North Korea's Nuclear Tests Turned Mount Mantap Into Quake Zone

A new Science study finds 1,399 earthquakes have intensified around North Korea's Punggye-ri test site years after the last 2017 blast.

Researchers led by seismologist Kwang-Hee Kim of Pusan National University report that North Korea's six underground nuclear tests at Mount Mantap between 2006 and 2017 reactivated previously quiet faults. Using matched-filter detection on 17 years of seismic recordings from stations in China and South Korea, the team identified 1,399 earthquakes spanning 2008 to 2025. The quakes mapped onto two roughly parallel fault-like structures running north-northwest from the test site, one continuing a fault already mapped south of Punggye-ri.

Typical post-explosion seismicity begins promptly and fades as the transient disturbance dissipates. Instead, activity at Mount Mantap began about 20 days after the final test and intensified for years. "Both the earthquake rate and seismic moment release continued to increase through May 2025, the end of our study period," Kim told ScienceAlert. CNN reports Kim was "basically very shocked" that "the seismic trend was so clear and linear." The area was historically near-silent, with just one crustal event within 200 kilometers between 23 BCE and 1903 CE.

The final test on 3 September 2017 was the largest, with an estimated yield of 100 to 250 kilotons per ScienceAlert — Scientific American says the equivalent of up to 20 Hiroshima bombs — producing a magnitude 6.3 signal. A magnitude 4.1 cavity collapse followed 8.5 minutes later. The team traced 955 quakes precisely, mostly magnitude 2 to 3 and shallow, and concluded the tests disturbed crust already close to failure. "The Earth's crust has a long memory," University of Chicago's Sunyoung Park told CNN.

Scientific American notes Mount Mantap is now an archetypal "tired mountain," fractured so badly it can no longer contain radioactive gases, and that the 2017 blast effectively collapsed the peak's top. The longer fault-like structure stretches about 24 kilometers; if it ruptured along its full length, researchers estimate it could theoretically produce a magnitude 6.4 earthquake — a hypothetical, not a prediction. The persistent seismicity may also complicate nuclear-test monitoring by blurring distinctions between explosion-related and tectonic events.

The authors argue geological consequences of underground nuclear testing may need monitoring far longer than previously appreciated, both at Punggye-ri and other sites near stressed faults. CNN reports the IAEA said North Korea began restoring test tunnels in March 2022, and a 2025 US Defense Intelligence Agency report stated the test site had been restored, though Kim said the team had no evidence of further tests since 2017. Park suggested infiltrating water may be raising pore pressure on faults, a possible delayed mechanism the study did not examine.