Provocation or real threat? North Korea claims hydrogen bomb test (part 2)

Did North Korea really just blow up a hydrogen bomb? The claim on state television comes after a 5.1-magnitude earthquake that has all the trimmings of past underground nuclear testing - testing that's in clear violation of United Nations resolutions. There's strong condemnation not only from traditional foes in Seoul, Tokyo and Washington, but also neighbouring China, where the tremour was felt. So how volatile is the situation on the Korean peninsula?