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North Korean Nuclear Test More Than Twice as Powerful as Last Blast
WASHINGTON -- The explosive yield of the nuclear device detonated last week by North Korea is estimated to be 2 1/2 times more powerful than the force of the nation's last blast in 2009, scientists say.
In announcing the Feb. 12 test, Pyongyang claimed the successful detonation of a "miniaturized device." Assuming North Korea is telling the truth, the use of a smaller device coupled with a bigger yield suggests the country is seriously advancing its ability to make viable nuclear warheads that could be fitted to a ballistic missile.
The exact yield of last week's test is unlikely to known so long as the North refuses to disclose technical data from its nuclear weapons trial program, which might soon grow to four tests, according to South Korean intelligence officials monitoring activity at the Punggye-ri detonation grounds in the country's northeast.
Using seismic data from North Korea's 2009 and 2013 nuclear detonations, scientists at Stony Brook University in New York on Friday announced they were able to pinpoint to within 120 meters the location of last week's underground blast.
With this information, physicist James Acton of the Carnegie Endowment for International Peace concluded the North's third nuclear test took place in the same tunnel at Punggye-ri and at nearly the same depth as the 2009 blast. From this, he calculated the most recent detonation had an explosive power 2 1/2 times larger than the prior trial. Acton and other scientists emphasize that estimations at this point are preliminary.
"Essentially what the mathematics tells you is that if you know that two tests took place at the same depth ... then you can calculate their relative yields exactly. You may not know either one's absolute yield but you can determine the ratio between the two exactly," Acton said in a telephone interview.
Seismologist Paul Richards of the Lamont-Doherty Earth Observatory at Columbia University concurred with Acton's thinking, though he emphasized the inherent uncertainties in estimating North Korean nuclear test yields. "It does appear to be a test at the same depth in 2009 and so for that reason we have some confidence in saying that it is 2 1/2 to 3 times bigger but we are still uncertain about the absolute size," Richards said on Tuesday.
Nearly four years after the event, international measurements of the 2009 test are still not settled though most come down to within several kilotons of each other. The Stalinist state's first test in 2006 is widely seen as a failure, having an estimated yield of less than 1 kiloton.
Richards, who has written extensively about North Korea's nuclear tests, said the second blast had a magnitude of "around 5 kilotons but again there is considerable uncertainty." Based on this projection, the seismologist said the yield of last week's event is likely within the range of 5-15 kilotons.
By comparison, the yield of the U.S. atomic bomb dropped on Hiroshima during World War II was about 15 kilotons.
"This doesn’t help us know what the yield of the 2009 test was. What it does tell us is that they have made a significant step forward" in their nuclear testing, said Acton, a senior associate with the Carnegie Nuclear Policy Program.
The seismic movement produced on Feb. 12 measured 4.9 on the Richter Scale, according to the Preparatory Commission for the Comprehensive Test Ban Treaty. That was twice the level as the seismic tremors created following the 2009 test and even larger still than the shock waves created in 2006.
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