Major Earthquake Strikes Northern Japan: Tsunami Warnings and "Mega-Quake" Advisory

Date: Monday, April 20, 2026

Time of Occurrence: 4:52 PM – 4:53 PM JST

A powerful earthquake struck off the northeastern coast of Japan today, triggering immediate tsunami warnings across northern prefectures and prompting the Japanese government to issue a rare advisory regarding an increased risk of a "mega-quake" in the coming days.

Earthquake Figures and Specifics

The seismic event originated in the Pacific waters near the Chishima trough (off the Sanriku coast). Preliminary data from the Japan Meteorological Agency (JMA) and the USGS provided the following details:

• Magnitude: 7.5 (Preliminary JMA) / 7.7 (Revised Cabinet Office)

• Depth: 10 km to 19 km (approx. 6–11 miles)

• Epicenter: Approximately 100 km (62 miles) off the coast of Miyako, Iwate Prefecture.

• Seismic Intensity: Registered a Lower 5 on the Japanese Shindo scale of 7 in parts of Aomori, Iwate, and Miyagi. Buildings in Tokyo felt a Shindo 3, with swaying lasting several minutes.

Tsunami Observations

The JMA initially issued a tsunami warning for waves of up to 3 meters (10 feet). While the threat was later downgraded, several significant waves were recorded:

LocationTsunami Height Observed Kuji Port, Iwate 80 cm (2.6 feet) Miyako Port, Iwate 40 cm (1.3 feet) Hachinohe Port, Aomori 30 cm (1 foot) Erimo, Hokkaido20 cm (0.6 feet)

Official Press Conferences & Government Response

Japan Meteorological Agency (JMA)

At a press conference held at 6:00 PM JST, JMA officials warned that the region is in a high-activity phase. They highlighted a 1% chance of a follow-up "mega-quake" occurring within the next week (significantly higher than the standard 0.1% baseline). Residents were urged to remain vigilant for the next 2–3 days especially.

Prime Minister Sanae Takaichi

Prime Minister Takaichi addressed the nation shortly after the quake, visibly breathless as she confirmed the activation of a crisis management team.

"Residents in areas where tsunami warnings have been issued should immediately evacuate to higher ground... we are still confirming material damage but will proceed with full disaster response efforts."

Nuclear Regulation Authority (NRA)

The NRA held a brief session stating that all nuclear facilities in the region, including the Fukushima Daiichi and Onagawa plants, were inspected immediately. No abnormalities or radiation leaks were detected.

Impact and Infrastructure

• Transportation: The Tohoku Shinkansen (bullet train) service was suspended between Tokyo and Shin-Aomori stations, leaving passengers stranded on platforms and in stationary cars.

• Casualties: One injury was confirmed in Aomori Prefecture due to a fall; however, no major fatalities or large-scale structural collapses have been reported as of Monday evening.

• Defense: Maritime Self-Defense Force SH-60K helicopters were deployed to the Sanriku coast for aerial damage assessments.

Public Advisory: Officials continue to remind the public to keep "grab bags" ready and to avoid coastal areas and river mouths until all advisories are officially cleared.