Japan’s Nankai Trough megaquake – can you predict it?

The disaster that hit southwestern Japan on Thursday appeared to be unimportant.

The storm warning was immediately reduced and the earthquake of magnitude 7.1 did much harm.

However, a caution that had never been issued prior to the earthquake was soon followed by it.

There was, Japan’s weather agency said, an increased chance of a “major disaster”. A planned vacation to a conference in Central Asia will be canceled by the country’s prime minister for the following week.

For many in Japan, feelings turned to the “big one”- a once-in-a-century collapse that many had grown up being warned about.

Worst-case scenarios predict more than 300, 000 dead, with a wall of water potentially 30m ( 100ft ) striking along the East Asian nation’s Pacific coast.

Which sounds terrifying. Despite this, Masayo Oshio left with a crippling sense of confusion.

” I am baffled with the advisory and do n’t know what to make of it”, she admitted to the BBC from her home in Yokohama, south of the capital, Tokyo.

I kept asking myself,” Is this it? We are unable to identify disasters, and we have been told that the big one will strike in one moment.” However, I do n’t believe it to be real.

But, what is the “big one”, can it be predicted- and is it possible to reach any time soon?

Japan is a land used to disasters. It sits on the Ring of Fire and, as a result, experiences about 1, 500 tremors a month.

The vast majority do much harm, but there are some- like the one which struck in 2011 measuring scale 9.0, sending a wave into the north-east beach and dying more than 18, 000 individuals.

However, in the worst-case scenario, the one that regulators fear might affect in this more densely populated area of the south could be even more dangerous.

Taus of people have already died from disasters that occur along the Nankai Trough, a region of geological activity that stretches along Japan’s Pacific coast.

The second-largest earthquake ever recorded in Japan occurred in 1707 when a tear along its whole 600km size occurred, and Mount Fuji erupted in the same year.

These so-called “megathrust” disasters tend to affect every hundred years or so, usually in groups: the last people were in 1944 and 1946.

In the next 30 years, according to experts, there is a 70 % to 80 % chance that a magnitude 8 or 9 earthquake will strike somewhere along the trough, with worst-case scenarios suggesting it would inflict trillions in damage and possibly kill hundreds of thousands of people.

And this long-awaited event is the “original definition of the” Big One,” according to geologists Kyle Bradley and Judith A Hubbard.

“The history of great earthquakes at Nankai is convincingly scary” so as to be concerning, the pair acknowledged in their Earthquake Insights newsletter on Thursday.

Robert Geller, a University of Tokyo professor professor of volcanology, refutes that statement.

He told the BBC,” The release of the notice monday has almost nothing to do with science.”

This, he argues, is because while disasters are known to be a” scattered phenomenon”, it is” certainly possible to tell in progress whether a collapse is a foreshock or an aftershock”.

However, only about 5 % of earthquakes are “foreshocks”, say Bradley and Hubbard.

But, the 2011 disaster was preceded by a 7.2 scale foreshock, they note- one which was mostly ignored.

The Japan Meteorological Agency ( JMA ) used the warning system for the first time on Thursday in an effort to stop another disaster of this magnitude.

But, critically, while it told citizens to become prepared, it did not tell people to leave. However, they were willing to play down any substantial imminent risk.

The JMA stated that while a new significant earthquake is more likely than usual, it does not indicate that it will ever occur.

However, Fumio Kishida, the prime minister, announced he had abandoned his plans to leave Japan to “ensure our arrangements and connections are in get.”

Given that this was the first time for an advisory had been issued, he added that he worried that people would be “feeling anxious.”

Masayo Oshio does not seem to be, nevertheless.

” I feel that the state is overplaying it”, she said.

Prof Geller was more withering, saying the advice was” not a valuable piece of information”.

The program allows for the sending of either a reminder or a lower-level notice. Thursday was an sensitive, advising people to be prepared to leave.

And, interestingly, it seems to have worked. Also in a land used to receiving alerts on their phones, the” Nankai Trough” result- and danger of the” Great One”- made people stop and take notice.

” I checked what we have at home and made sure we are prepared,” Masayo Oshio said,” One thing I did when I saw the advice was to make sure we are prepared.”

Along the Pacific coastline, this has been done as well.

In Nichinan, Miyazaki Prefecture, near the centre of Thursday’s 7.1, officers were inspecting the circumstances of already-opened removal homes. In Kochi Prefecture, northern Japan, 10 towns opened at least 75 removal tents by Friday night, according to Kyodo news organization.

Jera Co., a cooperative venture between Chubu Electric Power Co. and Tokyo Electric Power Holdings Inc., confirmed that the infrared plant operator was on an emergency alert and that it had established departure protocols for bridges.

In the city of Kuroshio, even in Kochi, old citizens and others were urged to evacuate deliberately to safer locations. Representatives of Wakayama Prefecture, northern Japan, confirmed removal roads in co-operation with local communities.

Despite his skepticism, Prof. Geller claims that this is a good time to “make sure you’re doing all the regular steps you should be doing anyway.”

” Have a year’s worth of water on side, some canned foods, and then maybe had some chargers for your flashlight”, he advises.

Chika Nakayama and Jake Lapham provided more investigating.