▲ An image indicating areas where earthquakes occurred near North Korea's nuclear test site in Punggye-ri, provided by Pusan National University (PHOTO NOT FOR SALE) (Yonhap)

SEOUL, Sept. 18 (Yonhap) -- Unexpected, prolonged seismic activity has been detected around North Korea's Punggye-ri nuclear test site, notably after the regime's final and most powerful test in 2017, scientific experts said Friday.

The latest findings were discovered by a joint research team from South Korea's Pusan National University and China's Chengdu University of Technology and published in Science, a prominent academic journal.

According to an analysis of seismic wave data analyzed over the past 17 years from 2008, researchers detected a sudden rise in the number of earthquakes near the areas around the Mantap mountain, where the North detonated a total of six nuclear devices at underground tunnels from 2006 to 2017.

During the 11-year period, researchers detected some 60 earthquakes occurred after the North's first nuclear test conducted in 2006. Such seismic activities appeared to have occurred more frequently around 2013, following the North's third nuclear test, the researchers said.

Notably, tremors intensified following the North's largest and final nuclear test in 2017. A total of 1,330 earthquakes have followed since, concentrating on a fault zone spanning some 24 kilometers wide, researchers found. Although earthquakes that followed previous nuclear tests were mostly short-lived, those that erupted after the 2017 test intensified in both frequency and magnitude throughout 2025, they added.

Professor Kim Kwang-hee, who led the South Korean research team, warned that North Korea could experience an earthquake as strong as 6.4 magnitude should the fault zone where previous quakes were concentrated become active.

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