How Seismic and Radiation Monitoring Reveal North Korea's Nuclear Secrets

By Eliza Strickland | May 27, 2009 3:47 pm

North Korea nuclear testEven before North Korea announced that it had conducted its second underground test of a nuclear weapon, scientists around the world were putting together a picture of what had happened. With a combination of seismic and radiation monitoring, scientists expect to soon have a working idea of how far the rogue nation’s nuclear program has advanced.

At 9:55 a.m. local time on Monday, two seismic monitoring stations on the Japanese coast detected seismic waves coming from the area where North Korea last tested a nuclear weapon, in 2006. The region has little natural seismic activity, and experts noted that the waves didn’t match patterns produced by earthquakes. Movements along natural fault lines transmit most of their energy through ‘s-waves’, whereas explosions at a single point release a greater proportion through compressional p-waves. In the waves detected in Japan, the s-wave component was just one-fifth that of the p-wave. “You can’t say it’s impossible for a natural earthquake, but it would be very rare,” says Gen Aoki of the Japan Meteorological Agency in Tokyo [Nature News].

Experts note that the network of blast detectors intended for the Comprehensive Test Ban Treaty, which has not yet come into force, seems to have perfectly identified the explosion as a nuclear test, despite its small size. [In 1998, the U.S. Senate] rejected the CTBT partly over fears that countries could cheat, by claiming small covert weapons tests were earthquakes. The detection of the North Korean test raises hopes that the Senate will no longer be able to object [New Scientist]. But scientists had to do more than simply show that an underground explosion had sent ripples through the earth; they also have to determine how big the bomb was, and prove that the tremors weren’t caused by conventional explosives.

The U.S. Geological Survey reported that the seismic event had a magnitude of 4.7. While calculating the power of an underground blast from its resulting shockwaves requires knowledge of the region’s geology, in this case researchers benefited from previous studies done in 2006, when North Korea detonated its first nuclear bomb at the same site. That 2006 test was believed to be a “fizzle” in which the nuclear device didn’t create a self-sustaining chain reaction, and was judged to have a blast equivalent to 600 tons of TNT, or .6 kilotons.

Comparing seismic data from 2006 and the new explosion have led experts to estimate that Monday’s test had a blast equivalent to around 4 kilotons. While that’s considerably more powerful than the 2006 test, experts note that it’s still well below the power of bombs tested by other nations like India and Pakistan, and also well below the power of the bomb dropped on Hiroshima in 1945, which had an explosive yields of 15 kilotons. “Was it another fizzle?” asked Hans M. Kristensen, a nuclear expert at the Federation of American Scientists. “We’ll have to wait for more analysis of the seismic data, but so far the early news media reports about a ‘Hiroshima-size’ nuclear explosion seem to be overblown” [The New York Times].

Seismologist Paul Richards also says it’s unlikely that the blast came from conventional explosives. “To me, a chemical explosion on the order of a few thousand tonnes, with all the stuff detonated at all the same instant, is not a credible scenario,” he says [Nature News]. To confirm this assessment, experts will look for traces of radiation drifting from the site; in particular, they’ll scout for radioactive xenon isotopes in ratios that are distinct from those released by other sources, such as nuclear power stations [Nature News]. The U.S. Air Force may have already launched an aircraft with specialized “sniffer” devices that can detect radiation carried on the wind, and ground-based radionuclide monitoring stations in Japan and Russia may have their first results in a matter of days.

Related Content:
80beats: Despite All Evidence, North Korea Claims a Successful Satellite Launch
80beats: North Korea’s Planned Satellite Launch Sounds More Like a Missile Test

Image: U.S. Geological Survey

CATEGORIZED UNDER: Environment, Technology
  • mandy marten

    wow. see how technology has gotten better and helps us!!! yay! We americans or anyone here in america should be very proud of their enormous contributions toward science. we might be in bad times but we should never forget how great our country is and what it has done for us and what it will do for us.

  • Grant H

    This situation has me very worried. I’m concerned for the safety of South Korea, particularly Seoul.

  • Uncle B

    Fission for power or weapons must be stopped at all costs, everywhere! Outside a “Nuclear Holocaust” of course! In America we still depend on Nuclear Fission for Electricity and this must come to an end! We are contaminated with a poison, so terrible, and waste from a foolish activity, as to threaten all life on the Earth forever! In light of the notion that Solar Power, Wind Power and Wave Power combined, can overwhelm us with electricity easily, it seems foolhardy to listen to the call of the Corporatist, who insists better “ROI”, his God, for Nuclear adventures, and rules America with an Iron fist at the moment! Dumbed down Americans, with high school educations rife with the government propagandists Horse-Shiite, and football and illicit under-age sex in their hearts, hardly can perform grade school level tasks from China, and then, only in one language! not like bilingual Canadians! These people, with really no developed cognitive powers, rule the “Free World” with their votes? Sometimes I am glad that the only votes that really count in Corporate America are the votes of shareholders, safer that way to be sure! Let the “Sham” continue, Let the War-Games begin! The military industrial complex cannot survive without war, and the people need jobs, so let them build the cannons, then, be the fodder! A win-win for all! All investors that is! ROI is king! “Fiat” the dollar for profits forever! Except for Mother Nature, who has suffered terrible wounds at the hands of the American Military, and will not be able to continue to provide top-soil, water, clean spots on earth for human habitation forever, not even in North Korea! We are at a stalemate! Mankind, struggling in his own night- terrors, fighting to survive, dying to survive, like fvcking for virginities sake! The final solution? Insanity! Kim Jong Ill, You are a madman, You know your life is limited, don’t take all of us with you! Die like a man! on your own, as we all do! now go away you short fvck, and let the rest of us be! Can’t someone assassinate this asshvle? Where’s the gun-happy Jew, Massade and all! We need a hero! Fast! Wolf Blitzer, can you help us? Please!

  • Angry

    People with absolutely no idea about Nuclear power have to be stopped at all costs. Excuse me, idiot, but all the nuclear waste in the US from DAY ONE would fit in 50-gal drums on a football field. ONE football field, ONE layer.

    It’s stupid people like you who make it difficult for real scientists to do anything that will alleviate our energy dependence on fossil fuels. Did I mention that I think you are an idiot?

    [Moderator’s note: This comment has been edited for profanity.]

  • Don

    Yeah, but that is 1 football field sized waste for thousands of years.

    What are you going to do with all that radioactive waste?

  • Vince Ligons

    The US is already at war with N. Korea and has been so for nearly 60 years. RepuboDems are way too late to start a war with Korea. Truman (a DemoPub) took care of that back in 1951 or 2.


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