On 5 November 2024, Chinese-born U.S. seismologist Youlin Chen was preparing to fly home to Boston after a monthlong visit to China, where he celebrated his mother’s 80th birthday and gave talks at two universities. For years, Chen, who became a U.S. citizen in 2011, had taken annual trips to China to see family, lecture, and meet with collaborators on projects for his employer, EMR Solutions & Technology, a Florida-based consulting firm.
But that day state security officers arrested Chen at Beijing’s international airport. Officials interrogated him more than 100 times about his research, says Chen’s wife, Yufang Rong, also a seismologist. He was often forced to sit on a hard stool with his hands and legs bound, she adds. Chinese authorities charged Chen with espionage on 1 May 2025 and he remains in detention without a trial, as Reuters first reported earlier this week.
One strand of Chen’s work used Chinese data to analyze North Korea’s six underground nuclear tests for the U.S. Department of State. But none of his work is or was classified, says EMR Senior Vice President Hafidh Ghalib. “He never had a security clearance,” so the company had “no concerns for his safety.”
“This is a really tragic case and one of great concern,” says nuclear nonproliferation expert Siegfried Hecker, a former director of Los Alamos National Laboratory now at Stanford University.
Chen’s detention has heightened alarm over a separate clampdown on the kind of geophysical data he analyzed. Under a policy posted in 2016, seismic networks and other government-funded projects in China were expected to deposit raw observations and processed data in a national data platform operated by the China Earthquake Networks Center. Although CENC restricted access to some sensitive data, other records could be downloaded freely or were available to domestic or foreign users after registration. But on 26 March, CENC’s data platform announced it would no longer provide raw seismic observations or basic information about monitoring stations, except in specially approved cases. Citing data security and national security, it said users would instead receive processed data or customized analyses.
That move, and Chen’s detention, have sent a chill through international seismology. Three U.S. seismologists who have worked with Chinese data declined to be interviewed, citing concerns that their collaborators in China could get in trouble. “This must put tremendous fear into Chinese seismologists who have been collaborating with foreign colleagues,” says Frank von Hippel, a senior research physicist with Princeton University’s Program on Science and Global Security. As one U.S. seismologist put it, “We’re petrified for them.”
Placing China’s raw data off-limits could impede studies of earthquake hazards, fault systems, and Earth’s interior, and make Chinese findings harder for outsiders to reproduce, say the seismologist and others. But Chen’s own research demonstrates how difficult it is to separate civilian and security applications of such work.
Chen had openly collaborated with Chinese government and university seismologists for well over a decade. A collaborative study he led, published in Geophysical Journal International in July 2024, used more than 31,000 waveforms recorded by 346 stations across eastern Asia, including China’s national seismic network, to produce maps of how seismic energy is absorbed by the crust. Such analyses can help estimate the size of seismic sources and improve predictions of ground motion and earthquake hazards. The paper disclosed funding from the U.S. Air Force Research Laboratory and the State Department and thanked CENC staff for providing data and technical support.
The same methods, however, can aid nuclear test monitoring. A December 2020 technical report Chen authored under a contract from the State Department’s arms control bureau sought to improve estimates of the magnitude and yield of North Korea’s nuclear tests and distinguish their signals from natural earthquakes. Ghalib says that, under Chinese rules then in force, Chen analyzed the restricted waveforms in China and did not take the raw records out of the country.
No public evidence links Chen’s detention to CENC’s subsequent data restriction. But the strategic sensitivity of China’s seismic records is illustrated by two small signals detected near China’s Lop Nur nuclear test site in June 2020. In February 2026, U.S. officials alleged that they resulted from a concealed low-yield nuclear explosion; China denies the accusation. International monitoring data were insufficient to determine whether the signals were natural or explosive, and seismologists have said finer grained records from China’s much denser network might resolve the question.
“There are no doubts that seismologists worldwide, including us at EMR, have examined seismic waveforms from events near Lop Nur recorded by stations outside China,” says Ghalib, also a seismologist. Science found no evidence that Chen analyzed the signals using waveforms from Chinese seismometers.
In March 2026, the State Department determined Chen is wrongfully detained. At a media briefing this week, a spokesperson for the Ministry of Foreign Affairs of the People’s Republic of China rejected that designation, stating, “There is no instance of wrongful detention.” A 16 July commentary on the Chinese portal 163.com meanwhile portrayed Chen’s November 2024 visit in a more sinister light. It claimed Chen took “professional seismic detection equipment … into strategic mountainous regions and areas surrounding key civil air defense facilities. There, he surreptitiously deployed temporary monitoring instruments to collect extensive, classified geological data firsthand.”
Rong says such claims are false. “These are crazy stories. He never went to those places and never touched any instruments,” she told Science.
Rong, a seismologist for the insurance firm FM, says she has never collaborated with her husband. But after news broke of his detention, her own collaborators in China sent her frantic messages asking her to remove her name from a paper to appear in the October issue of Engineering Geology. Rong says she tried, but it was too late—the article had already posted online on 26 June.
Chen’s detention has prompted the State Department to consider discouraging U.S. citizens from traveling to China, says Eric Lebson, chief strategy officer at Global Reach, a nonprofit that works to free U.S. citizens held abroad. The department, he says, is also mulling labeling China a State Sponsor of Wrongful Detention. Created by executive order last year, the designation has so far been applied to Iran and Afghanistan. This “could have very serious implications for China,” Lebson says. The designation can lead to sanctions, travel restrictions, export controls, and other penalties.
In the meantime, U.S. and Chinese cooperation in seismology hangs in the balance. “Many of our members, including those in China, depend on data collected and shared by regional and global seismic networks for their research,” the Seismological Society of America, of which Chen is a member, said in a statement.
U.S. embassy staff who have visited Chen and spoken with his lawyer—who was not allowed to see Chen until early this year and is not permitted to discuss the case—have told Rong her husband has lost about 18 kilograms. “We tried to give him shoes for exercise,” she says, “but that was not allowed.”