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

The system allows for either a warning or a lower-level alert to be sent out. Thursday was an alert, advising people to be prepared to evacuate.

And, anecdotally, it seems to have worked. Even in a country used to receiving alerts on their phones, the “Nankai Trough” effect – and threat of the “Big One” – made people stop and take notice.

“One thing I did when I saw the advisory was to check what we have at home and make sure we are prepared, since I have not done that for a while,” admitted Masayo Oshio.

And this has been replicated along the Pacific coast.

In Nichinan, Miyazaki Prefecture, near the epicentre of Thursday’s 7.1, officials were inspecting the conditions of already-opened evacuation shelters. In Kochi Prefecture, western Japan, 10 municipalities opened at least 75 evacuation shelters by Friday morning , according to Kyodo news agency.

The thermal plant operator Jera Co., a joint venture between Tokyo Electric Power Company Holdings Inc. and Chubu Electric Power Co., said it was on emergency alert, reaffirming communication routes with fuel carriers and evacuation protocols for piers.

In the town of Kuroshio, also in Kochi, elderly residents and others were urged to evacuate voluntarily to safer locations. Officials of Wakayama Prefecture, western Japan, confirmed evacuation routes in co-operation with local municipalities.

Prof Geller – for all his scepticism – says it is a good opportunity to “make sure you’re doing all the routine precautions you should be doing anyway”.

“Have a week’s worth of water on hand, some canned food, and then maybe have some batteries for your flashlight,” he advises.

Additional reporting by Chika Nakayama and Jake Lapham