Japan remains on high alert for a possible mega earthquake

Japan continues to be on high alert for a massive earthquake, which its meteorological agency says could take place after a 7.1-magnitude earthquake struck southwestern Japan's Miyazaki Prefecture last Thursday at the edge of a tremulous seabed zone along the Pacific coast known as the Nankai Trough. 

The Japan Meteorological Agency (JMA) has issued its first-ever advisory on higher-than-usual risks of a megaquake, warning that another major earthquake could occur along the Nankai Trough in the coming week following the Miyazaki quake.

On Wednesday, the second-to-last day of the megaquake advisory, no significant crustal movements or seismic activities have been observed, said the JMA.

The Nankai Trough quake advisory panel, a special committee to evaluate the risks of Nankai Trough quakes, stated that the chance of a larger earthquake occurring after a magnitude 7 tremor is relatively higher than usual, being once in a few hundred cases.

Earthquakes with a magnitude larger than 8 are considered megaquakes. Japan estimates that the next Nankai Trough megaquake could be as powerful as magnitude 9.1.

"People in areas that would be affected by such a disaster should review evacuation procedures and stay vigilant for a week," said Naoshi Hirata, a professor from the University of Tokyo and also the chairman of the panel, during a press conference held by the JMA.

As a precaution, high-speed trains are slowing down, which has led to travel delays during the summer holiday in Japan; people have rushed to buy water and other supplies for emergencies, causing a shortage of relevant goods.

The Nankai Trough is a 700-kilometer-long subduction area, which refers to when tectonic plates slip beneath each other. Most of the world's earthquakes and tsunamis are caused by the movements of tectonic plates, and the most powerful ones usually occur in subduction zones.

At the Nankai Trough, severe earthquakes have been recorded every 100 to 200 years, according to the advisory panel. The last such earthquakes occurred in 1944 and 1946, both measuring 8.1 in magnitude, resulting in at least 2,500 total deaths and thousands more injured, as well as tens of thousands of homes destroyed.

If a megaquake occurs in the Nankai Trough this time, a total of 323,000 deaths are expected, and the amount of loss will surpass $1 trillion, said the Japanese government.