A magnitude 5.9 earthquake off North Korea early Thursday jolted watchers of the country's weapons development but experts say it was not caused by a nuclear test.
Analysts say North Korea needs to conduct another atomic test explosion to perfect a nuclear-tipped missile capable of reaching the continental U.S. On July 4, Pyongyang test-launched its first intercontinental ballistic missile. 4. North Korea's five previous nuclear tests caused signs of artificial quakes.
Here's what experts say about the quake: