North Korea claimed to have tested its miniaturised thermonuclear bomb on 6 January 2016. North Korea's first three nuclear tests (2006, 2009 and 2013) were relatively low yield and do not appear to have been of a thermonuclear weapon design. In 2013, the South Korean Defense Ministry speculated that North Korea may be trying to develop a "hydrogen bomb" and such a device may be North Korea's next weapons test. In January 2016, North Korea claimed to have successfully tested a hydrogen bomb, although only a magnitude 5.1 seismic event was detected at the time of the test, a similar magnitude to the 2013 test of a atomic bomb. These seismic recordings cast doubt upon North Korea's claim that a hydrogen bomb was tested and suggest it was a non-fusion nuclear test.