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Yield of North Korea's Second Nuke
Evaluating North Korea's nuclear technology
Ludwig De Braeckeleer (ludwig)     Print Article 
Published 2009-05-28 03:24 (KST)   
This article has only been lightly edited.  <Editor's Note>
"We have successfully conducted another nuclear test on 25 May as part of the republic's measures to strengthen its nuclear deterrent."

KNCA news agency, Monday May 25th 2009

At 0054 GMT Monday, a seismic event occurred in the north-eastern region of North Korea around the town of Kilju, near the site of North Korea's first nuclear test.

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"The test was safely conducted on a new higher level in terms of its explosive power and technology of its control," the KNCA news agency said.

"The results of the test helped satisfactorily settle the scientific and technological problems arising in further increasing the power of nuclear weapons and steadily developing nuclear technology." [1]

Recent reports from South Korean intelligence sources had reported unusual activity at the Kilju test site. [2]

"This is absolutely predictable, even though I thought they would do it later, allowing some time for tension to mount," said Andrei Lankov, a Seoul-based expert on North Korea who teaches at Kookmin University. [3]

Last Friday, before leaving campus, this writer asked a former student to be ready to analyze North Korea next nuclear test. [4]

Location and Time

The International Monitoring System셲 (IMS) seismic stations registered a seismic event at 41.2896 degrees North and 129.0480 degrees East at 00:54:43 GMT (08:54 local time). [5]

The US Geological Survey confirmed the location of the event: 41.306째N, 129.029째E with a horizontal accuracy of +/- 3.8 km. [6]

Explosion, not Earthquake

In all likelihood, the explosion is man-made as the area is not active seismically. Moreover scientific tests can distinguish an explosion from an earthquake.

According to a diplomat close to the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), the tremor was not an earthquake. [7]


The system of seismic stations operated by the CTBTO detected a tremor with the magnitude 4.5 on the Richter scale. [8]

According to a message posted on the CTBTO website, "the event셲 magnitude is slightly higher than in 2006, measuring 4.52 on the Richter scale, while in 2006 it was 4.1. Considerably more seismic stations picked up the signal this time: 23 primary seismic stations compared to 13 in 2006." [9]

South Korea officials reported "an artificial earthquake" measuring at 4.4 on the Richter magnitude scale. The agency initially said it measured 4.5. [10]

The US Geological Survey put the magnitude as equivalent to a 4.7 earthquake. [11]

Beside the time and the location of the "event", seismic waves can also reveal the magnitude of the explosion. In very good approximation, the magnitude of body waves is proportional to the logarithm of the yield in kilotons: Mb = 4.26 +0.97 log (Y). A kiloton is equivalent to 1,000 tons of TNT. [See figure]

In October 2006, the author used this equation to estimate the yield of the first North Korea nuclear test at 0.2 kiloton. [12]

The office of John Negroponte, the US National Intelligence Director confirmed that the size of the explosion was less than 1 kiloton. [13]

According to the equation mentioned above, the magnitude reported by South Korea, the CTBTO and the US Geological Survey translate in yields of 1.39, 1.76 and 2.84 kilotons of TNT equivalent respectively.

The US bomb dropped over Hiroshima was between13 and 18 kilotons. [14] For reference, the first French test device had a yield of 65 kilotons. [15]

Although, the yield of the second nuke appears slightly greater than the first one, it is still rather low for a plutonium fission device and indicates that North Korean nuclear scientists have not yet fully mastered the nuke technology.


Analyst Martin Kalinowski at the University of Hamburg estimates the yield at being from 3 to 8 kilotons. I am baffled by this analysis as a yield of 8 kilotons corresponds to a magnitude of more than 5.1. [16]

Alexander Drobyshevsky, a Russian Defense Ministry spokesman, confirmed that North Korea had conducted a subterranean nuclear test and stated that the strength of the explosion was between 10 and 20 kilotons. Again, I failed to understand the statement of the Russian Defense Ministry as a yield of 20 kilotons corresponds to a magnitude of about 5.5! [17]

"According to the Korea Institute of Geoscience and Mineral Resources, a 4.4 magnitude is equivalent of 5.2 kilotons of TNT in strength, the JoongAng Daily reported". [18] This information is simply incorrect.

And to completely confuse the issue, South Korea Defense Minister Lee Sang-Hee told a parliamentary hearing that a 4.4 magnitude may mean a nuclear detonation of anywhere between 1 and 20 kilotons. [19] That statement is utter nonsense.


The low yield estimated by this writer appears to be in excellent agreement with the current US official analysis.

A senior U.S. military official has stated that "the seismic data indicated a relatively small bomb of around 1.5 kilotons." [20]


1. Text of the North Korean Announcement of Nuclear Test

2. N. Korea Conducts 'Successful' Underground Nuclear Test

3. Ibid.

4. American biophysicist C. Leidy was present when I told Mrs. Sonia Castro that I thought a second test was imminent.

5. CTBTO's Initial Findings on the DPRK's 2009 announced nuclear test

6. USGC Website
Magnitude 4.7 - NORTH KOREA

7. UN body: North Korea tremor "very close" to 2006 test site

8. CTBTO's Initial Findings on the DPRK's 2009 announced nuclear test

9. Ibid

10. N. Korea conducts second nuclear test following rocket launch

11. USGC Website
Magnitude 4.7 - NORTH KOREA

12. N.K. Nuclear Test: Evidence and Unknowns

13. US confirms N Korea nuclear test

14. Little Boy

15. History of French Nuclear Tests in the Pacific
[Part I ] 1966-1974: Atmospheric tests

16. Second nuclear test conducted by North Korea on 25 May 2009

17. Russia confirms N.Korea nuclear test


19. N Korea defies world, conducts n-test

20. Korean Blast Draws Outrage

Ludwig De Braeckeleer has a Ph.D. in nuclear sciences. Ludwig teaches physics and international humanitarian law. Ludwig can be reached at: dr.ludwig@hotmail.com
©2009 OhmyNews
Other articles by reporter Ludwig De Braeckeleer

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