FOI considers, based on seismic data, that North Korea conducted a nuclear weapons test on 3 September.
The test was conducted at 5:30 am Swedish daylight-saving time, at the estimated position 41.3N, 129.1E, that is, in the same area as earlier tests in October 2006, May 2009, February 2013, January 2016, and September 2016. It is reasonable to assume that the test, as earlier, was conducted in a tunnel in the Mant’apsan massif, at Punggye-ri.
Based on measurements at FOI’s seismic station in Hagfors, the magnitude was approximately 6.1, approximately 6.5 times stronger than the test in September 2016. The estimated detonation strength lies between 100 and 200 kilotons, which is thus substantially higher than earlier tests and consistent with North Korea’s having taken a further step in its nuclear weapons development, compared with what had been previously observed.
Analysis of data from eventual early radionuclide emissions may result in additional information about the test. Apart from after the first test, in October 2006, neither any immediate nor early radionuclide emissions have been detected from the North Korean tests.