North Korea's nuclear test in May indicated that an international network of nuclear detonation sensors is becoming increasingly capable of detecting violations of the Comprehensive Nuclear Test Ban Treaty, said leaders of a study that surveyed more than 200 scientists worldwide on the monitoring project's technical underpinnings (see GSN, April 22).
The test detonation was registered at 61 of the network's 228 seismographic monitoring stations, up from the 22 sites that identified Pyongyang's first nuclear test in 2006, study organizers told a meeting sponsored last month by the American Association for the Advancement of Science and the Center for Strategic and International Studies.
The network, expected to eventually incorporate 337 monitoring sites, is already capable of detecting detonations as small as 10 tons of TNT and locating an explosion with an approximate 10-mile margin of error, according to experts at the meeting.
In a 2008 test of the system's sensitivity, a hydroacoustic monitor off of Chile detected the detonation of roughly 44 pounds of TNT in waters roughly 3,700 miles away, near the coast of Japan.
Increasing interest in entering the test ban treaty into force prompted last year's launch of the International Scientific Studies Project, the most thorough assessment to date of the monitoring network's accuracy, said Ola Dahlman, the Swedish seismologist leadingthe effort. The study is sponsored by the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization.
The study gathered scientific feedback on the system from "more than 200 posters from 60 countries and ... (with) a fairly even distribution among the different technologies," Dahlman said.
Addressing concerns that a nation could take measures to obscure a nuclear test from the sensors, Dahlman said: "What risks are you prepared to take if you’re going to cheat? Are you going to take 90 percent (probability) of being detected? Well, probably not. Are you prepared to run a 10 percent risk? Well, the difference is quite considerable. ... It’s almost an order of magnitude."
"Is the treaty verifiable? That is a decision that has to be taken" by individual countries "based on each state’s security needs," Dahlman said, sarying that 148 nations "have answered ‘yes,’ by signing and ratifying the treaty."
The pact must be ratified by 44 nations that possessed nuclear weapons or nuclear-weapon technology in 1996. Nine of those states remain holdouts.
"We’re in a pretty different place, from a scientific perspective, from where we were 10 years ago," said Benn Tannenbaum, associate program director of the AAAS Center for Science, Technology and Security Policy. "The question that remains to be answered is a political one, and that is: Is that sufficient?" (American Association for the Advancement of Science release, Aug. 10).