North Korean Nuclear Claim Draws Global Criticism (NY Times)
New York Times said:Martin B. Kalinowski, a nuclear expert at the University of Hamburg, said a seismic magnitude of 4.7 corresponded to a nuclear explosive yield of about three to eight kilotons of high explosives, with the most likely yield being four kilotons.
...But Alexander Drobyshevsky, a Russian Defense Ministry spokesman, offered a different estimate, saying that the force of the blast, which the ministry confirmed occurred at 9:54 a.m. local time in northeastern North Korea, was 10 to 20 kilotons, the RIA-Novosti news agency reported. It was unclear what information the defense ministry based its estimate on. Russia estimated the force of the 2006 blast at 5 to 15 kilotons, far higher than other estimates at the time.