2017 North Korean nuclear test

North Korea conducted its sixth nuclear test on 3 September 2017, stating it had tested a thermonuclear weapon (hydrogen bomb).

The United States Geological Survey reported an earthquake of 6.3-magnitude not far from North Korea's Punggye-ri nuclear test site. South Korean authorities said the earthquake seemed to be artificial, consistent with a nuclear test. The USGS, as well as China Earthquake Networks Center, reported that the initial event was followed by a second, smaller, earthquake at the site, several minutes later, which was characterized as a collapse of the cavity.

Nuclear device
The North Korean government said it has detonated a hydrogen bomb that could be loaded onto an intercontinental ballistic missile (ICBM). The announcement stated the warhead had a variable yield "the explosive power of which is adjustable from tens kiloton to hundreds kiloton ... which can be detonated even at high altitudes for super-powerful EMP attack". A later technical announcement called the device a "two-stage thermo-nuclear weapon" and stated experimental measurements were fully compatible with the design specification, and there had been no leakage of radioactive materials from the underground nuclear test.

Photographs of North Korean leader Kim Jong-un inspecting a device resembling a thermonuclear weapon warhead were released a few hours before the test.

Jane's Information Group estimates North Korean thermonuclear/hydrogen Teller-Ulam type bomb to weigh between 250 and 360 kilograms (~550 - 790 lbs.).

Yield estimates
On the day of the test the chief of the South Korean parliament's defense committee, Kim Young-Woo, stated the nuclear yield was equivalent to about 100 kilotons of TNT (100 kt): "The North's latest test is estimated to have a yield of up to 100 kilotons, though it is a provisional report." The independent seismic monitoring agency NORSAR estimated that the blast had a yield of about 120 kilotons, based on a seismic magnitude of 5.8.

On 4 September, the academics from the University of Science and Technology of China released their findings based on seismic results and concluded that the nuclear test occurred at 41.2982°N, 129.0742°W at 03:30 UTC, only a few hundred meters from the four previous tests (2009, 2013, January 2016 and September 2016) with the estimated yield at 108.1 ± 48.1 kt.

On 5 September, the Japanese government gave a yield estimate of about 160 kilotons, based on analysing Comprehensive Nuclear-Test-Ban Treaty Organization seismic data, replacing an early estimate of 70 kilotons.

On 6 September, an early assessment by U.S. Intelligence that the yield was 140 kilotons, with an undisclosed margin of error, was reported. On 13 September, U.S. Intelligence was reported referring to an early yield estimate range of 70 to 280 kilotons made by the Air Force Technical Applications Center.

On 12 September, NORSAR revised its estimate of the earthquake magnitude upward to 6.1, matching that of the CTBTO, but less powerful than the USGS estimate of 6.3. Its yield estimate was revised to 250 kilotons, while noting the estimate had some uncertainty and an undisclosed margin of error.

On 13 September, an analysis of before and after synthetic-aperture radar satellite imagery of the test site was published suggesting the test occurred under 900 m of rock and the yield "could have been in excess of 300 kilotons".

Reactions
The United Nations Security Council met in an open emergency meeting on 4 September 2017, at the request of the US, South Korea, Japan, France and the UK.

Canada, China, Indonesia, Japan, Malaysia, the Philippines, Russia, Singapore, South Korea, and the United States voiced strong criticism of the nuclear test.

US President Donald Trump wrote on Twitter: "North Korea has conducted a major nuclear test. Their words and actions continue to be very hostile and dangerous to the United States". Trump was asked whether the U.S. would attack North Korea and replied: "We'll see." Defense Secretary James Mattis warned North Korea that it would be met with a "massive military response" if it threatened the United States or its allies.