This isn't good. North Korea has reportedly conducted a nuclear test. Unusual seismic activity in the region was detected that indicated a nuclear bomb and South Korea has told a United Nations Security Council diplomat that North Korea performed a nuclear test.
A 4.9 magnitude earthquake was felt in North Korea with the epicenter supposedly near known North Korean nuclear test sites. Which means, the earthquake—which is unnatural to the region—was probably caused by North Korea detonating a nuke. This would be the third time North Korea has performed a nuclear test—the other times being in 2006 and 2009. The 2006 test brought a 3.9 magnitude earthquake while the 2009 nuclear test bumped the region with a 4.5 magnitude earthquake.
The Comprehensive Nuclear-Test Ban Treaty Organization put out this statement:
"Today our monitoring stations picked up evidence of an unusual seismic event in the Democratic People's Republic of Korea (DPRK). The event shows clear explosion-like characteristics and its location is roughly congruent with the 2006 and 2009 DPRK nuclear tests. For now, further data and analysis are necessary to establish what kind of event this is. If confirmed as a nuclear test, this act would constitute a clear threat to international peace and security, and challenges efforts made to strengthen global nuclear disarmament and non-proliferation, in particular by ending nuclear testing."
Reuters is reporting that the North Korean earthquake indicates a nuclear blast of six to seven kilotons, according to the South Korea defense ministry. It's unclear which method North Korea used to make its nuclear bomb. In the previous tests, North Korea was using reprocessed plutonium to fuel the nuke but in 2010, North Korea publicly showcased its process of making highly enriched uranium.
According to coordinates from the US Geological Survey, the earthquake was felt conveniently near a road that Google Maps has named Nuclear Test Road:
An emergency UN Security Council session will be held tomorrow at 9:00PM EST but it's not like they've been caught off guard. North Korea has been threatening to detonate a nuclear bomb ever since the UN Security Council penalized Pyongyang for shooting rockets into space. In fact, on January 24th North Korea's National Defense Commission stated that they would perform "a nuclear test of higher level". Even as recently as today, US officials were bracing for a nuclear test saying it "could come at any moment". Guess it did. [Reuters, ABC News, WSJ]
Update: Yonhap News reports that North Korea has confirmed that it conducted its third nuclear test. The test was done underground using a "miniaturized nuclear device with greater explosive force".