North Korea sets off an earthshaking explosion — and claims it was nuclear. Was it? For scientists, that was not a quick and easy question to answer.
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.