At 2 a.m. on December 9, the Japan Meteorological Agency issued an emergency alert warning of the potential occurrence of a magnitude 8 or stronger mega-earthquake off the coasts of Hokkaido and Sanriku. Residents in Aomori, Iwate, and Miyagi Prefectures were urged to heighten preparedness and re-examine evacuation plans. The region, scarred by the devastating 2011 Great East Japan Earthquake that claimed over 20,000 lives, has once again been thrust into anxiety.
According to the Asahi Shimbun, people were advised to secure furniture, confirm evacuation routes and shelters, and — particularly in areas vulnerable to tsunamis — sleep in clothing suitable for quick escape or keep emergency supplies at the bedside.
This was the first alert of its kind since the system was introduced in 2022. It followed a magnitude 7.5 earthquake off Aomori’s coast the night before, which shattered windows and triggered a 70-centimeter tsunami. Although approximately 30 people were injured, no fatalities were reported. Compared with the January 2024 Noto Peninsula earthquake (magnitude 7.6), which resulted in over 50 deaths within 24 hours, damage was considered relatively limited. Experts noted the difference in epicenter depth: 16 km in the Noto quake versus 54 km in the recent Aomori tremor.
The Meteorological Agency explained that global seismic statistics indicate roughly a 1% chance of a magnitude 8 or greater earthquake within one week following any quake of magnitude 7.0 or stronger. “In the worst-case scenario, an earthquake comparable to the Great East Japan Earthquake must be considered,” the agency stated.
Prime Minister Sanae Takaichi urged residents to act: “Please implement disaster-prevention measures based on the principle of protecting your own life,” she said.
Experts emphasize that earthquakes cannot be predicted — only probabilistically estimated. The 1% likelihood may seem low, but it is more than ten times higher than the usual weekly probability for the region, which typically remains below 0.1%. Professor Fumihiko Imamura of Tohoku University told NHK that magnitude 7-level earthquakes occur in the area every 20 to 30 years, corresponding to a weekly probability of 0.06–0.09%.
The alert has caused concern not only because it refers to the possibility of another magnitude 7 quake, but specifically one exceeding magnitude 8 — a level releasing approximately 32 times more energy than a magnitude 7 tremor.
History gives that warning added weight. Just two days before the catastrophic 2011 quake, a magnitude 7.3 tremor struck the same offshore zone. It is precisely this pattern that has revived collective trauma among the Japanese public, prompting renewed debate over preparedness for a worst-case seismic event.
