Alerts for Subsequent Earthquakes: Stay Calm and Check Preparations on a Routine Basis

Editorial

14:42 JST, April 22, 2026

An earthquake measuring as high as upper 5 on the Japanese seismic intensity scale of 7 struck Aomori Prefecture, prompting tsunami warnings across a wide area from Hokkaido to the Tohoku region. The impact was significant, with evacuation instructions briefly issued for 180,000 people.

The areas affected by this quake overlap with those afflicted by the 2011 Great East Japan Earthquake. Many residents reportedly said that based on lessons learned from the 2011 disaster, they immediately ran to higher ground this time.

In some areas, there were traffic jams on roads leading to higher ground. Evacuation plans will likely need to be regularly reviewed in light of local conditions.

In Tokyo — far from the hypocenter — long-period ground motions that caused high-rise buildings to sway were observed.

At the Tokyo metropolitan government building in Shinjuku Ward, an elevator heading to the 45th-floor observation deck detected the shaking and stopped. It took an hour to restore service, leaving 310 people, most of them tourists, waiting on the observation deck.

Long-period ground motions were also observed during the earthquake in January this year that recorded a seismic intensity of upper 5 in Shimane and Tottori prefectures. It can be said that this is a new challenge for urban areas with many high-rise buildings and condominiums.

After the most recent earthquake, the Japan Meteorological Agency issued an advisory for subsequent quakes off the coast of Hokkaido and the Sanriku region. A lower 5 tremor occurred two days before the Great East Japan Earthquake. As earthquakes in this region can sometimes be followed by even stronger shaking, the government established this advisory system in 2022.

The first such advisory was issued in December 2025 when an upper 6 quake was recorded in Aomori Prefecture, and this is the second time for one to be issued. It is necessary to heighten vigilance about a major quake over the next week. People should check evacuation routes and their food supplies to make sure they are prepared on a routine basis.

Although the risk has increased, the probability of a subsequent major earthquake actually occurring is estimated to be about one in 100, so there is no need to worry to excess. It is important to continue normal social and economic activities, and there is no need to cancel planned events and other activities across the board.

In the area near the quake’s hypocenter, magnitude 7-class earthquakes are not uncommon. Advisories for subsequent earthquakes are expected to be issued about once every two years. Local governments should not only double-check their disaster prevention measures but also work to make residents familiar with the advisory system.

The subsequent earthquake advisory will remain in effect for one week. Since this period was set as a general guideline, it does not mean that the danger will disappear once it passes. It is vital to make a habit of earthquake preparedness.

In the wake of the earthquake, disinformation spread on social media, including in a post on X (formerly Twitter) of an AI-generated video showing a massive tsunami. Social media operators must strengthen measures such as those for swiftly deleting such content.

(From The Yomiuri Shimbun, April 22, 2026)