A small earthquake detected on Friday near North Korea’s underground nuclear weapon test facility is adding to speculation that the mountain above the site may have been destabilised by the series of megaton blasts conducted by Pyongyang.

North Korea’s underground nuclear weapon tests are usually detected by earthquake measuring instruments, including its sixth explosion and biggest to date on September 3.

Since the September blast, seismic tremors in the region, including the one on Friday, along with landslides is raising speculation the country may have caused the mountain above the test site to shift.

The United States Geological Survey measured the Friday quake at 2.9 magnitude at a depth of 5 kilometers.

The USGS said it couldn’t confirm if the temblor was the result of a weapons test, saying on its website that “the Air Force Technical Applications Center (AFTAC) is the sole organization in the U.S. federal government whose mission is to detect and report technical data from foreign nuclear explosions.”

 

The Korea Meteorological Administration in South Korea said Friday’s quake was a magnitude 2.7 with a depth of 3 km in North Hamgyong Province in North Korea, or near the Punggye-ri nuclear testing site, according to Reuters.

North Korea’s six nuclear tests have been carried out in this location in the northwest of the country. According to 38 North, a Washington-based group that monitors North Korea, satellites images have shown a series of landslides occurred around the test site last month.

These disturbances are more numerous and widespread than those seen after any of the North’s previous tests, 38 North has said.

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

“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.”