The tremor hit at 4:53pm local time — shallow, violent, and unmistakable. Office workers in Tokyo, hundreds of kilometres from the epicentre, felt buildings sway. Along the Sanriku Coast of northern Japan, the shaking registered upper 5 on the country’s seismic intensity scale: strong enough to make walking difficult without grabbing something solid, strong enough to topple bookshelves and send dishes crashing.

Then came the warnings. A tsunami alert flashed across screens nationwide. “Tsunami! Evacuate!” NHK broadcast, over footage of ships urgently leaving Hachinohe port in Hokkaido. The Japan Meteorological Agency (JMA) urged coastal residents across three prefectures — Hokkaido, Aomori, and Iwate — to move to higher ground immediately. Waves of up to 3 metres were expected.

Within an hour, real waves confirmed the threat was not theoretical. An 80-centimetre tsunami struck Kuji Port in Iwate prefecture. A 40-centimetre wave arrived at Miyako Port, also in Iwate. Authorities warned that larger waves than those initially recorded may already have reached some areas, and that tsunami heights could increase with successive surges.

As of late evening Japan time, no major injuries or structural damage had been confirmed. The picture — still forming — was one of a serious seismic event met by a country that has spent decades engineering and drilling for exactly this.

A Shallow Quake With Real Punch

The earthquake’s preliminary magnitude was reported at 7.4 by some agencies and 7.5 by others; the JMA later revised it upward to 7.7 following further analysis. The depth was initially estimated at 10 kilometres — extremely shallow, which amplifies surface shaking — and was later revised to 19 kilometres. Shallow earthquakes of this magnitude in submarine environments are precisely the conditions that generate dangerous tsunamis.

The epicentre sat in the Pacific Ocean off northern Iwate prefecture, along the Sanriku Coast — a name seared into Japan’s national memory. This is the same stretch of coastline that bore the full force of the March 2011 disaster, when a magnitude 9.0 undersea quake triggered a tsunami that killed roughly 18,500 people and destroyed the Fukushima Daiichi nuclear plant.

That history was on everyone’s mind Monday evening, even as the early signs pointed toward a far less catastrophic outcome.

128,000 Under Evacuation Orders

Iwate and three other northern prefectures issued non-binding evacuation advisories covering more than 128,000 residents, according to Japan’s disaster management agency. Several port towns — including Otsuchi and Kamaishi, both devastated in 2011 — ordered thousands to leave.

NHK footage showed cars streaming uphill to parks and community centres serving as evacuation sites. In Tomakomai, Hokkaido, a resident told the broadcaster he had collected his child from a cram school and driven to a hilltop park, planning to wait until the alert was lifted. The scenes were orderly and familiar — the result of a country that rehearses mass evacuation the way others rehearse fire drills.

Chief Cabinet Secretary Minoru Kihara reiterated evacuation warnings in a press conference and confirmed that officials were still assessing potential damage. Prime Minister Sanae Takaichi told reporters the government had established an emergency task force and was investigating possible casualties.

“For those of you who live in areas for which the warnings have been issued, please evacuate to higher, safer places such as higher ground,” Takaichi said.

Infrastructure Holding

The disruptions were immediate but contained. Bullet train services on the Tohoku, Yamagata, and Akita shinkansen lines were suspended. Local train services in the affected region were also halted. Large buildings in Tokyo shook during the quake, though no damage was reported in the capital.

The nuclear question — always the first asked in post-2011 Japan — appeared to yield reassuring answers. The Nuclear Regulation Authority said no abnormalities had been detected at nuclear power plants or related facilities in the region. Hokkaido Electric Power and Tohoku Electric Power both have shutdown nuclear plants in the area; none are currently operating. Tohoku Electric said it was checking the impact on its Onagawa plant. The operator of the Fukushima Daini plant reported no abnormalities and no change in radiation levels.

The Fire and Disaster Management Agency said officials were assessing the situation at power stations and other critical infrastructure. As of late evening, the all-clear on that front was holding.

A Week of Warning

The JMA did not mince words about what might still be coming. Officials warned that additional earthquakes of similar magnitude could occur over the next week — standard procedure after a major event, but not a statement anyone in northern Japan takes lightly.

The agency also raised its estimated likelihood of a “megaquake” — defined as magnitude 8.0 or higher — from 0.1 per cent to 1 per cent. Such quakes typically occur at subduction zones where one tectonic plate slides beneath another, precisely the geological configuration off Japan’s northeastern coast.

Japan sits atop four major tectonic plates along the Pacific Ring of Fire and accounts for roughly 18 per cent of the world’s earthquakes despite holding just over 1.5 per cent of the global population. The country experiences around 1,500 noticeable jolts per year. Most are harmless. The ones that aren’t shape national policy.

Fifteen Years On

The shadow of 2011 is impossible to separate from any seismic event along the Sanriku Coast, and the Japanese public knows it. NHK broadcasters reminded viewers Monday evening that tsunami waves can grow in size over time, and that even an 80-centimetre surge is powerful enough to knock a person off their feet. The network has adopted a more urgent on-air tone in the years since the disaster, when some victims died because they evacuated too late or not at all.

About 160,000 people fled their homes around Fukushima after the nuclear meltdown. Roughly 26,000 have never returned — displaced by resettlement, restricted zones, or lingering radiation concerns.

Monday’s quake, while serious, appears to be an order of magnitude removed from that catastrophe. A previous 7.5-magnitude quake in December 2025 injured dozens but caused no major structural damage. The JMA issued a week-long “megaquake” advisory at that time as well.

The Pacific Tsunami Warning Center in Hawaii assessed that the tsunami threat from Monday’s quake had passed — though the Japanese warnings remained in effect, reflecting the country’s insistence on caution that borders on the institutional.

As darkness fell over the northeastern coastline, reporters broadcast live from Miyako Port where a 40-centimetre wave had arrived hours earlier. Visibility was poor. Residents stayed on higher ground. The all-clear had not come.

That is the rhythm of a country that has learned, through terrible experience, that the first wave is rarely the last, and that patience measured in hours is the cheapest insurance there is.

Sources