Japanese authorities issued a rare warning about a possible megafault in the north of the country after a magnitude 7,5 earthquake struck at 23:15 PM local time on December 8, centered off the east coast of Aomori Prefecture, south of Hokkaido. The earthquake struck at a depth of approximately 54 kilometers, and tremors were felt at level 6 on the Japanese earthquake intensity scale in several areas.

The quake injured 34 people, mostly with minor injuries, and damaged roads and buildings in the cities of Tohoku and Aomori. A tsunami of up to 70 centimeters reached ports in Iwate and Hokkaido prefectures, after which warnings were cancelled. More than ten aftershocks followed overnight, heightening concerns.

The government estimates that a mega-fault in the Hokkaido-Sanriku region could trigger a tsunami up to 30 meters (98 feet) high, killing up to 199 people, destroying 220 buildings, and causing 31 trillion yen (approximately $198 billion) in damage. Cabinet Office Emergency Management Director Tsukasa Morikubo noted:

"Based on global earthquake statistics, there is a possibility of a large-scale tremor of magnitude 8 or greater as a follow-up event."

Experts attribute the risks to shifts in the Pacific tectonic plate, similar to those that caused the 2011 disaster: a magnitude 9,0 tsunami up to 15 meters high and an accident at the Fukushima nuclear power plant, which claimed nearly 20 lives.