North Korea’s nuclear test faults raise fresh concern over Mount Paektu volcanic eruption

A new study on Friday found that the fault zone around North Korea's Mount Mantap, the site of the country's 2017 nuclear test, has been gradually reactivating for years. Scientists have long worried that testing there could help trigger an eruption at nearby Mount Paektu, an active volcano.

Analyzing 17 years of continuous seismic data in South Korea and northeastern China, a team of South Korean and Chinese researchers found that at Mount Mantap — the site of six underground nuclear tests North Korea conducted between 2006 and 2017 — seismic activity after the largest of the six, in 2017, did not taper off quickly but kept increasing for years.

The findings were published in the journal Science under the title "Nuclear tests at Mt. Mantap have reactivated intraplate faults," with findings by the research team led by Prof. Kim Kwang-hee of Pusan National University's Department of Geological and Environmental Sciences, working with Prof. Fan Xingli's team at Chengdu University of Technology, the Chinese Academy of Sciences, the China Earthquake Administration and researchers at Shandong University.

The team concluded that repeated nuclear tests had accumulated cracks and damage in the rock beneath Mount Mantap and altered the surrounding stress field. As that stress gradually redistributed afterward, it encouraged slippage along the existing faults. Even after the explosions themselves ended, the researchers said, the resulting damage and stress changes can persist underground for years, reactivating dormant faults and generating earthquakes long after the fact.

Typically, underground nuclear tests set off a cluster of small earthquakes or ground collapses immediately afterward, with activity fading within days to weeks, as seen at the United States' Nevada test site and the former Soviet Union's Semipalatinsk site.

The study, however, suggests that seismic activity following an underground nuclear test does not necessarily end quickly and can instead continue evolving for years, depending on geological conditions and the stress state of existing faults. That means earthquakes following a nuclear test should not be read as a short-term event alone, the researchers said, but interpreted alongside a long-term seismic record and physical context.

"What stood out most in this research was that seismic activity continued for years after the 2017 test, and became more clearly concentrated along existing faults over time," said Kim, a co-first author of the study. "We need to keep monitoring seismic activity over the long term even after the explosions have ended, continue building and preserving observational data, and interpret individual earthquakes as part of a long-term physical process."

Lee Jin-han, professor emeritus at Korea University, who studied the 2017 Pohang earthquake linked to human activity, said a future earthquake of magnitude 6.5 or larger, if its rupture propagated northward, could reach the magma chamber beneath Mount Paektu and potentially trigger an eruption. "There should be no more nuclear tests," Lee said, "and the area needs precise monitoring of ground conditions starting now."

A past report from the Ministry of Finance and Economy warned that an eruption at Mount Paektu could rupture Cheonji, the crater lake at its summit, which holds an estimated 2 billion tons of water, and cause major flooding in the surrounding region. The areas expected to be hit hardest are North Korea's Ryanggang and North Hamgyong provinces and China's Jilin province, all of which lie along the Tumen, Yalu and Songhua river basins. Cheonji averages about 12 kilometers (7.46 miles) in diameter and 213 meters (699 feet) in depth.

BY CHOI JOON-HO [[email protected]]