A Chinese-born American seismologist who specializes in detecting nuclear tests has been detained in China for nearly two years on espionage charges, with his family and supporters insisting his research was open, collaborative and focused on North Korea’s weapons programme.
A Chinese-born American scientist known for his research on North Korea’s nuclear tests has been detained in China on espionage allegations, prompting growing concern from his family, US officials and advocacy groups.
Chen Youlin, a 54-year-old seismologist and naturalised US citizen, was arrested in Beijing in November 2024 while visiting relatives, according to the US-based hostage advocacy organisation Global Reach.
His detention remained largely out of the public eye until this week, when his family decided to speak publicly after months of unsuccessful efforts to secure his release.
Chen’s wife, Rong Yufang, who is also a seismologist, strongly rejected the accusations, describing her husband’s work as transparent and grounded in international scientific collaboration.
“The allegations are both wrong and inconsistent with the public and collaborative nature of the work that he has done,” she said in a statement.
Chen’s research has focused primarily on using seismic data to detect underground nuclear explosions, particularly those carried out by North Korea, whose nuclear weapons programme has long been monitored by scientists around the world.
Although it remains unclear whether his research intersected with China’s own nuclear activities, US intelligence agencies have previously alleged that Beijing is expanding its nuclear arsenal and has conducted undisclosed nuclear-related tests. China has consistently denied those claims.
Responding to questions about Chen’s detention, China’s Foreign Ministry defended the country’s legal process.
Foreign ministry spokesman Lin Jian told reporters that Chinese judicial authorities handle cases in accordance with the law and dismissed suggestions that the scientist had been wrongfully detained.
“There is no such thing as so-called wrongful detention,” he said.
Under Chinese law, espionage convictions can carry severe penalties, including life imprisonment or the death sentence.
According to Chen’s wife, the scientist has been questioned more than 100 times since his arrest and was denied access to legal representation during the first 13 months of his detention.
She also revealed that she has been unable to speak with her husband for more than 600 days and fears his health may be deteriorating.
Chen, who became a US citizen in 2011 and lives in Boston, Massachusetts, has worked on several research projects funded by the US government.
His expertise lies in analysing seismic waves generated by underground explosions to distinguish nuclear tests from natural earthquakes.
One of his published studies, released in late 2020, examined seismic data collected across Asia, including stations located in China, to improve methods of identifying underground nuclear explosions and estimating their explosive yield.
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Rong insisted that every aspect of her husband’s work with Chinese researchers was conducted openly and in line with accepted scientific practices.
“He is doing precisely the kind of people-to-people engagement that the Chinese government says it wants,” she said.
Global Reach believes Chen’s arrest may be linked to broader concerns surrounding China’s nuclear programme.
The organisation said some US officials suspect Chinese authorities detained Chen after becoming concerned about his expertise in detecting covert nuclear tests.
According to the advocacy group, his knowledge of American seismic monitoring methods could help China better understand how nuclear tests are detected and potentially develop ways to avoid future detection.
The case has also renewed attention on the Comprehensive Nuclear-Test-Ban Treaty, which seeks to prohibit all nuclear explosions worldwide.
Although both the United States and China have signed the treaty, neither country has formally ratified it. Both governments currently observe voluntary moratoriums on explosive nuclear testing.
During Donald Trump’s first administration in 2020, Washington accused China of secretly conducting underground nuclear tests at the Lop Nur testing site in Xinjiang. Beijing rejected the accusation, describing it as politically motivated and without evidence.
Health concerns have also emerged as Chen remains in detention.
The Foley Foundation, another US-based organisation that advocates for Americans detained abroad, said the scientist suffers from diabetes, high blood pressure and high cholesterol.
The group warned that he requires consistent medical treatment that may not be available while he remains incarcerated.
US Senator Edward Markey called for Chen’s immediate release, arguing that the detention damages scientific cooperation between the United States and China and could discourage future academic exchanges.
“It is my hope that increased attention on his unjust detention will force the Chinese government to do the right thing and release Chen,” the Massachusetts senator said.
Chen is currently the only American citizen officially designated by the US government as being wrongfully detained in China.
His case comes just weeks after Beijing confirmed the arrest of another US-linked scholar, Myanmar expert Min Zin, who has also been accused of espionage and endangering China’s national security.
As diplomatic tensions between Washington and Beijing continue, Chen’s detention is likely to become another sensitive issue in an already strained relationship between the world’s two largest economies.
