The Japan Meteorological Agency (JMA) issued an emergency earthquake warning at 12:40 p.m. on Friday, October 16, reporting a magnitude 9.9 quake in the Kuril Islands. Eight minutes later, the agency withdrew the Japan 9.9 earthquake alert after determining the estimate was wrong.
An earthquake did occur at around 12:38 p.m. near Russia’s Kamchatka Peninsula. The JMA put its magnitude at 6.9 and its depth at about 160 kilometers (approximately 100 miles). The strongest shaking recorded in Japan was intensity 1 in Hakodate, Hokkaido.
The automated system, however, placed the epicenter in the Kuril Islands and calculated a magnitude of 9.9, prompting a kinkyu jishin sokuho (emergency earthquake warning) for Hokkaido, Tohoku, Kanto, Hokuriku, Koshin, Tokai and the Izu Islands.
The bulletin forecast shaking up to shindo 7 (Japan’s seismic intensity scale, which ranges from 0 to 7) in Hokkaido and Tohoku. A magnitude 9.9 quake would exceed the largest ever recorded by instruments, the magnitude 9.5 event in Chile in 1960. No tsunami warning or advisory was issued.
For tips on getting ready for a major quake, see our guide on how to prepare for an earthquake and tsunami in Tokyo.
According to the JMA, this is the first time the agency has retracted a public earthquake warning since the system began operating. At a 2 p.m. press conference, Ayaki Ebita, head of the agency’s earthquake and tsunami monitoring division, apologized and ruled out a cyberattack, citing a probable software processing error.
At a second briefing at 5:30 p.m., the agency stated that the system had applied a magnitude formula intended for domestic earthquakes to one centered far from Japan. It also found that the hypocenter used to calculate the magnitude differed from the one used to forecast shaking, when the two should have been the same. The investigation is ongoing.
Central Japan Railway Co.’s quake protection system cut power to the Tokaido Shinkansen between Shin-Yokohama and Toyohashi, suspending service in both directions until 12:55 p.m.
Some mobile users also received the cancellation notice with the same chime used for the original warning, which drew criticism on social media, J-CAST News reported.
The JMA has previously issued erroneous quake data. On August 1, 2016, a magnitude 9.1 forecast for Tokyo Bay, intended only for specialist providers rather than the public, reached smartphone app users. The agency canceled it 15 seconds later. The error was attributed to noise at a single seismometer in Chiba Prefecture.
Readers putting together supplies can also refer to our emergency evacuation backpack list.
The JMA notes in its documentation on the early warning system that magnitude estimates have limitations, particularly for large earthquakes. It states that data from a single seismograph can lead to false alarms. Still, the Tokyo Metropolitan Government’s disaster guide advises residents to secure their own safety first, then check official information from the authorities.