be mindful of these daily precautions and remain vigilant for a megaquake that can happen anytime, anywhere," he said.

Japan's weather agency said last Thursday the likelihood of a megaquake was "higher than normal" following a magnitude 7.1 jolt that day that injured 15 people.

That was a particular kind of tremor known as a subduction megathrust quake, which has occurred in pairs in the past and can unleash massive tsunamis.

The advisory concerned the Nankai Trough between two tectonic plates in the Pacific Ocean.

The 800-kilometre (500-mile) undersea gully runs parallel to Japan's Pacific coast, including off the Tokyo region, the world's biggest urban area and home to around 40 million people.

All segments of the Nankai Trough ruptured at once in 1707, unleashing an earthquake that remains the nation's second-most powerful on record.

That quake, which also triggered the last eruption of Mount Fuji, was followed by two powerful Nankai megathrusts in 1854, and one each in 1944 and 1946.

- Slower trains -

Japan's government has said the next magnitude 8-9 megaquake along the Nankai Trough has a roughly 70 percent probability of striking within the next 30 years.

In the worst-case scenario, 300,000 lives could be lost, experts estimate, while some engineers say the damage could reach $13 trillion, with infrastructure wiped out.

However, experts said the risk was still low and the agriculture and fisheries ministry urged people on Saturday "to refrain from excessively hoarding goods".

The statement came after supermarkets put limits on purchases including bottled water and as demand soared online for emergency items such as portable toilets and preserved food.

The megaquake warning even prompted Prime Minister Fumio Kishida to cancel a four-day trip to Central Asia last weekend.

Some bullet trains reduced their speed as a precaution and nuclear plants were instructed by authorities to double-check their disaster preparations.

- 'Convincingly scary' -

Japan sits on top of four major tectonic plates and experiences around 1,500 quakes every year, most of them minor.

The impact is generally contained even with larger tremors thanks to advanced building techniques and well-practised emergency procedures.

The Japan Meteorological Association warning was the first under new rules drawn up after a 2011 quake, tsunami and nuclear disaster that left around 18,500 people dead or missing.

The 2011 tsunami sent three reactors into meltdown at the Fukushima nuclear plant, causing Japan's worst post-war catastrophe and the world's most serious nuclear accident since Chernobyl.

"The history of great earthquakes at Nankai is convincingly scary," geologists Kyle Bradley and Judith A. Hubbard wrote in their Earthquake Insights newsletter last week.

However, there was only a "small probability" that last week's magnitude 7.1 earthquake was a foreshock.

"One of the challenges is that even when the risk of a second earthquake is elevated, it is still always low," they said.

H.Alejo--ESF