Nerves rattled in Japan as alert for magnitude 9.9 quake withdrawn minutes later

Key Points:

• The Japan Meteorological Agency (JMA) issued a false earthquake early warning on Friday, predicting a magnitude 9.9 quake that would affect a large area of Japan, but no significant shaking occurred in the country.
• The initial alert was triggered by a magnitude 6.9 quake off Russia’s Kamchatka Peninsula, but the JMA overestimated its magnitude and mislocated the epicenter, leading to the erroneous warning that was later withdrawn.
• This incident marked the first time the JMA rescinded an emergency earthquake warning, which caused public confusion and disruption, including a temporary shutdown of the Tokaido Shinkansen line.
• The JMA attributed the false alarm to applying a domestic magnitude formula to an offshore earthquake and using inconsistent location data in calculations; an investigation is ongoing to determine the precise cause.
• Similar false alarms have occurred in the past due to sensor noise or data errors, and the JMA emphasized that its early warning system operates automatically without real-time human monitoring of calculations.