It’s being reported that North Korea has detonated another test nuclear device, and the USGS is showing a magnitude 4.7 quake in North Korea (the previous device test registered as a mag 4.2 one).
Using the code I mentioned when writing about the first test it appears that it was likely to be around an 11 kiloton device, significantly larger than the 2 kt device tested previously.
Mag. Energy Energy TNT TNT TNT Hiroshima
Joules ft-lbs tons megatons equiv. tons bombs
4.2 0.126E+12 0.929E+11 0.301E+02 0.301E-04 0.201E+04 0.134E+00
4.7 0.708E+12 0.522E+12 0.169E+03 0.169E-03 0.113E+05 0.753E+00
USGS image of DPRK nuclear test 2009/05/25
A yield of 11 kiloton for this test is probably too high, so is a yield of 2 kilotons for the 2006 test. The 2006 test was estimated by the US as “less than one kiloton”, and the South-Koreans estimated a yield of 800 tons. We know the magnitude of this test (4.7) and the previous one (4.2), so if we use the South-Korean figure we can estimate a yield of: 0.8 x (10^(4.7-4.2))^ 3/2 = 4.5 kiloton.