The quake had a depth of ten kilometers, the U.S. Geological Survey said, while Chinese earthquake networks put it at zero [surface level]. A 4.9-magnitude earthquake in a similar location was recorded before confirmation of North Korea’s third nuclear test in 2013 at the site.

Officials in Seoul are checking the details of the earthquake with the meteorological office, a government official said. The government is convening an emergency meeting, according to the official Yonhap news agency.

 North Korea may be preparing to test thermonuclear weapons capabilities at its Punggye-ri nuclear test site, Yonhap News reported earlier this month.

The earthquake follows North Korea’s threat in September that it is ready to use atomic weapons against the U.S. at any time and that its main nuclear facility was fully operational. The regime in Pyongyang has often launched missiles or conducted nuclear tests to raise tensions as it seeks economic and political concessions from South Korea and the U.S.