On 12 February 2013, North Korean state media announced it had conducted an underground nuclear test, its third in seven years. A tremor that exhibited a nuclear bomb signature with an initial magnitude 4.9 (later revised to 5.1) was detected by The China Earthquake Networks Center, Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission and the United States Geological Survey. In response, Japan summoned an emergency United Nations meeting for 12 February and South Korea raised its military alert status. It is not known if the explosion was nuclear, or a conventional explosion designed to mimic a nuclear blast; as of two days after the blast, Chinese, Japanese, and South Korean investigators had failed to detect any radiation.