US Official Unveils New Details on Alleged 2020 Chinese Nuclear Test
A senior United States official has presented what he described as fresh evidence regarding an alleged underground nuclear test conducted by China in June 2020. The claims are based on seismic data recorded at a monitoring station in Central Asia, but Beijing has issued a firm and categorical denial of the allegations.
Seismic Detection and Analysis
Speaking at an event hosted by the Hudson Institute in Washington on Tuesday, Assistant Secretary of State Christopher Yeaw revealed that a remote seismic station in Kazakhstan, designated PS23, detected an explosion with a magnitude of 2.75 on June 22, 2020. According to Yeaw, the signal was traced back to China's Lop Nor test grounds in the western part of the country, approximately 450 miles (720 kilometers) away from the detection site.
"I've looked at additional data since then. There is very little possibility I would say that it is anything but an explosion, a singular explosion," Yeaw stated, as quoted by Reuters. He emphasized that the seismic patterns were inconsistent with typical mining blasts or natural earthquakes. "It's also entirely not consistent with an earthquake. It is ... what you would expect with a nuclear explosive test," he added.
International Monitoring and Response
The PS23 station is part of the global monitoring network operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which is specifically tasked with detecting nuclear test explosions worldwide. However, the agency has indicated that it lacks sufficient data to confirm the US allegations with a high degree of confidence.
CTBTO Executive Secretary Robert Floyd clarified that the station recorded two very small seismic events occurring 12 seconds apart on June 22, 2020. He noted that while the organization's system can detect events consistent with nuclear test explosions yielding 551 tons (500 metric tons) of TNT or greater, these two events were far below that threshold. "As a result, with this data alone, it is not possible to assess the cause of these events with confidence," Floyd explained.
China's Strong Rejection and Accusations
China has vehemently rejected the allegations. Liu Pengyu, a spokesperson for the Chinese embassy in Washington, dismissed the claim as "entirely unfounded" and characterized it as an attempt "to fabricate excuses for resuming" US nuclear testing.
In an emailed statement cited by Reuters, Liu asserted, "This is political manipulation aimed at pursuing nuclear hegemony and evading its own nuclear disarmament responsibilities." He further urged the United States to reaffirm the commitment of the five nuclear-weapon states to refrain from nuclear tests, uphold the global consensus against such tests, and take concrete steps to safeguard the international nuclear disarmament and non-proliferation regime.
The Concept of Decoupling
Assistant Secretary Yeaw suggested that China might have employed a technique known as "decoupling" to conceal the alleged test. Decoupling involves detonating a nuclear device inside a large underground chamber, which can significantly reduce the shockwaves recorded by seismic sensors.
According to the National Academies of Sciences, Engineering, and Medicine, in a fully decoupled underground blast, most of the explosive energy is absorbed by sharply increasing gas pressure inside the cavity—potentially reaching up to 100 times atmospheric pressure—rather than being transmitted into the surrounding rock. This contrasts with a normal "well-coupled" underground explosion, where much of the energy melts and deforms nearby rock, generating stronger seismic waves that are easier to detect.
Broader Context and Nuclear Arsenals
China has signed but not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty and denies conducting any underground nuclear tests since that year. Similarly, the United States has signed but not ratified the pact and last conducted an underground nuclear test in 1992.
These allegations emerge against a backdrop of growing concerns over nuclear arms control, particularly following the expiration of the New START treaty on February 5. US President Donald Trump has called on China to join Washington and Moscow in negotiating a replacement agreement, a proposal that Beijing has rejected, citing its significantly smaller nuclear arsenal compared to those of the United States and Russia.
The Pentagon estimates that China currently possesses more than 600 operational warheads and is actively expanding its strategic nuclear forces. Projections indicate that the country could field over 1,000 warheads by the year 2030, highlighting the escalating dynamics in global nuclear capabilities and the urgent need for diplomatic engagement and transparency.
