US expert on underground nuclear tests detained in China for 18 months, family reveals

A Chinese-born American seismologist, Youlin Chen, who conducted U.S.-funded research on detecting underground nuclear tests, has been detained in China since November 5, 2024, on espionage charges. His family recently revealed his prolonged detention, nearly two years after his arrest, citing deep concerns for his health and well-being due to harsh conditions. Chen, a 54-year-old U.S. citizen, was formally charged with espionage in May 2025, but a trial has not yet taken place.

The U.S. government officially designated Chen as "wrongfully detained" in March, making his release a top priority. U.S. President Donald Trump reportedly appealed directly to Chinese President Xi Jinping during a state visit to China in May for Chen's freedom, with Xi purportedly agreeing to address the matter. However, Chen's family and advocacy groups state that no visible progress has been made toward his release.

Advocates suggest China might be interested in Chen's expertise in seismic detection to develop methods for concealing its own underground nuclear tests, a claim denied by Beijing, which maintains that the case is being handled lawfully. This detention further strains already tense relations between the two countries, with Chen being the only American currently designated as wrongfully detained in China.