[38North] Imagery from September 8 also shows a large tractor/trailer cargo truck in the South Portal Area for the first time, and mining carts and other equipment are present outside the West Portal. Such activity, coming shortly after the largest underground nuclear test conducted at Punggye-ri to date (via the North Portal), suggests that onsite work could now be changing focus to further prepare those other portals for future underground nuclear testing.Revised Magnitude Estimates Raise the Equivalent Yield to Approximately One Quarter of a Megaton
At the time of 38 North’s first report on the sixth nuclear test, the preliminary seismic magnitude estimates varied from 5.8, as published by both the CTBTO and NORSAR, to 6.3 by the United States Geological Survey (USGS). More recently, both the CTBTO and NORSAR have officially revised their estimates upward to 6.1. This revision is significant because, rather than providing an equivalent yield of about 120 kilotons derived from the lower magnitude estimates, the application of standard formula with appropriate constants shows that the yield can now be estimated to have been roughly 250 kilotons (one quarter megaton). This large explosive yield is also quite close to what 38 North had previously determined to be the maximum estimated containable yield for the Punggye-ri test site.