They did it - or - did they?

Last evening's post:

Congratulations to the North Koreans, who appear to have successfully detonated a nuclear weapon, if the Magnitude 4.2 earthquake measured by the USGS is a reasonable indication of such a test.

As I've considered the "nuclear test", something rubs me wrong. I have researched the manner in which such devices are tested and it occurs to me that based on the relatively low magnitude of the tremor indicated by the USGS, and the fact this was an underground test, there is yet no way to classify this as a fission explosion. It well could be a mere 1000+ tons of conventional high explosive detonated below ground to produce an effect almost identical to that of a nuclear explosion. It would not be beyond the North Koreans to be bluffing this way.

But even so - even if it were nuclear - as I mentioned to my father in law this morning, any nuclear material exploded on their own territory is that much less that can be exported to other lands. Let them explode them all on North Korean soil.