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North Korea's apparent nuclear test had an explosive yield of between six and seven kilotons, South Korea's defence ministry said, revising its earlier estimate of 10 kilotons or more. AFP/Getty Images

The same sensors that routinely scour the planet for telltale signs of nuclear weapons tests, such as the one North Korea conducted this week, can be used to track whales, monitor air pollution and forewarn of tsunamis, among other science projects.

"The concept of connecting arms control monitoring to environmental monitoring has been emerging in the community of specialists who think about this for a while," geophysicist Raymond Jeanloz, with the University of California Berkeley, told Discovery News.

Since the mid-1990s, a United Nations-backed organization has monitored compliance to the Comprehensive Nuclear Test Ban Treaty with a worldwide network of seismometers, radiation detectors and acoustic sensors on land and in the oceans.

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The treaty, which prohibits nuclear explosions for any purpose, has been ratified by 159 countries. Another 24, including the United States, have signed the agreement, but not ratified it.

The network, which currently consists of 337 facilities around the world, is not the only one that keeps tabs on the planet’s land, oceans and atmosphere for evidence of nuclear explosions by monitoring sound waves and analyzing air samples.

The  2004 Indian Ocean earthquake and tsunami proved a key event for demonstrating the systems’ other potential applications.

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"In hindsight, they realized that they had recorded the tsunami as it went across the Indian Ocean rapidly enough and reliably enough that they could have in principle sent out warnings if there had been a system for providing that and potentially might have saved thousands of lives," Jeanloz said.

Six years later, radiation detectors installed for arms control monitoring tracked fallout from the Fukushima nuclear power plant in Japan following another earthquake.

"We should be thinking about arms control more generally, whether it’s trying to account for warheads stored in various arsenals, tracking the proliferation of nuclear materials, even possible tracking of biological weapons, capabilities and materials," Jeanloz said.

"One might view all these things are being, to varying degrees, linked to the monitoring of the environment which we would like to monitor for pollution, for health and other reasons," he said.

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Using the technology for scientific purposes also would buttress the network’s prime use.

"We have this infrastructure with lots of sophisticated equipment and these technical people sitting around waiting and listening and looking -- hopefully for nothing. After a while, it’s hard to keep people motivated and they move on to other fields," Jeanloz said.

"There are all these systems out there that could be very useful," added Brian Weeden, technical advisor with the Secure World Foundation.

Some of the spinoff applications could help weapons monitoring as well, such as sensors that detect low-frequency sounds being used to track rocket launches.

"There’s a whole lot of information out there. Even other systems that are not designed with verification as their intent could be useful," Weeden said.

Jeanloz’s paper is published in this week’s Science.