In Case Details Disappear in the News
I just heard the news this evening that North Korea apparently set off an underground nuclear device this Sunday. According to SFGATE.COM the test was conducted at 10:36 a.m. (9:36 p.m. EDT Sunday) near the city of Kilju (or Kilchu -- depending on your translation). The article went on to say that the USGS hadn't detected any seismic activity in that area, possibly because their sensors weren't sensitive enough.
Oddly, MyForecast.com does report a 4.2 magnitude earthquake occuring at 01:35:28 AM UTC (same time as reported test) at the coordinates 41.31N 129.11E at a depth of 0 km, which is roughly the position of Kilju City. FWIW, a 4.2 magnitude earthquake would be about 2kt of TNT worth of energy, although this would only be seismic movement, not necessarily total energy. I haven't found any more information on the relationship of seismic energy to nuclear yield yet, so if anyone has information, please comment.
I took another gander at the USGS world earthquake information site, and I noticed that at about 10:15pm EDT the USGS earthquake network now lists the North Korean earthquake. It's good to know the information is now coming in.