Japan’s Aomori quake triggers rare advisory, testing how the country communicates megaquake risk

On a frigid Monday night in December, sirens cut through the streets of Hachinohe as residents grabbed coats, blankets and car keys and headed for higher ground. Walls had just rattled hard enough to send dishes and furniture crashing to the floor. Smartphones flashed tsunami alerts. Within minutes, long lines of headlights snaked away from the Pacific coast of northern Japan’s Sanriku region.

A powerful offshore quake — and a limited tsunami

The offshore earthquake that triggered that late-night flight on Dec. 8 was powerful by any measure: a magnitude 7.5 temblor, according to the Japan Meteorological Agency, striking at 11:15 p.m. local time under the Pacific off Aomori Prefecture at a depth of about 55 kilometers. The U.S. Geological Survey measured it at magnitude 7.6. Strong shaking reached the upper 6 level on Japan’s seismic intensity scale in Hachinohe, a city of about 220,000, and was felt widely across northern Honshu and into Hokkaido.

Yet by dawn, it was clear this was not another 2011.

The quake generated only small tsunami waves, up to 70 centimeters at Kuji Port in neighboring Iwate Prefecture and about 50 centimeters on Hokkaido’s Pacific coast. There were no deaths and 47 reported injuries across Aomori, Iwate and Hokkaido, most of them minor. Authorities tallied roughly 2,300 damaged structures in Aomori, including seven collapsed homes, and limited disruptions to power, water and transportation.

An unprecedented advisory raises stakes

Instead, the most consequential aftershock may have been institutional. Within hours, for the first time since a new system was introduced in 2022, the Japan Meteorological Agency issued a “Subsequent Earthquake Advisory” warning that the probability of a far larger quake — magnitude 8 or stronger — had risen roughly tenfold along the Hokkaido–Sanriku segment of the Japan Trench.

Officials stressed they were not predicting a disaster, but signaling that the risk in the coming week had climbed to around 1%.

“We cannot rule out the possibility that a much larger earthquake could occur in the same region,” agency officials said in a technical briefing, noting that the March 2011 magnitude 9.0 Tōhoku quake was preceded two days earlier by a magnitude 7.2 foreshock off Miyagi Prefecture. “We ask residents to remain alert to strong tremors and tsunamis.”

The advisory, which covered a wide swath of offshore waters from eastern Hokkaido down past Aomori and Iwate, turned what might have been a “near miss” story into an uneasy real-time test of how Japan now lives with — and communicates — seismic risk.

Evacuations and a winter-night response

Prime Minister Sanae Takaichi convened an emergency response headquarters in Tokyo and urged people along the Pacific coast from Hokkaido through northern Honshu to move quickly if they were within tsunami zones.

“Please evacuate to higher ground or a safe building away from the coast and rivers, and stay there until authorities declare it is safe to return,” she said in televised remarks.

Chief Cabinet Secretary Minoru Kihara repeated the message through the night, asking residents “to go to higher ground or seek shelter until advisories were lifted,” and urging people not to approach shorelines to watch the waves.

According to central government figures, roughly 90,000 people in Aomori, Iwate and Hokkaido were instructed or strongly urged to evacuate coastal areas as a precaution. Local governments opened hundreds of evacuation centers, including schools and community centers; Self-Defense Forces bases in Hachinohe took in residents and vehicles, providing blankets and hot drinks.

At the peak, more than 9,000 people were staying in shelters across at least five prefectures.

In Hachinohe, convenience store owner Nobuo Yamada told public broadcaster NHK he had “never experienced such a big shaking” in his life. Shelves emptied onto the floor, he said, but he added that “luckily” the electricity stayed on in his neighborhood.

Localized damage and disrupted transport

The quake’s physical impacts, while serious, were localized. Aomori Prefecture reported damage to 849 houses and hundreds of commercial buildings, welfare facilities and schools. Parts of the Port of Hachinohe and several smaller ports experienced ground cracking and liquefaction, with wharves heaving and pavement buckling. Two small fires were reported in Aomori City. About 1,360 households in Aomori and Iwate temporarily lost water service due to damaged pipes. Power cuts affected several hundred homes but were largely restored within hours.

Transport networks were briefly disrupted. The Tohoku Shinkansen bullet train and some conventional lines in the Tohoku and Hokkaido regions were halted for inspections, then suspended again after strong aftershocks, including a magnitude 6.7 event on Dec. 12 that prompted fresh, low-level tsunami advisories. At New Chitose Airport near Sapporo, a partial ceiling collapse and cracks in the domestic terminal stranded about 200 passengers overnight.

Nuclear facilities report no safety threats

The earthquake also brushed up against one of Japan’s deepest anxieties: nuclear safety. The epicentral region lies near several major nuclear-related facilities, including the Higashidori Nuclear Power Station and the Rokkasho nuclear fuel cycle complex in Aomori, and the Onagawa Nuclear Power Station farther south in Miyagi Prefecture.

All of those facilities were offline at the time of the quake. Plant operators and the Nuclear Regulation Authority reported no abnormalities threatening safety, though they cited minor incidents such as water spilling inside some buildings. Government spokespersons repeatedly emphasized that there had been no radiation leaks and that monitoring would continue.

Preparedness shaped by 2011 — and a new communications challenge

For many along the Sanriku coast, the quake and tsunami alerts reopened memories of March 2011, when towering waves overtopped defenses, killed nearly 20,000 people and triggered a triple meltdown at the Fukushima Daiichi plant. Since then, coastal communities have built or raised concrete sea walls, updated evacuation maps, posted new signage and drilled repeatedly for the next emergency.

On Dec. 8 and 9, those systems — and the habits they fostered — were on display. Television footage showed people heading in an orderly fashion to designated shelters, many in heavy winter clothing and masks, carrying blankets and emergency bags. Fishermen moved boats and gear. Local officials used loudspeakers and community networks to guide residents away from low-lying areas.

“After 2011, people here don’t hesitate when they hear a tsunami warning,” one local official in Iwate told Japanese media. “They know exactly where to go.”

At the same time, the unprecedented “megaquake” advisory tested how the public understands extremely low-probability, high-impact risks. A 1% chance over a week is still small, but 10 times higher than the baseline probability the government had previously estimated for a magnitude-8-class event along the Hokkaido–Sanriku subduction zone.

What scientists say about the Japan Trench segment

Seismologists on a government earthquake research panel said the Dec. 8 shock fit longstanding expectations for magnitude-7 to 7.5 interplate earthquakes in this stretch of the Japan Trench, where the Pacific Plate dives beneath the Okhotsk microplate. The rupture area overlapped with the northern portion of the zone that slipped in the 1968 magnitude 7.9 Tokachi-oki quake and sat just north of where a magnitude 7.6 earthquake struck in 1994.

That does not mean, they cautioned, that the risk of a larger event has been eliminated.

Long-term government scenarios for an Hokkaido–Sanriku megaquake and tsunami envision a worst case in which an earthquake in the magnitude-8 to 9 range sends waves up to 30 meters high into bays famed for amplifying tsunami energy. In those models, as many as 199,000 people could die nationwide, with economic losses running into the hundreds of billions of dollars.

Aftershocks fade, but the lesson lingers

The advisory issued after the Aomori quake — which was lifted about a week later — is part of a new attempt to bridge the gap between catastrophic scenarios and day-to-day public messaging. Disaster management experts say the challenge is to encourage people to prepare — securing furniture, checking evacuation routes, stocking emergency supplies — without causing panic or eroding trust if the worst does not occur.

In coastal communities already facing aging populations and economic decline, even moderate damage adds to a sense of cumulative strain. Ports must be repaired, fishing operations interrupted, and schools and hospitals inspected before normal routines resume. For some residents, repeated evacuations have become part of life.

By late December, after dozens of aftershocks and the lifting of both tsunami advisories and the subsequent earthquake advisory, most of northern Japan had returned to something close to normal. Students went back to class, trains resumed regular timetables and repair crews patched cracked quays and roadways along the Sanriku coast.

On paper, the Dec. 8 Aomori earthquake will likely be recorded as a strong but ultimately manageable event: a major offshore jolt, dozens injured, significant but localized damage, no fatalities. In practice, it may come to be remembered as the night Japan rehearsed — not in a drill but under real pressure — how to respond not only to the disaster that struck, but to the possibility that the next one could be far worse.