N. Korea nuclear tests reactivated dormant faults: study

Repeated nuclear tests at North Korea’s Punggye-ri site appear to have reactivated dormant faults beneath Mount Mantap, triggering more than 1,000 earthquakes in the area, a new study has found.

A research team led by Kim Kwang-hee, a professor of geological sciences at Pusan National University, analyzed seismic data collected in South Korea and northeastern China over 17 years, from 2008 to May 2025. The study, conducted jointly with researchers from several Chinese institutions, was published Friday in the international journal Science.

The research found that repeated underground nuclear explosions progressively damaged the shallow crust and altered stress on nearby faults, causing previously quiet fault zones to become active.

Historical earthquake records showed no seismic activity around Mount Mantap before North Korea began nuclear testing at the Punggye-ri site in 2006. About 60 earthquakes were detected between 2006 and the sixth nuclear test in 2017, with seismic activity gradually increasing after the third test in 2013.

The most dramatic change came after the sixth and most powerful test in 2017. Seismic activity intensified about 20 days later and some 1,330 earthquakes have since been detected, concentrated along two north-northwest-trending fault zones stretching about 24 kilometers.

The earthquakes also became stronger over time, rising from magnitudes of around 1.0 to 1.3 in the early years to above 3.0 in 2023 and 2024. The strongest recorded earthquake reached magnitude 3.4.

Kim estimated that the 24-kilometer fault zone could generate an earthquake of up to magnitude 6.4 if it were fully reactivated at once.

The research team said repeated explosions likely caused cracks and damage to accumulate in the shallow crust beneath Mount Mantap, while changing stress conditions in surrounding areas and gradually reactivating dormant faults.

The earthquakes were also unusually shallow. While earthquakes in Korea typically occur at depths of around 15 kilometers, most of those around Mount Mantap were detected within 1 kilometer of the surface.

The findings suggest the geological effects of underground nuclear tests can persist and even intensify for years after testing ends, depending on local geological conditions and the stress state of nearby faults.

The researchers said the results could also have implications for monitoring former nuclear test sites, as delayed earthquakes caused by testing may be difficult to distinguish from naturally occurring seismic activity.