Preliminary Seismic Assessment of the 22 June 2020 Event near Lop Nor

Background

U.S. Under Secretary for Arms Control and International Security Thomas G. DiNanno claimed in a presentation in Geneva on 6 February 2026 that China conducted a low-yield nuclear test explosion on 22 June 2020, in violation of the Comprehensive Nuclear-Test-Ban Treaty. In a speech at the Hudson Institute on 17 February 2026, Christopher Yeaw, Assistant Secretary of the Bureau of Arms Control and Nonproliferation, provided a specific time — 09:18 UTC — for such an explosion near Lop Nor in China.

NORSAR PRESS RELEASE:

In response, NORSAR undertook a review of available seismic data from the region. As part of this work, NORSAR conducted a systematic scan of the full 24-hour period of 22 June 2020. This analysis was carried out in the days following the 6 February public statement and prior to the subsequent U.S. announcement on 17 February 2026 identifying a specific time of interest. Through this independent screening process, NORSAR identified a small seismic event occurring at approximately 09:18 UTC as the only signal on that day potentially compatible with a source in the Lop Nor region. The later U.S. statement referring to the 09:18 UTC event is consistent with the timing identified through NORSAR’s independent analysis.

The 09:18 UTC event is clearly recorded at a high-sensitivity seismic array in Kazakhstan, located approximately 740 km from the Lop Nor test area. The direction and timing of the signal are compatible with a source in that region. However, the signal is clearly observed at only one primary array. Other regional stations did not record strong supporting signals, and a nearer Chinese station shows only weak observations. As a result, the precise epicentral location cannot be tightly constrained.

The event has an estimated local magnitude in the range of approximately 2.5–3.0. U.S. officials have referred to a magnitude of 2.75, which lies within this range. Small differences in reported magnitude are expected due to methodological and observational uncertainties, and it is scientifically appropriate to express the estimate as a range.

If interpreted as a normally coupled underground explosion — meaning no measures were taken to reduce seismic signals — a magnitude in this range would correspond approximately to an explosive yield in the range 3 to 15 tonnes of TNT equivalent. If significant seismic decoupling were employed, the true yield could in principle be substantially larger, potentially in the several hundred tonne range and, under idealised conditions, above one kiloton. These yield figures represent illustrative scenarios based on modelling assumptions rather than direct measurements.

The signal shows relatively strong compressional (P) waves compared to shear (S) waves, a feature that can be consistent with explosive sources. However, this characteristic alone is not diagnostic. Natural earthquakes can produce similar patterns, particularly when observations are limited to a single high-quality station.

Further analysis is ongoing, including detailed waveform comparison and correlation studies to assess how unusual the 09:18 UTC signal is relative to background seismicity in the region.

Based on the currently available seismic data, NORSAR cannot confirm or refute the allegation that a nuclear test took place on 22 June 2020. The observed signal is compatible with a small event in the Lop Nor region and exhibits characteristics that can be associated with explosive sources. However, those characteristics are not unique to explosions, and the data do not rule out that the event could have been a small natural earthquake. Limited station coverage prevents definitive source identification at this stage.

Birger Sten, CEO NORSAR

Mail: b@norsar.no

Phone: + 47 9008 8222

Ben Dando

Head of Seismology and Verification: National Data Centre

Mail: benjamin.dando@norsar.no

Phone: +47 4681 3190