On Monday, the Japan Meteorological Agency (JMA) issued a warning over the potential for a megaquake this week, following a 7.7 magnitude earthquake that struck off the northeast coast. The powerful quake caused a tsunami of up to 80 centimeters on the Pacific coast and triggered evacuation orders for 171,957 people in five prefectures. A 5.6 aftershock was recorded less than an hour after the main temblor, which hit off the Sanriku coast in Iwate Prefecture.
Registering upper 5 on Japan’s seismic intensity scale of 7, the undersea quake occurred at a depth of 19 kilometers. Tremors were felt as far away as Tokyo. Chief Cabinet Secretary Minoru Kihara told reporters there were no immediate reports of deaths or major structural damage. He added that there were 200 power outages across the impacted areas. Several bullet trains were affected. Authorities are now assessing the risk of a larger seismic event in the coming days.
JMA Says 1% Chance of Megaquake in Japan This Week
According to the JMA and the Cabinet Office, there is a 1% chance of a megaquake along two deep-sea trenches in the Pacific Ocean in the next week. While that may seem relatively small, it is a significant increase from the typical 0.1% chance. The alert, NHK reports, covers 182 municipalities across the prefectures of Hokkaido, Aomori, Iwate, Miyagi, Fukushima, Ibaraki and Chiba. No evacuation orders are currently in place in the affected areas.
A megaquake alert is issued by the JMA when an earthquake of magnitude 7.0 or higher occurs near specified trenches, such as the Nankai Trough or Japan Trench. It warns of an elevated likelihood of an earthquake of magnitude 8.0 or higher. The first-ever Nankai Trough megaquake advisory was issued in August 2024, when a magnitude 7.1 quake shook southern Japan. Another advisory was issued following a 7.5-magnitude quake in December.
