North Korea’s underground nuclear tests may have affected the Earth’s crust around the test site for years after the explosions ended. A new study has found that 1,399 local earthquakes occurred near Mount Mantap between 2008 and 2025, with seismic activity increasing even years after North Korea conducted its final nuclear test.
The findings suggest that repeated underground nuclear explosions may have disturbed the surrounding rocks and reactivated previously quiet faults, causing earthquakes long after the tests were over.
Six nuclear tests under Mount Mantap
North Korea conducted six underground nuclear tests at the Punggye-ri nuclear test site beneath Mount Mantap between 2006 and 2017. The final test, carried out in September 2017, was the largest of the six. The US Geological Survey recorded the resulting seismic event at magnitude 6.3, while researchers estimated the explosion’s yield at between 100 and 250 kilotons.
Satellite radar images also showed significant changes and deformation near the summit of Mount Mantap following the explosion. Until now, much of the research on the site had focused on identifying the timing, location and strength of North Korea’s nuclear tests. The longer-term effects on the surrounding earthquake activity were less clearly understood.
Researchers identify unusual earthquake activity
To study the issue, researchers led by Xingli Fan examined seismic data from monitoring stations in China and South Korea. Some of these stations were located between 80 and 200 kilometres from Mount Mantap.
Their analysis identified 1,399 local earthquakes from 2008 to 2025, a significantly higher number than earlier earthquake records had shown.
Researchers noticed an unusual pattern after the 2017 nuclear test. Normally, earthquakes triggered by an explosion are expected to decrease over time. But around Mount Mantap, seismic activity began to increase about three weeks after the 2017 explosion.
The earthquakes continued to become more frequent and stronger through 2025.
Faults may have been reactivated
High-precision analysis showed that many of the earthquakes occurred along two fault structures running roughly north-northwest.
According to the researchers, this pattern suggests that the earthquakes were not simply random events. Instead, the nuclear explosions may have changed the stress conditions inside the Earth’s crust and reactivated faults that had previously remained quiet.
The researchers believe that repeated nuclear explosions gradually damaged the shallow layers of the crust. This could have changed the pressure and stress around existing faults, allowing some of them to become active over a period of several years.
Long-term impact of underground nuclear tests
The study suggests that the effects of an underground nuclear explosion may not end when the blast is over. Repeated tests could leave a long-lasting seismic footprint, potentially changing the behaviour of faults and triggering earthquakes years later.
The findings could also help scientists better understand and monitor former nuclear test sites, particularly when trying to distinguish earthquakes caused or influenced by past explosions from naturally occurring tectonic activity.
