Japan issues potential mega-earthquake advisory for northern coastal areas after quake

After Monday's powerful earthquake, the country's Meteorological Agency also issued a tsunami alert

Published Apr 20, 2026  •  2 minute read

This photo shows a warning message on a screen from a live feed on NHK with tsunami alert after an earthquake hit northern Japan, in Tokyo on April 20, 2026. Photo by PHILIP FONG /AFP via Getty Images

An advisory has been issued for the northern coastal area of Japan for an increased risk of a possible mega-earthquake.

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This comes after a major earthquake earlier in the day, which could induce a potential mega-quake.

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The Japan Meteorological Agency and the country’s Cabinet Office said there’s a 1% chance of a mega-quake happening on the northern coast in the next week or so.

A powerful earthquake rocked an area near the Chishima trough earlier on Monday.

Residents urged to prepare for emergency

Residents of Japan were urged to raise their preparedness for an emergency, such as packing emergency food and having a grab bag ready in case an earthquake hits. Japanese officials noted the advisory is not a quake prediction.

The mega-quake advisory is the second for the area in months. The first was issued after a major quake in December, but no major quake subsequently happened.

The 7.5 magnitude quake in December left dozens injured.

After Monday’s powerful earthquake, the country’s Meteorological Agency also issued a tsunami alert, with residents seeking safer grounds. No major injuries or damages were reported.

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Late Monday afternoon, an earthquake registered a preliminary magnitude of 7.5 off the coast of Sanriku, with a depth of about 10 kilometres, the agency noted.

An official of the Japan Meteorological Agency speaks near a monitor showing a tsunami alert during a news conference at the agency in Tokyo, Monday, April 20, 2026, after an earthquake that struck off the northern Japanese coast. Photo by Masanori Kumagai /AP

Tsunamis detected

An 80-centimetre tsunami was detected at the Kuji port in the Iwate prefecture within an hour of the earthquake, with a smaller tsunami (40 centimetres) recorded at another port in Iwate.

Tsunami alerts and advisories are still in place in Japan; the tsunami threat from the quake has long passed, according to the Pacific Tsunami Warning Center in the U.S.

The Japan Meteorological Agency urged residents to stay away from the coast or along rivers and take shelter on higher ground. They were also warned about possible aftershocks for about a week.

Iwate and three other prefectures issued non-binding evacuation advisories to more than 128,000 residents.

No abnormalities have been detected at the country’s nuclear power plants, the Nuclear Regulation Authority reported.

Fifteen years ago, a 9.0-magnitude earthquake and tsunami smacked parts of northern Japan, resulting in more than 22,000 deaths and displacing nearly half a million people from their homes.

After a tsunami hit the Fukushima Daiichi nuclear power plant on March 11, 2011, some 160,000 people fled their homes in Fukushima because of the spewed radiation. About 26,000 residents haven’t returned and have resettled elsewhere as their hometowns remain off-limits or have lingering radiation concerns.

– With files from The Associated Press

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