 By LEE BOWMAN Scripps Howard News Service October 09, 2006
More than 325 monitoring stations report 10 billion bits of data each day in a system designed to give almost instant notice of a possible nuclear device explosion like the underground test carried out by North Korea. The sensors - the world's largest scientific watchdog - detect seismic, hydroacoustic and acoustic pressure, and are maintained under the Preparatory Commission of the International Comprehensive Nuclear Test Ban Treaty, and the data collected at the International Data Center in Vienna, Austria.
The treaty banning all nuclear explosions has not been ratified by the requisite 44 nations that possess nuclear power or nuclear research reactors, but the monitoring network is in place and supported by governments that have signed the treaty. The United States has signed the treaty and stopped all nuclear tests, but has not ratified the agreement. Earthquakes and underground detonations of large amounts of conventional explosives also produce tremors that can register about magnitude 4.0 on the seismic scale - about the magnitude reported from northeastern North Korea - but seismograms from atomic explosions have a signature different than those of other sources. The network picks up roughly 50,000 earthquakes a year, and all must be analyzed through supercomputers to determine if the origin is natural or man-made, a process that can take days to complete. Gauging the size of an underground nuclear detonation, particularly a small one, is often difficult. The energy transferred through the Earth's crust can vary depending on if the subsurface is rocky - as it is in North Korea - or soft, and on other factors, such as if the bomb's makers can stage or "decouple" the nuclear blast in a way that downplays its power. Initial estimates - from military and intelligence sources throughout the region - of the size of Sunday's explosion ranged from a blast equivalent to about 500 tons of TNT, to as much as 15,000 tons. The high estimate, from Russian defense officials, would make the North Korean bomb equal in destructive power to the atomic bomb the United States dropped on Hiroshima, Japan, in 1945 during World War II. Scientists concede the monitoring system might not detect a very small underground nuclear test carried out in just the right circumstances. "Remember, the CTBT does not ban the bomb, it bans the bang," said Peter Marshall, a British seismologist who specializes in the detection of waves from weapons blasts and an advisor to the treaty organization. Officials at the International Data Center note that while 50 seismic stations automatically report to the network, it takes longer to get reports from some of the 120 auxiliary stations that only feed reports upon specific request. Until the treaty is ratified, none of the data collected through the network can be made public, but it is shared with governments and authorized organizations. "Within 72 hours we will have full data. Then all our information will be available to member states,'' said Lassina Zerbo, director of the Data Center. The test ban treaty stations for detecting sound waves are intended mainly to monitor aboveground or underwater nuclear explosions, although they can give some limited aid in tracing underground blasts, too. The final part of the CTBT network is 80 air-sampling devices capable of detecting minute levels of radioactive particles. Initial results from monitors in Japan, Russia and South Korea did not detect any immediate changes in radiation levels, but experts say immediate release of such material from an underground test is rare. Satellite and other intelligence sources had strong indications that North Korean workers were preparing at least one shaft estimated at about 2,000 feet deep for a test in recent weeks, including backfilling and sealing the tunnel. It's possible to contain an underground nuclear blast so that no radiation is released to the surface, but leaks are common. Nuclear watchdog groups estimate about a fifth of the underground tests carried out by the former Soviet Union resulted in surface releases, as did several such tests in the U.S. before live testing of nuclear devices was suspended a decade ago. So, in coming days and weeks, scientists operating the radiation monitors will watch for any telltale increases in levels of the radioactive particles Xenon-133 and Argon-37, which are most likely to seep out of the ground near a test site through tiny cracks in the rock.
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