North Korea’s underground nuclear tests at Mount Mantap appear to have activated dormant geological faults beneath the mountain, producing a sustained rise in earthquakes years after the last detonation, according to a study published 17 September in Science.
The research examined seismic wave data from 2008 to 2025 around the Punggye-ri nuclear test site in North Hamgyong province, where North Korea carried out six underground nuclear tests between 2006 and 2017. It found 1,399 earthquakes in the area over that period, with both the number and magnitude of events increasing over time.
Seismic activity was sparse until 2017, when it increased markedly after North Korea’s sixth and largest detonation. The final test had an estimated explosive yield of 160 kilotons and unleashed a magnitude 6.3 earthquake. It is also believed to have caused an on-site collapse, perhaps involving a tunnel.
Earthquakes following underground explosions commonly decline as the effects of the blast subside. At Mount Mantap, however, seismicity continued to grow for years after the 2017 test, the study said. The pattern points to continuing changes in the shallow rock beneath the site rather than a short-lived response to the explosion.
Before this century, the area had been tectonically quiet, with earthquakes virtually unknown. The researchers said repeated explosions likely allowed cracks and other damage to build up in the shallow crust, changing the stresses acting on faults that had previously remained inactive.
Kwang-Hee Kim, a seismologist involved in the study, said the underground tests had progressively disturbed and damaged surrounding rock. Those changes, he said, altered stresses on pre-existing faults.
The team suspects that at least two such faults have become active. The earthquakes are concentrated along two fault zones running north-northwest for about 24 kilometers. Most were detected within 1 kilometer of the surface and were mostly of a magnitude between 2 and 3, consistent with activity in shallow, damaged rock.
The strength of the events has also risen. Earthquake magnitudes were around 1.0 to 1.3 in the early years of the monitoring record. They rose to above 3.0 in 2023 and 2024.
Kim estimated that the 24-kilometer fault zone could produce an earthquake of up to magnitude 6.4 if it were fully reactivated at once. The study does not establish that such an event will occur. It does indicate that geological effects from past tests have persisted well beyond the detonations themselves.
The findings carry implications for monitoring any future nuclear activity at Punggye-ri. Kim and his co-authors warned that earthquakes occurring years after a detonation may make it harder to attribute seismic signals and to distinguish explosion-related events from tectonic ones.
The International Atomic Energy Agency reported that North Korea began restoring test tunnels in March 2022. A 2025 US Defense Intelligence Agency report said North Korea had restored its nuclear test site.
There are no known plans for future tests beneath the peak of Mount Mantap. The Punggye-ri complex surrounding the mountain includes other underground sites where nuclear tests may still be conducted. The researchers said the continuing earthquakes leave open questions about how the seismic trend may develop without further detonations and about the long-term stability of underground facilities in the area.
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