New Delhi: Nuclear tests at North Korea’s Punggye-ri site beneath Mount Mantap reactivated dormant plate fault lines, causing earthquakes years after the tests were over. According to a new study published in Science, scientists from Pusan National University discovered that six underground nuclear tests between 2006 and 2017 caused 1,399 local earthquakes from 2008 to 2025.
The study said that this phenomenon observed at Mt Mantap was unlike historical nuclear explosions, such as those in Nevada and Semipalatinsk in Kazakhstan.
“Underground nuclear explosions typically produce short-lived seismic sequences that decay rapidly after testing ceases. (North Korea tests) challenge conventional expectations, showing that under specific geological conditions, underground nuclear testing can drive multiyear fault reactivation,” the report read.
Most underground nuclear test sites are situated in shafts or tunnels, and explosions during the testing phase can cause seismic waves. According to the study’s measurements, the final test at the site, on 3 September 2017, was North Korea’s largest and had an estimated explosion yield of 160 kilotonnes.
This resulted in a magnitude 6.3 earthquake, which pushed the mountaintop up by 3.5 metres, and even led to a cavity collapse inside the tunnels.
The study examined seismic waveform data from regional stations in China and South Korea, which are around 80 to 200 kms away, over 17 years to understand the long-term impact of these explosions and detonations, if any.
Scientists also noted that earlier, between 1904 and 2017, this continental crust near Mt Mantap, which is located in the North Hamgyong province, was almost inert. There were no records of crustal earthquakes within 50 kms of the site for more than a century before the tests occurred. Yet after the tests, sustained tectonic fault movement was observed from 2017 to 2025, and it steadily increased.
However, the Pusan scientists did have an explanation for why this long-term tectonic movement was observed in the region, as it has to do with the specific geographical location of the site near existing fault lines, the steep topography of the mountain itself, and the pressure of successive explosions.
Out of the 1,399 earthquakes, only 955 had epicentres, which showed that the earthquakes were occurring across two clearly defined fault lines in the crust. Unlike plate tectonic boundaries, fault lines are cracks in the Earth’s surface left by ancient tectonic movement, and they often dictate seismic activity.
“Our observations indicate that repeated underground explosions modified the local stress field and progressively damaged the shallow crust,” the study read.
But extensive explosions have occurred in other underground nuclear test sites across the world as well, and yet have only triggered seismic activity for a few days. The reason why Mt Mantap saw such an extended impact is that it has very steep, asymmetrical slopes, which contributed to additional pressure on the Earth’s crust.
While the study put forward these theories to explain the unusual earthquake activity after North Korea’s nuclear tests, it also said this incident called for greater monitoring of nuclear activity under the Comprehensive Nuclear Test Ban Treaty (1996).
“Seismicity occurring years after detonation may complicate attribution and blur distinctions between explosion-related and tectonic events. Sustained monitoring and physically informed interpretation are therefore essential,” said the study.
(Edited by Insha Jalil Waziri)