The US Geological Survey (USGS) detected a 2.9-magnitude natural disaster in area close to North Korea's nuclear test site on Thursday evening, but is now unable to explain the nature of the seismic event.
"The depth is poorly constrained and has been held to 5 km by the seismologist".
It was the latest in a string of aftershocks following North Korea's sixth nuclear test on September 3, which caused a 6.3 magnitude natural disaster, according to the USGS.
Prior to North Korea's nuclear test in early September, the DPRK previously conducted nuclear tests in 2006, 2009, 2013, and two in 2016, with explosive yields of less than one kiloton, 2-4 kilotons, 6-9 kilotons, 7-10 kilotons, and 20-30 kilotons, respectively.
A 3.4 magnitude quake last month near the same location sparked fears there could have been another nuclear test.
The blast was large enough that residents in China, some 125 miles away, felt the ground shake beneath them.
There are no nearby tectonic plate faultline boundaries to the test site. "If Pyongyang goes ahead with another test in the area, it could risk radioactive pollution". "The recent small quakes suggest that the test might have triggered crust deformation". This second tunnel may have caved in after the sixth test, the intelligence officials said. Foreign Minister Ri Yong Ho said last month the North could test "an unprecedented scale hydrogen bomb" over the Pacific Ocean, in response to U.S. President Donald Trump's threat to "totally destroy" the country.