Experts: Latest North Korea earthquake a sign of instability at nuclear test site

“The explosion from the Sept. 3 test had such power that the existing tunnels within the underground testing site might have caved in,” said Kim So-gu, head researcher at the Korea Seismological Institute.

“I think the Punggye-ri region is now pretty saturated. If it goes ahead with another test in this area, it could risk radioactive pollution.”