The mountain where North Korea has conducted all its nuclear tests frequently is at risk of collapsing and spreading a massive dose of radiation across the region, the South China Morning Post reported Tuesday quoting Chinese experts.
A research team at the University of Science and Technology of China in Hefei, Anhui Province analyzed shock waves caused by the blasts and concluded that five of the North's six nuclear tests were carried out in tunnels under the same mountain in Punggye-ri.
"Its leader, geophysicist Wen Lianxing, said that based on data collected by more than 100 earthquake monitoring centres in China, the margin of error was no more than 100 metres," the daily said.
Wang Naiyan, the former chairman of the China Nuclear Society, said, "Another test might cause the whole mountain to cave in on itself, leaving only a hole from which radiation could escape and drift across the region, including China."
Geologists believe that a second tremor some eight minutes after Sunday's nuclear test was caused by the cave-in of a tunnel there.
"If the bombs were planted at the bottom of vertically drilled tunnels, the explosion would do less damage," the paper said. "But vertical tunnels were difficult and expensive to build, and it was not easy to lay cables and sensors to collect data from the explosion."
"Much easier was to bore a horizontal tunnel into the heart of the mountain, but this increased the risk of blowing off the top."
Wen's team estimated that the explosive yield released in the latest nuclear test was about 108.3 kilotons of TNT, more than double the 50 kilotons estimated by the South Korean Defense Ministry.