North Korea’s nuclear tests may have triggered a rise in earthquakes around its main nuclear test site, with the activity continuing for years after the country’s last test in 2017. Moreover, the frequency and strength of these earthquakes are increasing over time, a new study has found. 

While Mount Mantap and its surrounding area had been quiet for the past 2,000 years and there had been no earthquakes, scientists looked at seismic data from 2008 to 2025 and detected 1,399 earthquakes around the mount, where North Korea carried out six underground nuclear tests between 2006 and 2017.

The findings are unusual because earthquakes linked to nuclear explosions generally do not continue to increase for years after a test.

The first earthquake recorded in the area came in 2013, after North Korea’s third nuclear test. But there were very few quakes in the following years.

That changed after the country carried out its sixth and largest nuclear test in 2017.

The study authors said seismicity, which refers to the frequency and strength of earthquakes, “remained sparse until 2017, when activity increased markedly after the sixth and largest detonation.”

The 2017 test produced a magnitude 6.3 earthquake. It may also have caused a tunnel collapse and changed the shape of the mountaintop by around 3 metres.

The earthquakes recorded after the tests were not particularly strong.

Kim, a professor in the Department of Geological Sciences at Pusan National University, told CNN that most of them had magnitudes between 2 and 3. They also appeared to have happened at shallow depths.

The area was also known to have very little seismic activity before North Korea began its nuclear tests.

“We have more than 2,000 years of historical record in China and Korea. We have one event about 100 kilometers away,” Kim said. “I cannot say there’s no earthquakes, but the seismic activity here is very low.”

Researchers believe the rise in earthquakes could mean that the ground beneath Mount Mantap did not return to its earlier state after the 2017 explosion.

Instead, at least two existing faults may have become active following the test, Kim said.

The blast has reactivated old, dormant cracks within the mountain. Furthermore, new cracks in the rocks created by the explosion have filled with water. This pore pressure is causing the rocks to slide together, and a series of small earthquakes are occurring.