HA HA HA HA.I -- Jeffrey Lewis, crossposting from Arms Control Wonk -- love the US Geological Survey. They've published lat/long (41.294 N, 129.134 E) and Mb estimates (4.2) for the North Korean test.
There is lots of data floating around: The CTBTO called it 4.0; The South Koreans report 3.58-3.7. You're thinking, 3.6, 4.2, in that neighborhood. Seismic scales, like the Richter, are logarithmic, so that neighborhood can be pretty big. But even at 4.2, the test was probablya dud.
Estimating the yield is tricky business, because it depends on the geology of the test site. The South Koreans called the yield half a kiloton (550 tons), which is more or less -- a factor of two -- consistent with the relationship for tests in that yield range at the Soviet Shagan test site:
Mb = 4.262 + .973LogW
Where Mb is the magnitude of the body wave, and W is the yield.
3.58-3.7 gives you a couple hundred tons (not kilotons), which is pretty close in this business unless you're really math positive. The same equation, given the US estimate of 4.2, yields (pun intended) around a kiloton.
A plutonium device should produce a yield in the range of the 20 kilotons, like the one we dropped on Nagasaki. No one has ever dudded their first test of a simple fission device. North Korean nuclear scientists are now officially the worst ever. Of course, I want to see what the US IC says. If/when the test vents, we could have some radionuclide data -- maybe in the next 72 hours or so.
But, from the initial data, I'd say someone with no workable nuclear weapons (Kim Jong Il, I am looking at you) should be crapping his pants right now.
First the missile, then the bomb. Got anything else you wanna try out there, chief?