North Korea expert Jeffrey Lewis said Saturday on the website 38 North that the main question about Pyongyang's threat to conduct a fourth nuclear test is not what but how the test will be carried out.
He highlighted North Korea's response to the UN Security Council's condemnation of its ballistic missile launches last week, when Pyongyang said it will bolster its nuclear deterrence with a new kind of nuclear test.
Lewis said he believes the test will be conducted with simultaneous detonation of other nuclear devices.
He pointed out that Russia and the U.S. have conducted simultaneous detonations of up to five nuclear bombs, and compared the North's current situation to that of the Soviet Union.
Like the Soviet Union, Pyongyang lacks nuclear facilities, suffers financial issues and has to deal with unpredictable weather.
He also pointed to the possibility of vertical tunnel testing.
The current test site at Punggye-ri has horizontal tunnels in the mountains near the site, but the size of the bombs Pyongyang can test is limited by the size of the mountains and the resulting overburden, and he said the test site could only accommodate few tens of kilotons.
He pointed out that larger tests would need to be done in tunnels drilled much deeper into the ground.
He also suggested that atmospheric and thermonuclear tests are a possibility.
Atmospheric nuclear tests are prohibited under the Limited Test Ban and the Comprehensive Nuclear Test Ban Treaties but North Korea has neglected to sign both.
Lewis says Pyongyang is unlikely to conduct an atmospheric test, as it would anger the Chinese public.
North Korea has conducted three nuclear tests so far -- in 2006, 2009 and February of 2013.
Kim Hyun-bin, Arirang News.