Was North Korea's test nuclear?

Was it nuclear or just a lot of conventional bombs? Scientists say that it could take days before they can confirm North Korea's claim that it has carried out a nuclear test. From MSNBC:

Like earthquakes, large explosions send out shockwaves that can be detected on seismographs. 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.

He likened the problem to trying to "detect the violins or a flute in a symphony orchestra when you are playing the cymbals."

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.