Japan sent a false alert for a 9.9 quake on Friday. The real quake was far smaller.
The real quake struck off the Kamchatka Peninsula. It hit at around 12:38 pm Japan time.
Japan's weather agency warned of a 9.9 quake. It forecast strong shaking across much of Japan.
The alert set off alarms on phones and public speakers. Many people saw it or heard it.
The agency cancelled the alert at 12:48 pm. It said the first alert was wrong.
The system placed the quake off the Kuril Islands. The real quake was off Kamchatka instead.
No strong shaking was felt in Japan. The highest reading was shindo 1 in Hakodate.
No tsunami warning was issued. The US tsunami center said there was no danger.
A 9.9 quake would be the largest ever recorded. The record is 9.5, in Chile in 1960.
Sensors feel the first weak waves. Computers guess the size and send alerts in seconds.
If alerts cry wolf too often, people may ignore them. The next alert could be real.
When an alert sounds, stay calm. Get under a strong table and wait.
Read the full explainer: the false alert, the real quake, and what comes next.
Get the full breakdown, key numbers, and what happens next.
Read on Rive News