Major Taiwanese news group Eastern Media International recently reported, based on sources from North Korea, South Korea, and Japan that North Korea’s Punggye-ri Nuclear Test Site suffered a major mountain structural change. This resulted in large-scale collapses of the underground tunnels for nuclear tests. North Korea completed its sixth nuclear test on September 3. A collapse occurred around September 10 burying around 100 workers. During the rescue mission, a second collapse took the lives of roughly another 100, mainly rescue staff. South Korean officials thought that, after the last test, the nuclear site had a big hole, the size of around 100 meters. If North Korea conducts more nuclear tests under the current conditions, serious radioactive leaks may occur. Three small scale earthquakes occurred after the last nuclear test. Scientists expressed the belief that structural collapses caused those quakes.
Sources: Eastern Media International, October 31, 2017
https://www.ettoday.net/news/20171031/1042620.htm