China detains US seismologist who has studied North Korean nuclear tests

WASHINGTON – A Chinese-born American seismologist who has published US-funded work on detecting North Korean nuclear tests has been detained in China for nearly two years and faces trial on spying charges, according to his wife, US lawmakers and two hostage advocacy groups.

The case of Youlin Chen, reported here for the first time, adds an irritant to the tense relationship between the nuclear-armed rivals and comes as President Donald Trump seeks to keep the relationship steady following the trade war in 2025.

Secretary of State Marco Rubio on March 19 designated Chen, 54, as “wrongfully detained,” making his release a top US priority.

The Trump administration has withheld a public announcement to allow space for high-level diplomacy aimed at securing his freedom, according to his wife, Yufang Rong.

A US source familiar with Chen’s case said the administration was “focused on gaining his release from his unjustifiable detention.”

The source spoke on condition of anonymity to discuss sensitive diplomatic talks.

Chen, who became a US citizen in 2011 and lives in Boston, Massachusetts, is the only American currently held in China designated as wrongfully detained, according to his wife and hostage advocates.

Rong said she has been told by the White House and the State Department that during a state visit to Beijing in May, Trump raised her husband’s detention with Chinese leader Xi Jinping, who promised to look in to it. Xi’s government, however, has taken no action, she said.

The US source did not directly confirm that Trump discussed Chen with Xi. But the source said the pair have a “very good personal relationship. This is one of many facets in the US-China relationship. No one issue is defining.”

In a Reuters interview, Rong expressed concern that Beijing has decided even before putting Chen on trial to find him guilty of espionage, a crime that in China carries a possible sentence of up to life in prison or even the death penalty for cases deemed especially grave.

“I believe they will convict him no matter what and the trial will be behind closed doors,” said Rong, who is also a seismologist but does not collaborate on her husband’s work.

The Foley Foundation, a hostage advocacy organisation that has been tracking Chen’s case, believes that Chen is among at least 12 Americans unjustly held in China, including people under exit bans, said Elizabeth Richards, the group’s director of hostage advocacy.

“President Trump has been clear that he wants every American detained abroad to return home, and he has reunited over 100 individuals with their families since taking office this term,” said deputy White House press secretary Anna Kelly.

The Office of the US Special Presidential Envoy for Hostage Affairs and the Chinese embassy did not immediately respond to requests for comment.

Interrogated about nuclear test studies

US embassy officials have visited Chen several times, but Chinese officials are always present, preventing him from speaking freely, said Rong. She retained a Chinese lawyer, but he was allowed to see Chen only after he had been detained for more than 13 months.

Chinese officials have interrogated her husband more than 100 times about his work on the seismographic signatures of North Korean nuclear tests, said Rong.

Eric Lebson, a former US national security official whose hostage advocacy organisation, Global Reach, is advising the family, said he believes China wants to use Chen’s expertise to improve its ability to conceal underground nuclear weapons tests through a technique called decoupling.

Lebson said a similar concern was expressed by experts on nuclear testing consulted by his group.

The Trump administration in February accused China of trying to mask a low-yield underground nuclear test blast on June 22, 2020, using the technique in which a device is detonated inside a large underground chamber to reduce the magnitude of the shock waves it produces.

China, which like the US has signed but not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty, denies conducting the test.

Lebson said that Chen is employed by a US government contractor, and has never had a US security clearance or performed classified work.

His research on North Korean test blast seismic waves has been funded by the State Department and the Air Force Research Laboratory, said Lebson. He added that it was done in collaboration with Chinese academics, it used publicly available Chinese data and is viewable on the internet.

A December 2020 paper by Chen reviewed by Reuters examined the magnitude of North Korea’s six known nuclear test blasts and ways to differentiate their seismic signatures from those of earthquakes.

The cover page states that the paper was written for the State Department’s arms control bureau and “approved for public release.”

Human-rights groups have argued that under China’s state-secrets law, Chinese authorities retain broad powers to retroactively classify public data, such as official statistics, as national security secrets, potentially implicating anyone who possessed or shared previously open-source information.

Arrested before returning to Boston

Chen was arrested by Chinese state security officers on Nov 5, 2024, at Beijing International Airport as he prepared to fly home to Boston after visiting family and lecturing on his work at two universities, according to Rong and Lebson.

At the beginning of his detention, said Rong, Chen was subjected to “harsh conditions,” including being forced to sit all day on a hard stool without being allowed to stand, read or exercise, and was unable to obtain medications for his diabetes and other health problems.

Since then, she said, it has been difficult to learn the conditions of his confinement, but she added that he has lost 13kg to 18kg, is given insufficient food with little protein, fruits or vegetables, and receives only poor-quality medications.

He was charged with espionage on May 1, 2025, but has not yet stood trial. The case likely will come up again during a visit that Trump has said Xi will pay to Washington in September.

US Senator Ed Markey, a Massachusetts Democrat who led two other senators in a Dec 17, 2025, letter urging Rubio to designate Chen as wrongfully detained, said he was “deeply concerned about Dr Chen’s safety and wellbeing.”

“It is my hope that increased attention on his unjust detention will force the Chinese government to do the right thing and release Dr Chen,” Markey said in a statement. REUTERS