North Korea Nuke a Dud Maybe?

Kevin Drum links to reports from the BBC and the LA Times, and poses the question. update: via Josh Marshall, Jane's Defence Weekly reports: Although details are tentative, initial and unconfirmed South Korean reports indicate that the test was a fission device with a yield of .55 kT. By comparison the nuclear bomb that was dropped on Hiroshima yielded approximately 12.5 kT. The figure of .55 kT, however, seems too low given the 4.2 register on the Richter scale. This could suggest - depending upon the geological make-up of the test site - a yield of 2-12 kT. If, however, the lower yield is correct, it would suggest that the test had been a "pre- or post-detonation" event (ie a failure), as it had been anticipated that North Korea's first nuclear test would have a significantly higher yield.