Between 2006 and 2017, North Korea conducted six underground nuclear tests in tunnels dug under Mount Mantap, located in the northeast of the country. This place, far from civilization, was chosen not by accident - the massive layer of rock was supposed to effectively dampen the effects of the explosion and limit the spread of radiation.
The last test, conducted on September 3, 2017, was the most powerful - its power is estimated at 100 to 250 kilotons, which is even a dozen times more powerful than the bomb dropped on Hiroshima. The explosion caused a shock equivalent to an earthquake with a magnitude of 6.3. Just a few minutes after the detonation, an aftershock with a magnitude of 4.1 was recorded, which scientists interpret as the collapse of the underground chamber resulting from the explosion.
A surprising sequence of earthquakes
Although the immediate effects of the explosions were expected, the real surprise came from the events that followed. Instead of a gradual cessation of seismic activity, as usually happens after such explosions, the region beneath Mount Mantap began to experience more and more frequent and stronger earthquakes - over the following years.
Geologists from South Korea and China analyzed seismic data from 2008 to 2025, using advanced techniques to detect even the smallest quakes that previously went unnoticed. The results were shocking - as many as 1,399 earthquakes were identified, most of which occurred after the last test in 2017.
A region that had previously been almost completely peaceful
Analysis of historical seismic data has shown that the Mount Mantap area has been almost free from major earthquakes for hundreds of years. No significant tremors were recorded within a 50-kilometer radius of the test site from the early 20th century until 2017. Only after the third nuclear test in 2013 did the first, very weak signals of seismic activity appear.
The situation changed dramatically after the sixth, largest explosion. Just three weeks after the detonation, the region began to tremble regularly, and the number and strength of tremors not only did not decrease, but actually increased every year.
Dormant fault lines come to life
Detailed analysis of the earthquake locations revealed that they were not randomly scattered. Most of them were arranged in two parallel bands, which correspond to the course of known and previously unknown tectonic faults. This suggests that nuclear explosions disturbed the delicate balance in the Earth's crust, activating previously dormant geological structures.
Scientists compare this process to a stack of blocks that has already been on the verge of toppling over. A series of strong shocks - in this case caused by explosions - could have shifted the distribution of forces in such a way that, even after the tests were completed, further fragments of the crust began to move, triggering earthquakes.
Threat of a large earthquake
One of the discovered fault strands stretches for approximately 24 kilometers. If it moved simultaneously, it could cause an earthquake with a magnitude of up to 6.4 on the Richter scale. For now, however, there is no evidence that such a scenario is inevitable - this structure may well consist of many smaller segments that will move gradually.
Nevertheless, research shows that the effects of underground nuclear testing may be much more long-lasting and unpredictable than previously thought. It is also a serious challenge for scientists monitoring seismic activity - the distinction between natural earthquakes and those caused by human activity is becoming increasingly difficult.
Long-term consequences for safety and science
Geologists' discoveries shed new light on the risks associated with underground nuclear weapons tests. It turns out that even many years after the last explosion, regions such as Mount Mantap may remain seismically active, and the number and strength of earthquakes may increase. This is not only a challenge for local communities and infrastructure, but also for international systems for monitoring nuclear tests.
