Magnitude 7.5 earthquake strikes off northern Japan, triggering tsunami warnings and mass evacuations

Overview

A magnitude 7.7 earthquake (revised upward from an initial 7.5) struck 100 kilometers off Japan's Iwate Prefecture on Monday afternoon, along the Sanriku coastline where tsunamis killed tens of thousands in 1896, 1933, and 2011. The Japan Meteorological Agency issued tsunami warnings for waves up to three meters and ordered evacuations for nearly 172,000 people across five prefectures.

Observed waves peaked at 80 centimeters at Kuji Port, well below the forecast level. All tsunami warnings were lifted by Tuesday morning. At least 26 buildings were damaged in Aomori Prefecture and around 200 power outages were reported across the affected area.

Once warnings were lifted, the JMA issued a rare 'Subsequent Earthquake Advisory' covering 182 municipalities from Hokkaido to Chiba Prefecture, valid through April 27 at 5 p.m. The agency placed the probability of a magnitude 8 or greater earthquake along the Japan Trench at roughly 1 percent — ten times the normal baseline rate. Prime Minister Sanae Takaichi urged residents to continue daily activities, stay ready to evacuate, and confirm shelter locations and keep emergency supplies accessible.

Why it matters

Japan's earthquake warning and evacuation systems faced their biggest Pacific coast test since the 2011 Tohoku disaster, and performed as designed.

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Key Indicators

7.7

Earthquake magnitude (revised)

JMA revised the initial 7.5 reading upward to 7.7; USGS measured 7.4

171,957

People ordered to evacuate

Across five prefectures in northern Japan

80 cm

Highest observed tsunami wave

At Kuji Port in Iwate Prefecture, well below the three-meter warning level

Injuries reported

No deaths recorded; at least 26 buildings damaged in Aomori Prefecture

Megaquake probability (elevated)

JMA places odds of a magnitude 8+ earthquake within the next week at 1%, ten times the baseline rate of 0.1%

Nuclear plant abnormalities

Fukushima Daiichi, Fukushima Daini, Onagawa, and Higashidori all reported normal operations

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People Involved

Sanae Takaichi

Urging public evacuation readiness amid active JMA megaquake advisory through April 27

Minoru Kihara

Providing public updates on damage assessment

Organizations Involved

Japan Meteorological Agency (JMA)

Government Agency

Tsunami warnings lifted; Subsequent Earthquake Advisory active through April 27 for 182 municipalities from Hokkaido to Chiba

Japan's national agency responsible for earthquake detection, tsunami warnings, and weather forecasting, operating over 4,200 seismometers nationwide.

Timeline

11 events Latest: April 21st, 2026 · 2 months ago Showing 8 of 11

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April 2026
JMA lifts all tsunami advisories
Latest Warning

The Japan Meteorological Agency downgraded tsunami warnings to advisories and later lifted all advisories. The agency warned that earthquakes of similar scale could occur over the following week.
April 21st, 2026
JMA issues rare Subsequent Earthquake Advisory through April 27
Warning

The Japan Meteorological Agency issued a formal Subsequent Earthquake Advisory covering 182 municipalities from Hokkaido to Chiba Prefecture, warning that the probability of a magnitude 8 or greater earthquake along the Japan Trench has risen to roughly 1 percent — ten times the normal baseline of 0.1 percent. The advisory, a system introduced by JMA in 2022, remains in effect until April 27 at 5 p.m. JST.
April 21st, 2026
PM Takaichi urges evacuation readiness as daily life resumes
Government Response

Prime Minister Sanae Takaichi urged residents to continue everyday activities but maintain immediate evacuation readiness, including confirming designated shelters, checking evacuation routes, and keeping emergency supplies packed and accessible.
April 21st, 2026
Four magnitude 5.0+ aftershocks recorded; strongest reaches 5.6
Earthquake

By late evening on April 21, four aftershocks measuring Mw 5.0 or greater had occurred off the Sanriku coast, with the strongest reaching Mw 5.6 off Miyako in Iwate Prefecture.
April 21st, 2026
Building damage and power outages confirmed across affected prefectures
Damage Assessment

Authorities confirmed at least 26 buildings damaged in Aomori Prefecture and approximately 200 power outages across the impacted area. Repair crews were deployed to restore service.
April 21st, 2026
Magnitude 7.5 earthquake strikes off Iwate coast
Earthquake

A shallow earthquake at 10 kilometers depth struck approximately 100 kilometers off the Sanriku coast of Iwate Prefecture. The Japan Meteorological Agency initially measured it at 7.4 before revising to 7.5.
April 20th, 2026 • 16:53 JST
JMA issues tsunami warning for three-meter waves
Warning

The Japan Meteorological Agency issued tsunami warnings for Iwate, Aomori, and Hokkaido coastlines, forecasting waves up to three meters. Advisories for one-meter waves were issued for other parts of northeastern Japan.
April 20th, 2026 • 16:55 JST
Evacuations ordered for nearly 172,000 people
Evacuation

Japan's disaster management agency ordered evacuations across five prefectures. Residents along the Pacific coast were directed to move to higher ground or designated evacuation buildings.
April 20th, 2026
Tsunami waves observed at multiple ports
Observation

Waves reached 80 centimeters at Kuji Port, 40 centimeters at Miyako Port, 30 centimeters at Hachinohe Port, and 20 centimeters at Erimo in Hokkaido. All observations were well below the three-meter warning level.
April 20th, 2026
Takaichi establishes crisis management team
Government Response

Prime Minister Sanae Takaichi set up a crisis management team and urged residents in warning areas to evacuate immediately. Chief Cabinet Secretary Minoru Kihara confirmed no deaths or major damage.
April 20th, 2026
Tohoku and Akita Shinkansen lines suspended
Infrastructure

Bullet train service between Morioka and Shin-Aomori was halted, along with the Akita Shinkansen line. Nuclear plants at Fukushima Daiichi, Fukushima Daini, Onagawa, and Higashidori reported no abnormalities.
April 20th, 2026

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Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

March 2011

Tohoku earthquake and tsunami (2011)

A magnitude 9.1 earthquake struck 72 kilometers off the Oshika Peninsula of Tohoku at a depth of 32 kilometers, generating tsunami waves exceeding 40 meters. The tsunami overwhelmed seawalls, destroyed coastal towns, and triggered meltdowns at three reactors of the Fukushima Daiichi nuclear power plant. Nearly 20,000 people died.

Then

Japan shut down all 54 of its nuclear reactors for safety reviews. The estimated economic damage exceeded $300 billion, making it the costliest natural disaster in history.

Now

Japan overhauled its tsunami warning system, built higher seawalls along the Sanriku coast, and established stricter nuclear safety standards under a new independent regulatory authority.

Why this matters now

The April 2026 earthquake struck the same Sanriku coastline. The warning systems and evacuation protocols tested on April 20 are direct products of reforms made after 2011. The rapid, orderly evacuation of 172,000 people reflects 15 years of post-Tohoku preparedness investment.

January 2024

Noto Peninsula earthquake (2024)

A magnitude 7.5 earthquake struck beneath the Noto Peninsula in Ishikawa Prefecture on New Year's Day at 4:10 p.m. local time, generating a major tsunami warning, the first since 2011. Tsunami waves exceeded five meters along parts of the coast. The earthquake killed 703 people and destroyed thousands of buildings in rural communities.

Then

The high death toll exposed vulnerabilities in rural disaster preparedness, including aging buildings that did not meet modern seismic codes and limited evacuation routes in mountainous terrain.

Now

The disaster prompted national discussion about seismic resilience in aging rural communities and the difficulty of retrofitting traditional wooden structures.

Why this matters now

The Noto earthquake, identical in magnitude to the April 2026 event, killed over 700 people. The dramatically different outcome off Iwate, with 30 injuries and no deaths, reflects the contrast between a shallow inland quake hitting aging rural structures and an offshore quake where modern warning systems gave populations time to evacuate.

June 1896

Meiji Sanriku earthquake and tsunami (1896)

A magnitude 8.5 earthquake struck 166 kilometers off the coast of Iwate Prefecture, generating tsunami waves that reached a record height of 38.2 meters. The waves destroyed approximately 9,000 homes along the Sanriku coast and killed at least 22,000 people. Most victims had no warning because the earthquake's shaking was relatively mild onshore.

Then

Entire fishing villages along the Sanriku coast were wiped out. Recovery was slow in the largely rural, isolated communities.

Now

The disaster, followed by another devastating Sanriku tsunami in 1933, led Japan to begin developing what became the world's most advanced tsunami warning infrastructure.

Why this matters now

The 1896 disaster struck the same Iwate coastline as the April 2026 earthquake. The 130-year contrast is stark: in 1896, mild shaking gave no indication of the coming tsunami. In 2026, the JMA's seismometer network detected the quake and issued tsunami warnings within minutes, enabling the evacuation of 172,000 people before waves arrived.