A statement on the US Geological Survey website reads: “This event occurred in the area of the previous North Korean Nuclear tests”.

The epicenter of the seismic event is located approximately 25 km away from Sungjibaegam, a town close to the Punggye-ri nuclear test site, at the depth of five kilometers.

According to South Korea’s weather agency, a small quake was detected, on Friday (10/13/2017), near North’s nuclear test site, but unlike a nuclear-related quakes, the quake did not appeared to be a man-made one.

On Friday, China’s General Administration of Customs announced that China’s imports from North Korea fell 37.9 percent in September, the seventh successive monthly decline. A small quake on September 23 was thought to be an aftershock of the nuclear test earlier in the month. Late last month, a magnitude 3.4 quake was detected under Mount Mantap- and there have been further small aftershocks since North Korea’s sixth nuclear test in early September. “If it goes ahead with another test in this area, it could risk radioactive pollution”, he added. These disturbances are more numerous and widespread than seen after any of the North’s previous tests, 38 North said.

North Korea, which is accelerating its efforts to develop more powerful nuclear weapons and missiles, is unlikely to waste its limited nuclear materials by conducting tests that are weaker than its sixth.

“The reason why Punggye-ri has become North Korea’s nuclear testing field is because this area was considered stable and rarely saw tremors in the past”, said Hong Tae-kyung, a professor of earth system science at Yonsei University in Seoul.

Du Hyeogn Cha, a visiting scholar at Seoul’s Asan Institute for Policy Studies, previously expressed similar worries, saying he wondered whether North Korea would be able to carry out another nuclear test in the area.

“Right now we think the threat is manageable but over time, if it grows beyond where it is today, well, let’s hope that diplomacy works”, he said. Other experts said the quakes might have been caused by landslides or the collapsing of test structures such as tunnels.