Professor Alan Douglas from AWE Blacknest worked on the study

Scientists believe they will soon have a network of "listening" stations in place that will make it virtually impossible for a nuclear device to be detonated without anyone knowing.

Analysis of the shock waves from a controlled underground test last year has led seismologists to believe they can detect even the smallest of bomb explosions.

The research, published in the journal Nature, is promoted as an encouraging demonstration of the International Monitoring System (IMS) now being set up to verify the Comprehensive Nuclear-Test-Ban Treaty (CNTBT).

The IMS will eventually have 321 stations around the world, constantly watching the air, sea and land for signs of nuclear explosions.

Kazakhstan experiment

Last August's experimental explosion involved the detonation of just 0.1 kilotonnes of conventional explosives at Degelen mountain in Kazakhstan.

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The seismic waves generated by the blast have been analysed by researchers at AWE Blacknest, which is part of the UK's Atomic Weapons Establishment at Aldermaston.

They specialise in trying to distinguish the seismic signals generated by underground nuclear explosions from those generated by earthquakes.

The scientists say the waves from the experimental detonation were detected as far away as Virginia in the US, and in central Australia.

The absence of detectable surface waves at a station in the Russian Federation, very much closer to the epicentre of the blast, indicated that the explosion could not have been an earthquake, the researchers say.

Other results suggest to the scientists that the IMS, when fully operational, will be able to show that "explosions with yields well below one kilotonne can be recognised as suspicious."

Cautious optimism

However, the research team does strike a note of caution. Successful detection may depend on a number of factors, they say, such as the geological situation of the test site. They make the point that any illicit tester may attempt to dampen the signal by, for example, exploding a device in a very large cavern.

Recent Asia tests have raised concern

They also acknowledge that knowing an event is going to take place makes interpretation easier.

"These results possibly overstate the ability of seismologists to identify small explosions," they write in Nature.

"Knowing when and where the explosion took place means the signals can be interpreted with more confidence than would be possible when analysing signs of a possible disturbance for which the only information is the seismograms."

The CNTBT will prohibit any nuclear weapon test or any other nuclear explosion anywhere in the world. The treaty requires the ratification of 44 nuclear-capable countries before it comes into force.