Scientists Probe North Korea Nuke Test

Big nuclear bombs make big waves, with clear signatures that make them fairly easy to detect, analyze and confirm that they were caused by splitting atoms. But smaller blasts - as North Korea's appears to have been - are trickier to break down.

The natural sound of the Earth, with its constant seismic activity of tectonic plates grinding together, complicates the task of trying to determine whether a smaller blast was caused by conventional explosives or a nuclear device, said Xavier Clement of France's Atomic Energy Commission.

His agency estimated the North Korean blast at around 1 kiloton or less - equivalent to the explosive force of 1,000 tons of TNT. For a nuclear device, that would be so weak that the French defense minister suggested that "there could have been a failure" with the North Korean reported test.

The test ban treaty, which bans all nuclear explosions, will not enter into force until it has been ratified by 44 states who possess either nuclear power or research reactors. So far 34 have ratified it. Holdouts include the United States, China, India, Pakistan, Israel and North Korea.