Earth
Japan's 9.9 Earthquake Warning: What Really Happened
Phones across Japan, from Hokkaido down to Tokyo, lit up with an alert for a magnitude 9.9 quake that never happened. The real event was a much smaller M6.9 deep beneath Russia's Kamchatka Peninsula. The Short walks through why the system overestimated it, including a sensor filter that had been switched off by mistake, and how early warnings race slower S waves using faster P waves.
The numbers
- The false M9.9 alert went out on 16 October 2026 and was withdrawn roughly eight minutes later.
- The actual quake was an M6.9 under Kamchatka; Japan's strongest shaking was intensity 1 in Hakodate.
- Every full step in magnitude releases roughly 32 times more energy.
- The biggest quake ever recorded was M9.5 in Valdivia, Chile, in 1960.
Sources cited in the video: JMA · NHK · USGS · NASA Earth Observatory
