It appears that North Korea managed to pull off a nuclear bomb test. The USGS recorded the event as a 5.1 magnitude earthquake 1 km underground in the early morning. US geologists noticed the earthquake because it occurred in an area where there really isn’t any kind of tectonic activity–a clear sign that something unusual was going on.
“Indications that the test had taken place first emerged when U.S. seismologists reported a disturbance on Tuesday morning in North Korea centered near the site of the secretive regime’s two previous atomic blasts. The area around the epicenter of the tremor in northeastern North Korea has little or no history of earthquakes or natural seismic hazards, according to U.S. Geological Survey maps. The disturbance reported Tuesday had a magnitude of 5.1 — upgraded from an initial estimate of 4.9 — took place at a depth of about 1 kilometer, the USGS said. Kim Min-seok, a spokesman for the South Korean defense ministry, said the magnitude of the “artificial tremor” suggested the size of the blast could be in the order of 6 to 7 kilotons, more powerful than the North’s two prior nuclear tests. That calculation, though, was based on the USGS’s initial estimate of a 4.9-magnitude seismic disturbance, he said. A 5.1-magnitude tremor could indicate a 10 kiloton explosion.”
A 10 kiloton explosion is big. For perspective, the bomb ‘Little Boy’ used on Hiroshima was estimated at 15 kilotons.
What I find fascinating is that, despite the intense ban on outside communication for North Korean citizens, the USGS has already recorded 8 responses on their self-reporting ‘Did You Feel It?’ online survey. 3 people in Cheongjin reported feeling a moderate quake, one person in Kilju (27 miles northwest of the blast) reported felling a strong tremor, as did one person in Hoemun. Here is the community intensity map for the event. As of the time of this posting, it looked like this: