North Korea appears to have conducted a sixth nuclear test shortly after noon local time on Sept. 3. Initial reports from South Korea say the quake connected to the test measured 5.6 on the Richter scale, larger than the last test, which measured a magnitude of 5.1. Subsequent reports from the U.S. Geological Survey agency said the blast reached a magnitude of 6.3, indicating a significant increase in yield from any of the North's previous nuclear tests. The test follows Pyongyang's claim that it had completed the miniaturization of a hydrogen bomb capable of being fitted to an intercontinental ballistic missile. North Korea has repeatedly claimed perfection of hydrogen bomb technology, producing weapons that employ a more powerful fusion reaction, as opposed to the usual fission reaction of North Korea's more primitive nuclear weapons.