A hydrogen bomb is more powerful than an atomic bomb because it employs a two-stage nuclear reaction to boost its explosive power. The first stage is a nuclear fission reaction (such as in a traditional atomic bomb), which then triggers a secondary nuclear hydrogen fusion reaction that gives the hydrogen bomb its greater explosive yield.
If this detonation was a hydrogen bomb test – which the US government is disputing – then it was likely less successful than the North Korean leadership may have hoped. A hydrogen bomb would be expected to register an explosive yield 100 to 1000 times larger than a fission bomb. However, the blast does not appear to have registered a sufficient explosive yield to constitute a successful hydrogen bomb test.
The tested device may have been a "boosted fission weapon", a precursor technological step to a hydrogen bomb. Even so, the explosive yield would be expected to be five to ten times larger than that registered by this test.
Alternatively, the device may have been a test of the first-stage fission "trigger" of a two-stage hydrogen bomb. This is plausible. This test is estimated to have been approximately 1.5 times as powerful as the 2013 nuclear test, based on the blast's seismic readings.
All of these possibilities are consistent with the developmental trajectory of North Korea's nuclear weapons program. The miniaturisation of a nuclear weapon for deployment on the warhead of a ballistic missile remains North Korea's primary technical obstacle to a fully operational nuclear weapon capability.
Regardless of its relative success from a technical standpoint, the emphasis of this test on hydrogen bomb development is significant – a hydrogen bomb can be more easily miniaturised.
Fitting the pattern
The technical development of North Korea's nuclear program is a dynamic space. But the contours of Korean Peninsula nuclear politics have remained relatively predictable for many years. There is a pattern that has emerged since North Korea's first nuclear test in 2006.
First, North Korea tests a nuclear device. The test highlights its advancements in nuclear weapons technology without conclusively demonstrating a deployable weapon.
It is clear the North Korean government sees great intrinsic value in nuclear weapons as a strategic deterrent against external aggression and an umbrella for economic development. In addition, the threat of nuclear weapons is useful as a diplomatic bargaining chip, a vehicle for bureaucratic interests and a rallying symbol of the country's hyper-nationalist ideology.
Second, the international community responds with rhetorical indignation and resolve. That resolve rapidly dissolves into a negotiated compromise resolution from the UN Security Council that adds an additional layer to the ineffective economic sanctions regime against the North Korean government.
The South Korean capital, Seoul, is essentially indefensible against North Korean rockets and artillery due to its close proximity to the demilitarised zone. Given the potential impact of war in Korea, with estimated casualties of up to 500,000 people and a cost of more than US$1 trillion, the risk is too high to justify the desired gain.
So, for any rational military strategist, the risks of an armed response to North Korea's sanctions violations and pin-prick provocations are prohibitive.
This leaves non-military measures such as economic sanctions as the default response available to the Security Council in responding to North Korea's nuclear tests. The international economic sanctions regime against North Korea was instituted through Security Council Resolution 1718 in October 2006 after its first nuclear test, and was added to in resolutions 1874 and 2094 following the 2009 and 2013 nuclear tests.
The Chinese government has often cited strategic reasons for treading gently with sanctions enforcement. North Korea, as China's ally in the northeast, forms a key component of a series of buffer zones surrounding China's territorial periphery. China fears the potential for economic and social dislocation in its northeastern provinces caused by large refugee flows from North Korea in the event of war or state collapse.
Third, North Korea finds creative means of circumventing the sanctions regime and continues its nuclear weapons development. To comply with the Security Council's sanctions regime, North Korea would have to abandon not only its strategic deterrent but also the foundation of its medium-term economic development strategy, the pillar of its institutional governance structure, and its associated ideological and propaganda commitments.
Gains from the lifting of sanctions and the relative trinkets offered in grand bargain proposals would make for an unfair exchange for denuclearisation in the eyes of the North Korean leadership.
It is likely that the response of regional countries and the Security Council over the coming days will remain true to form in composing a new resolution with little more than a list of new individual and institutional targets for sanctions in North Korea.
In the meantime, North Korea remains committed to perfecting a deployable nuclear weapon capability. It is confident in the understanding that there appears little the international community can do to prevent it.
This article first appeared in The Conversation
Media; Catherine Garrett 9479 6565 / 0418 964 325
Image credit; Reuters/Kim Hong-Ji