American expert on underground nuclear tests held in China for over 600 days on espionage charges

A Chinese American seismologist who researched the detection of North Korea's underground nuclear tests using seismic waves has been held in China on espionage charges for more than 600 days.

Global Reach, a US nonprofit that works to secure the release of Americans detained abroad, said Chen Yulin (54) was arrested by Chinese authorities after visiting Beijing in November 2024 to see his family, CNN and the BBC reported Tuesday. His family decided to go public with the case after China showed no signs of releasing him.

Chen was born in China and became a US citizen in 2011. He had been living in Boston, Massachusetts.

Chen's research focused on analyzing seismic waves to determine whether underground nuclear tests had taken place and to estimate the size of any explosion. His work centered primarily on detecting North Korea's underground nuclear tests.

His research received support from the Department of State and the Air Force Research Laboratory. In December 2020, he participated in a joint research project analyzing seismic data from across Asia, including China, to improve techniques for detecting nuclear tests and estimating explosion yields.

Kieran Ramsey, Global Reach's lead investigator, said Chen was arrested at the airport after visiting his parents in Beijing.

"China is under suspicion from the Department of State of violating the Comprehensive Nuclear-Test-Ban Treaty," Ramsey said, "and at the same time is holding an American expert who can pinpoint exactly that."

He added that the case "is an example of China's willingness to use hostage diplomacy in its great-power competition with the United States."

Chen's wife, Rong Yufang, also a seismologist, denied the espionage allegations. She said her husband's research was conducted in collaboration with Chinese scholars using publicly available data, and that "what my husband has been doing aligns precisely with the spirit of civilian and academic exchange that the Chinese government has said it encourages."

Rong said she had not been able to speak directly with her husband for more than 600 days and expressed concern for his health and safety. She said Chinese authorities had interrogated him more than 100 times over the content of his research and denied him access to a lawyer for the first 13 months of his detention.

The James W. Foley Legacy Foundation, a US organization that supports Americans detained abroad, said Chen suffers from diabetes, high blood pressure and high cholesterol. The foundation expressed concern that while he needs consistent medication and medical care, he has been unable to receive reliable treatment at the detention facility.

China's Ministry of Foreign Affairs said at its regular briefing Tuesday that judicial authorities were handling the case in accordance with the law. Spokesperson Lin Jian dismissed US claims, saying "there is no such thing as so-called 'wrongful detention' in China."