
A seismic event coming in at 5.1 on the moment magnitude scale occurred at 10:00 a.m. local time in North Korea. Initial reactions, including from South Korean authorities, suggest that the incident is due to a man-made explosion. In simple terms, it appears that North Korea may have tested a nuclear device. The U.S. Geological Survey shows that the site of Wednesday morning’s seismic event is close to the North Korean nuclear site at Punggye-ri and is also close to the area where North Korea detonated a nuclear device in February 2013. If this event is confirmed as a nuclear test, it will be North Korea’s first test of the sort since 2013.

Initial factors suggesting a nuclear test include the seismic event’s location (both it and the February 2013 test took place at 41.30N, 129.10E), the fact that it took place at 10:00 a.m. sharp (people and their governments like scheduling things on the hour; earthquakes less so), and a similar magnitude reading as North Korea’s last nuclear test in February 2013 (both events measured at 5.1 on the moment magnitude scale). According to the Comprehensive Nuclear Test Ban Treaty Organization’s calculation, the estimated the yield of the nuclear device testing in February 2013 was 6-9 kilotons. Given the magnitude measurement of Wednesday’s event, the yield of this device is likely similar. Critically, this means that it is highly unlikely that North Korea tested a thermonuclear device (otherwise known as H-bomb), despite claiming to have developed one successfully last year.

North Korea is due to make a “special announcement” at 12:30 p.m. local time, South Korea’s Yonhap News reports.