South Korea and Japan reported seismic activity at 09:50 KST ( 00:50 UTC ) . The United States Geological Survey reported a magnitude 4.7 earthquake at a depth of zero and put the center of the tremor about northwest of Kimchaek and northeast of Pyongyang , within a few kilometres of the country 's 2006 nuclear test site . The Japan Meteorological Agency measured the seismic activity at magnitude 5.3 . The Korea Institute of Geoscience & Mineral Resources reported seismic activity in the same area but far stronger than in 2006
2006 nuclear test
2006 North Korean nuclear test
2009 North Korean nuclear test