Japan earthquake. Photo: Shutterstock Japan’s Meteorological Agency issued an emergency earthquake warning across parts of the country on October 16 after its early-warning system mistakenly estimated a magnitude 9.9 earthquake near the Kuril Islands. The actual earthquake, which struck near Russia’s Kamchatka Peninsula, had a preliminary magnitude of 6.9.
The warning was issued at 12:40 p.m. Japan time, following an earthquake recorded at around 12:38 p.m. The alert covered areas from Hokkaido in northern Japan to the Chubu region in central Japan.
According to the JMA, the warning was triggered because its earthquake early-warning processing system incorrectly placed the epicenter in the Kuril Islands and substantially overestimated the earthquake’s magnitude. The agency said the reason for the error was still under investigation.
The alert was subsequently canceled after strong shaking failed to materialize.
The JMA’s preliminary assessment placed the earthquake’s epicenter near the Kamchatka Peninsula, at coordinates 50.0 degrees north and 158.1 degrees east, with a depth of approximately 160 kilometers.
The strongest shaking recorded in Japan reached seismic intensity 1, the lowest level at which shaking is observed on the country’s seismic intensity scale. The reading was recorded in Hakodate, on the northern island of Hokkaido.
The agency also reported that there was no tsunami threat from the earthquake.
In its official statement, published at 2 p.m. on October 16, the JMA confirmed that the warning had been issued because the system incorrectly identified the epicenter and estimated a magnitude of 9.9. It said it would provide further information once the cause of the overestimation had been established.
Japan’s Earthquake Early Warning system uses seismic data to estimate an earthquake’s location, magnitude and expected shaking, allowing authorities and the public to take protective action before stronger tremors arrive.
Such warnings are based on rapidly processed information, and the JMA acknowledges that magnitude estimates can be inaccurate, particularly in certain earthquake scenarios.
The October 16 incident highlights the impact that an incorrect estimate can have when it triggers an alert across a broad area. The JMA has not yet identified the cause of the error and has said it will announce its findings once the investigation is complete.