Chris from Highly Allochthonous -- say that five times fast -- has a great post summarizing the geological issues of the North Korean nuclear test (how deep? how do we know that? etc.) Check it out.
The fine folks at the Discovery Institute claim that differentiation between nuclear tests and natural tectonic activity contistutes use of a Design Inference. (Caution: the discussion involves Casey Luskin. Protect your brain cells first with a healthy dose of ethanol)