Japan withdraws erroneous M9.9 earthquake warning

The Japan Meteorological Agency withdrew an erroneous earthquake early warning on 16 October after greatly overestimating the magnitude of a quake near the Kamchatka Peninsula. At about 12:40, it warned of strong shaking from Hokkaido to the Tokai region, citing magnitude 9.9 and a predicted maximum intensity of 7. Tokyo Shimbun and Yomiuri reported that the warning was cancelled at 12:48. TBS reports gave cancellation times of about 12:49 or 12:50. The agency said the actual earthquake was magnitude 6.9, at a depth of about 160 kilometres. Hakodate recorded intensity 1, and no intensity 2 or above was observed in Japan. [ 8 , 11 , 14 , 22 , 24 , 28 ]

An agency official said a formula used to calculate magnitudes for domestic earthquakes had been applied to an event with an epicentre far from Japan, producing an excessive value, Nikkei reported. When predicting shaking intensity, the system used another point closer to Japan as the epicentre, leading to a warning over a wide area. The agency apologised and said it would continue investigating why this happened. It denied a cyberattack. Tokyo Shimbun reported that no unauthorised external access to the agency's system had been confirmed. [ 22 , 24 ]

Nikkei and Tokyo Shimbun reported that this was the first cancellation of a warning-level alert. Tokaido Shinkansen services were temporarily suspended between Shin-Yokohama and Toyohashi after a disaster-prevention system activated. Yomiuri reported that trains resumed at about 12:55. Nikkei reported that JR Central said that evening the early warning was not the direct cause of the suspension. At a third press conference beginning at 22:40, the agency said countermeasures taken in the past had not worked, NHK reported. [ 4 , 22 , 24 , 28 ]