A small magnitude 2.9 "earthquake" has been detected near the Nuclear Test Site in North Korea.  According to the US Geological Survey, it has "earthquake-like characteristics" but only the US Air Force Technical Applications Center can determine if it was a nuclear test.

This quake was very much smaller than another recent test, and it seems possible today's event was actually JUST an earthquake.  But given North Korea's belligerant attitude concerning its unlawful nuclear weapons program, anything is possible.