A magnitude 5(point)9 earthquake off North Korea today jolted watchers of the country's weapons development but experts say it was not caused by a nuclear test. <br/><br/>Analysts say North Korea needs to conduct another atomic test explosion to perfect a nuclear-tipped missile capable of reaching the continental US.<br/><br/>On the 4th of this month, Pyongyang test-launched its first intercontinental ballistic missile. North Korea's five previous nuclear tests caused signs of artificial quakes.<br/><br/>According to the US Geological Survey, the quake struck 187 kilometers southeast of the northern port city of Chongjin. The epicenter was 559 kilometers below the seabed.<br/><br/>South Korea's Defence Ministry said there was no indication that North Korea had carried out a nuclear test.<br/>