Japan’s ‘megaquake’ warning explained

HOW MUCH IS AT STAKE?

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

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

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

And “while earthquake prediction is impossible, the occurrence of one earthquake usually does raise the likelihood of another”, they explained.

“A future great Nankai earthquake is surely the most long-anticipated earthquake in history – it is the original definition of the ‘Big One’.”

HOW WORRIED SHOULD PEOPLE BE?

Japan is reminding people living in quake zones to take general precautions, from securing furniture to knowing the location of their nearest evacuation shelter.

Many households in the country also keep a disaster kit handy with bottled water, long-life food, a torch, radio and other practical items.

But there’s no need to panic – there is only a “small probability” that Thursday’s (Aug 8) magnitude 7.1 earthquake is a foreshock, according to Bradley and Hubbard.

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

“For instance, in California the rule of thumb is that any given earthquake has around five percent chance of being a foreshock.”