The U.S. Geological Service has detected a magnitude 6.2 seismic event just on the Russian side of the country's border with North Korea. The closest North Korean town, Aoji Ri, is only 25 miles miles from the epicenter, which is also very close to China. The event occurred at exactly two seconds after midnight, local time.
The event was almost certainly an earthquake, but it comes at an inauspicious moment: North Korea is severely ratcheting up its talk of nuclear war today, urging foreign embassies in Pyongyang to evacuate their staff. The move is ostensibly because war is imminent, although North Korea is known to often issue such alarms and provocations without actually following through. Still, seismic activity within North Korea is sometimes a sign of a nuclear weapons test.
The epicenter is far enough from the border, and thankfully not within North Korea itself, that the world can safely conclude that this was not a nuclear event. The danger, though, is that the region is already on high alert waiting for some expected provocation from North Korea, and North Korea itself may be wary of the possibility of a preemptive attack from South Korea or the U.S. Things are tense, and this sort of unexpected wild card is not necessarily helpful in calming everyone down.
According to the USGS, the epicenter was at 42.713° North, 131.105° East. It recorded the activity at a depth of 349.1 miles – way too far underground for a nuclear test and, hopefully, something that leaders in Seoul and Pyongyang will take as reassurance that this was just another Pacific Rim quake.