At 11:15 p.m. on Monday, a 7.5-magnitude earthquake struck off northern Japan, injuring more than 20 people. Tsunami warnings were issued for the coastal areas of Hokkaido, Aomori and Iwate prefectures. According to NHK, waves of up to 70 centimeters in height were detected at Kuji port. On Tuesday morning, the tsunami warning for the region was downgraded to an advisory. However, the Japan Meteorological Agency (JMA) has urged people to remain vigilant for aftershocks and has issued an alert for a potential megaquake. 

Earthquake Strikes in Waters Off Aomori Prefecture

Monday’s quake was centered about 80 kilometers off Aomori Prefecture, at a depth of approximately 50 kilometers. According to the Japan Meteorological Agency (JMA), it registered a seismic intensity of upper-6 on the Japanese shindo scale in the city of Hachinohe. That’s a level strong enough to make standing difficult and cause structural damage. The Fire and Disaster Management Agency said that as of Tuesday morning, 23 people have been reported injured, including one seriously. Many of those hurt were staying in a hotel in Hachinohe. 

“Based on the instruction from the prime minister, we are mobilizing all resources for assessing the damage, conducting search-and-rescue operations and implementing emergency disaster relief measures under the policy of prioritizing human life,” said Chief Cabinet Secretary Minoru Kihara at a press conference on Tuesday. He added that around 800 homes were without electricity, and that some Shinkansen and local line trains have been suspended. According to Kihara, no abnormalities have been reported at any of the nation’s nuclear power plants, though safety checks are still being conducted.

Authorities Issue Alert for Potential Megaquake 

Tsukasa Morikubo, Cabinet Office official for disaster preparedness, also held a press conference on Tuesday to speak about the likelihood of a megaquake hitting Japan that could trigger a tsunami along the Pacific coast from Hokkaido to Chiba Prefecture. “Based on the statistics of earthquakes that have occurred around the world so far, there is a possibility that a large-scale earthquake with a magnitude of 8 or higher could occur as a follow-up earthquake along the Japan Trench and the Chishima Trench off Hokkaido,” he said. 

Morikubo added, “It is unclear whether a large-scale earthquake will occur. But everyone should heed the call to take precaution to protect their own lives.” The JMA issued an alert for a potential megaquake following Monday’s earthquake. It’s the first alert of its kind since this category of warning was launched in 2022. The advisory states that the probability of a megaquake has become “relatively higher than normal.” While the likelihood of one occurring remains low, the warning has been issued to increase public caution and earthquake preparedness.

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Updated On December 9, 2025