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?
-- Jeffrey Lewis, cross-posted at Arms Control Wonk.com
UPDATE 10/10/06 1:14 AM: Noah here. Looks like the LA and NY Times have both picked up (sorta) on what the good Wonk was sayin'.
Throughout history, the first detonations of aspiring nuclear powers have tended to pack the destructive power of 10,000 to 60,000 tons 10 to 60 kilotons of conventional high explosives.
But the strength of the North Korean test appears to have been a small fraction of that: around a kiloton or less, according to scientists monitoring the global arrays of seismometers that detect faint trembles in the earth from distant blasts...
Philip E. Coyle III, a former director of weapons testing at the Pentagon and former director of nuclear testing for the Lawrence Livermore National Laboratory, a weapons design center in California, said the small size of the test signaled the possibility of what might be described as a partial success or a partial failure.
As first tests go, this is smaller and less successful than those of the other nuclear powers, he said.
Perhaps the North Koreans wanted to keep it small, he added. But if it turns out to be a kiloton or less, Dr. Coyle said, that would suggest that they hoped for more than that and didnt get it.
UPDATE 10/10/06 8:45 AM: Rumor alert! Stratfor is pretty sure that the Nork nuke -- "about one-fortieth of the Nagasaki blast" -- was a dud, too. But, just to be on the safe side, the intel service offers up "three possible explanations for the apparently small yield: the North Koreans deliberately detonated a very small device, they tested a larger device but it failed to execute properly, or the explosion was not caused by an atomic device."
Possibly the North Koreans wanted to show that they had the technology but did not want to appear too threatening, so they minimized the size. Or they could be demonstrating the ability to use lower-yield nuclear mines or artillery shells that would protect North Korea by blocking strategic passes into the country, and would possibly threaten Seoul but would not pose a significant threat elsewhere. Also, the water table is high in the area of the blast; maybe they were being careful not to break into the aquifer.
These are all good reasons, but the counterargument is that if you are going to go nuclear, go nuclear. North Korea does not have a pressing need -- or history -- of being subtle, so a small blast doesn't fit in with its plan...
What if the North Koreans didn't go nuclear, but detonated a large chemical explosive in an underground chamber? It would take a lot of explosive to yield that result, but it is not impossible. A chemical explosion would have a different seismic signature than a nuclear one, and therefore geologists should have already discounted this theory; but the analysis is going to take up to two days, according to the White House. It is certainly not beyond the North Koreans to fake a nuclear explosion, and there have been some big explosions in North Korea that have been mistaken, for a short period of time, for something nuclear. But there is no evidence, beyond our speculation, for this theory.
UPDATE 10/10/06 8:51 AM: Interesting counter-argument from Trent Telenko in the comments. Since North Korea has "had the complete design specifications for a Chinese missile-ready nuclear warhead of the plutonium implosion type for years," thanks to the A.Q. Khan network, this dud may be more dangerous than it seems.
