N. Korea's nuclear tests caused over 1,000 earthquakes, study warns

Scientists have detected an unexpected and prolonged increase in seismic activity at North Korea’s sprawling Punggye-ri nuclear test site, with earthquakes continuing to rise for years after the country conducted its final and most powerful nuclear test in 2017.

A study published this week in the journal Science found that the area around Mount Mantap experienced 1,399 earthquakes between 2008 and 2025. The number and magnitude of the earthquakes increased over time, according to seismic wave data collected and analysed by lead author Kwang-Hee Kim in South Korea and his colleagues in China, as an article by Science Alert points out.

Kim, a professor in Pusan National University’s department of geological sciences, said the findings were unexpected.

“We were basically very shocked,” said Kim. “The seismic trend was so clear and linear.”

North Korea carried out six underground nuclear tests between 2006 and 2017 at Mount Mantap in North Hamgyong province. The final test, estimated to have had an explosive yield of 160 kilotons, generated a magnitude 6.3 earthquake and is believed to have caused a collapse at the site, possibly involving a tunnel.

Nuclear explosions have long been known to generate small, detectable earthquakes. Similar activity was recorded after multiple US nuclear tests during the Cold War. However, those effects were generally short-lived, appearing in the days or weeks following an explosion and remaining concentrated around the test site.

At Mount Mantap, the pattern was markedly different. The earliest earthquake identified by the researchers occurred in 2013, following North Korea’s third nuclear test. Seismicity — the relative frequency and intensity of earthquakes — “remained sparse until 2017, when activity increased markedly after the sixth and largest detonation,” the study authors wrote.

Rather than declining after the final test, however, seismic activity at Mount Mantap continued to increase for years.

The researchers believe this could indicate that the Earth’s crust did not return to its previous state following the 2017 explosion. Instead, the test may have helped activate at least two preexisting faults, leading to a sustained increase in the frequency and strength of earthquakes, Kim said.

The Korean Peninsula lies on relatively stable continental crust, unlike Japan to the east. However, the researchers identified ancient “intraplate” faults in the region — fractures in Earth’s crust located far from active tectonic plate boundaries.

The area around Mount Mantap had also been considered seismically quiet before this century. According to the study, earthquakes there were “virtually unknown.”

“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.”

The shape of Mount Mantap could also have contributed to the unusual pattern. The mountain is large, steep and asymmetric, and its irregular topography may have left some faults closer to failure than others. The underground nuclear explosions could then have acted as a trigger.

Global precedence

Delayed and prolonged seismic activity caused by human activity is not unprecedented, according to Sunyoung Park, an assistant professor in the University of Chicago’s department of the geophysical sciences who was not involved in the research.

In the Netherlands, more than 1,700 earthquakes have occurred since gas extraction began in the 1960s, causing damage to property. In Oklahoma, oil and gas production between 2009 and 2015 involved the injection of wastewater underground, a process that was followed by a marked increase in seismic activity.

Park said the nuclear explosions may have fractured a substantial volume of rock, “creating new cracks and pathways for water to move through.”

“As water infiltrates those fractures, it increases pore pressure within the rock,” she said. “That pressure effectively pushes faults apart and makes them easier to slip.” Because water moves slowly through the ground, the resulting seismic activity can be delayed by years, Park added.

The study did not discuss groundwater or determine what role, if any, it may have played in triggering the earthquakes.

“I think the broader lesson is that short-lived disturbances can have consequences that persist for years or even decades,” said Park. “The Earth’s crust has a long memory.”

By Nazrin Sadigova