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An updated estimate shows that North Korea's nuclear test in September 2017 was equivalent to 250 kilotons of TNT, an explosive efficiency 16 times higher than the bomb launched on Hiroshima during the Second World War. The blast was also an order of magnitude stronger than the previous five tests in the country.
New research published this week in the Journal of Geophysical Research: Solid Earth provides new estimates for an underground nuclear test conducted by the Democratic People's Republic of North Korea on September 3, 2017. The bomb exploded at the test site Punggye-ri nuclear reactor Mount Mantap produced 250 kilotonnes of TNT, according to the new study. Given the uncertainties, the force could reach 328 kilotonnes. The 2017 test was also an order of magnitude higher than any previous tests performed on the site from 2006 to 2016, indicating a sudden increase in capacity.
The authors of the new study have developed a more accurate estimate taking into account the geology of the region. To determine the power of these weapons by far, scientists study the seismic waves produced by these tests.
North Korea withdrew from the 1968 Nuclear Non-Proliferation Treaty in 2003 and began testing nuclear weapons in 2006. The country has now completed six trials in total, each stronger than the previous one. . But as new research shows, the difference between the fifth and sixth tests is particularly alarming. The passage from about 20 kilotons to 250 kilograms means a dramatic increase in North Korea's nuclear potential.
"The scary thing is that it was such a big device."
"From 2006 to 2016, North Korea gradually increased the size of events, from about 1 kilotonne to about 20 kilotonnes. The first events seemed to not work very well because they were exceptionally small, "said Thorne Lay, co-author of the study, a seismologist at the University of California at Santa Cruz, in an American Geophysical Union. Press release. "And then in a year they climbed to 250 kilotons. What's scary is that it was such a big device.
This revised estimate is not totally surprising. The 2017 test triggered a magnitude 6.3 earthquake, an event that literally displaced the mountain. The underground explosion also caused the collapse of the nuclear chamber at the Punggye-ri nuclear test site.
A study conducted in 2018 evaluated the performance of the device at 209 kilotonnes. In American intelligence, it is common practice to apply a margin of error of a factor of two, so that reported estimates range from 120 to 304 kilotonnes. The new study further improved the force, to 250 kilotons with an error margin of between 148 and 328 kilotons. At the upper limit, this is nearly 22 times the force of the bomb dropped on Hiroshima, which was 15 kilotons.
To develop their updated estimates, researchers analyzed previously compiled data on how sound travels through different types of rocks. A sound wave, for example, will behave differently when it is propagated in granite compared to sandstone. And as the geology of Mount Mantap and its environs is not well known, scientists had to use earlier nuclear test explosions conducted at Punggye-ri to calibrate their models.
An important element to consider was how underground explosions bounced off the surface like an echo – an effect that distorts seismic recordings at a distance. Keeping this in mind, the researchers estimated "the relative size of the bombs by finding a combination of depth and efficiency that offsets the surface's sound reflection," as pointed out by the author. AGU in its press release.
"They modeled what the reflection would look like for different yields and depths and solved what the signal would look like if you did not have to consider this wave of return. The most impressive thing in the document for me is the similarity of these waveforms. That's what gives me confidence that they did a good job, "said geologist Steven Gibbons, who was not involved in the new study, in the AGU press release. "I think the authors pushed this project to the limit. I would be surprised if we can get stricter constraints on absolute returns without additional information. "
Regarding the type of weapon used in the 2017 test, Lay said it was a reinforced fission bomb or a modest fusion device, the latter also being called a thermonuclear bomb. or hydrogen. Fusions bombs combine hydrogen nuclei to form helium, which creates a huge explosive potential. The most powerful of them, the Bomba Tsar of 1961, produced more than 50,000 kilotons.
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