A small earthquake has been detected early Friday near North Korea's nuclear test site, the U.S. Geological Survey said.

The 2.9 magnitude temblor was detected about 23 kilometers (14 miles) from Sungibaegam, “in the area of previous North Korean nuclear tests,” USGS said. Officials at South Korea’s Korea Meteorological Administration said it wasn’t man-made and didn’t appear to cause any damage in the area.

The temblor is the fourth since North Korea’s sixth and most powerful nuclear test explosion Sept. 3. Some experts suggested the area is now too unstable to conduct more bomb tests. That test caused a 6.3 magnitude earthquake, according to the USGS.

The South Korean officials, who requested anonymity citing department rules, said they believe the four quakes probably happened because the underground nuclear test last month weakened or affected the tectonic plate structures in the area. The region isn’t one where earthquakes naturally occur and no quakes were detected after the five smaller nuclear tests North Korea has conducted since 2006.



The officials declined to say how the recent quakes might have affected the area and the test site, where all of North Korea’s nuclear bomb tests have taken place. But some civilian experts said North Korea may stop using the site.

