On Tuesday night, the US Geological Survey detected an unusual 5.1-magnitude tremor in North Korea, located in the northeast of the country — a part of the world not known for earthquakes but very close to the nuclear test site of Punggye-ri. This underground nuclear site has been the location of three previous nuclear tests in 2006, 2009, and 2013, so monitoring agencies suspected that a fourth one had just happened:
Hours after the tremors, the North Korean regime announced it had successfully carried out its first underground test of a hydrogen bomb — a weapon much more powerful than an atomic bomb. But many experts discounted these claims because they say the blast wasn't large enough for a hydrogen bomb, which would yield 20 megatons, versus the 6 kilotons estimated in the recent test.
Even if North Korea didn't detonate an H-bomb, the tremor could still be North Korea's fourth nuclear test, and the United Nations Security Council has condemned it as "a clear threat to international peace."
North Korea has been developing a missile program over the past few decades, which has grown from artillery rockets to short- and medium-range ballistic missiles. It's also trying to develop long-range missiles. According to experts, some of these missiles could have the capacity to carry nuclear warheads, but there are doubts that North Korea can develop a nuclear weapon small enough for that. Here's a summary of North Korea's current missile program:
In addition to all the missiles on the chart above, there are reports that North Korea may have test-fired a ballistic missile from a submarine in late December. And in May, North Korea said it had conducted a similar successful submarine launch. A submarine-launched missile would be a significant boost to Pyongyang arsenal because those missiles are very difficult to detect and have a bigger range than land-based ones.