The Japanese weather agency said Thursday that the risks of a massive earthquake occurring around the Nankai Trough that runs along the Pacific coast have become higher than usual, issuing the first such advisory of its kind.
The advisory was released just hours after a magnitude 7.1 quake rattled southwestern Japan, with its focus located in waters off Miyazaki Prefecture, on the western edge of the Nankai Trough. It does not recommend evacuation but calls for reviewing routine quake preparedness and staying alert for about a week.
In the worst-case scenario, a powerful temblor could shake a wide area of Japan -- from the Kanto region centering on Tokyo to the southwestern Kyushu region -- and high tsunami waves could engulf the coastal areas of Kanto to Okinawa, according to the Japan Meteorological Agency.
The Japanese government has predicted there is a 70 to 80 percent chance of a magnitude 8 to 9 quake occurring along the Nankai Trough within the next 30 years, with a 2012 estimate showing that the number of deaths could reach up to 323,000.
Naoshi Hirata, the head of an advisory body to the weather agency that assessed the latest quake, said the probability of a major earthquake along the Nankai Trough has now increased by "several times" compared to usual.
The Nankai Trough extends a distance of approximately 800 kilometers where the Eurasian and Philippine Sea tectonic plates intersect.
Hirata also said he cannot predict the exact areas that will require disaster preparedness but called for caution against any eventuality.
He also said he feels there is no need to refrain from swimming in the sea but advised beachgoers to check where to shelter in place in the case a tsunami warning is issued.
The Japanese weather agency started operating a system to release special information regarding the Nankai Trough quake in 2017, which is activated when an earthquake with magnitude 6.8 or above hits areas where megaquakes are predicted or when unusual crustal movements are observed at plate boundaries.
A notification that investigation is under way will be released within 30 minutes and an emergency meeting of the agency's Nankai Trough quake advisory body will be convened.
If the risk of a potential major earthquake is determined at the meeting along the Nankai Trough, the agency will issue a "major earthquake advisory" or a "major earthquake warning" possibly in around two hours from the quake.
When a warning is issued, residents living in coastal areas could be asked to evacuate in advance and remain away for about a week.
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