Exclusive-China detains US seismologist who has studied North Korean nuclear tests

By Jonathan Landay

WASHINGTON, July 13 (Reuters) – A Chinese-born American seismologist who published U.S.-funded work to detect North Korea’s nuclear tests has been detained in China for nearly two years and is on trial on espionage charges, according to his wife, U.S. lawmakers and two hostage advocacy groups.

The Youlin Chen case, first reported here, further exasperates the tense relationship between the nuclear-armed rivals and comes as President Donald Trump tries to keep the relationship stable after last year’s trade war.

Secretary of State Marco Rubio described Chen, 54, as an “unjust detainee” on March 19 and made his release a top U.S. priority. The Trump administration delayed a public announcement to make room for high-level diplomacy aimed at securing Trump’s freedom, according to his wife, Yufang Rong.

A U.S. source familiar with Chen’s case said the administration was “focused on getting him released from unjust detention.” The source spoke on condition of anonymity to discuss sensitive diplomatic talks.

Chen, who became a U.S. citizen in 2011 and lives in Boston, Massachusetts, is now the only American wrongfully detained in China, according to his wife and hostage advocates.

Rong said the White House and the State Department told her that during his state visit to Beijing in May, Trump promised to discuss her husband’s detention with Chinese leader Xi Jinping and that he would also look into the issue. But Xi said his government had not taken any action.

The US source did not directly confirm that Trump had a meeting between Chen and Xi. But the source said the pair “have a very good personal relationship.” This is one of many aspects of the US-China relationship. “No issue is decisive.”

In a Reuters interview, Rong expressed concern that Beijing had decided to find Chen guilty of espionage even before putting him on trial; this is a possible crime in China, punishable by life imprisonment or even death in cases deemed particularly serious.

“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 has not cooperated with her husband’s work.

Foreign ministry spokesman Lin Jian said at a regular briefing on Tuesday that China’s judicial bodies handle cases in accordance with the law and “there is no such thing as unjust detention.”

The Foley Foundation, a hostage advocacy organization pursuing Chen’s case, believes Chen is among at least 12 Americans wrongfully held in China, said Elizabeth Richards, the group’s director of hostage advocacy.

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

The Office of the Presidential Special Representative for Hostage Affairs did not immediately respond to requests for comment.

HE WAS QUESTIONED ABOUT NUCLEAR TESTING STUDIES

Rong said U.S. embassy officials visited Chen several times, but Chinese officials were always present and prevented him from speaking freely. He hired a Chinese lawyer, but was allowed to see Chen only after more than 13 months in detention.

Rong said Chinese authorities interrogated her husband more than 100 times about his work on seismographic traces of North Korean nuclear tests.

Eric Lebson, a former U.S. national security official whose hostage advocacy organization Global Reach advised the family, said he believed China wanted to use Chen’s expertise to improve its ability to conceal underground nuclear weapons tests through a technique called disintegration.

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

The Trump administration accused China in February of trying to mask the low-yield underground nuclear test explosion on June 22, 2020, by using the technique of detonating a device inside a large underground chamber to reduce the size of the shock waves it produced.

China, which, like the United States, has signed but not ratified the 1996 Comprehensive Nuclear Test Ban Treaty, denies the test was carried out.

Lebson said Chen was employed by a U.S. government contractor and never held a U.S. security clearance or did any classified work.

Lebson said his research on experimental seismic waves in North Korea was funded by the State Department and the Air Force Research Laboratory. He added that this was done in collaboration with Chinese academics, using publicly available Chinese data and viewable on the internet.

Chen’s December 2020 paper, reviewed by Reuters, examined the magnitude of North Korea’s six known nuclear test explosions and ways to distinguish their seismic signatures from earthquake signatures.

The cover page states that the article 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 have broad powers to retroactively classify public data such as official statistics as national security secrets, potentially incriminating anyone who previously possessed or shared open source information.

HE WAS ARRESTED BEFORE RETURNING TO BOSTON

According to Rong and Lebson, Chen was arrested by Chinese state security officials at Beijing International Airport on November 5, 2024, as he prepared to fly to Boston after visiting his family and lecturing about his studies at two universities.

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

He said it was difficult to learn about the conditions of his detention since then, but that he had lost 30 to 40 pounds (13.6 to 18.1 kg), was given inadequate food containing little protein, fruits or vegetables, and received only low-quality medications.

He was charged with espionage on May 1, 2025, but has not yet been tried. The case will likely come up again during Trump’s September visit, when Xi says he will make payments to Washington.

U.S. Sen. Ed Markey, a Massachusetts Democrat who led two other senators in a Dec. 17, 2025, letter urging Rubio to state that Chen was wrongfully detained, said he was “deeply concerned about the safety and well-being of Dr. Chen.”

“Hopefully, the growing attention to his unjust detention will compel the Chinese government to do the right thing and release Dr. Chen,” Markey said in a statement. he said.

(Reporting by Jonathan Landay in Washington; Additional reporting by Michael Martina in Washington and Xiuhao Chen in Beijing; Editing by Don Durfee and Matthew Lewis)