Next phase in the analysis
of the announced DPRK nuclear test

At a meeting of Signatory States of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) yesterday, 26 May  (see press release), the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) informed delegates on the progress in the analysis of its findings on the nuclear test declared by the Democratic People’s Republic of Korea (DPRK) on Monday, 25 May. The CTBTO issued its first information to the Signatory States at 02.24 A.M. (GMT) - before the DPRK had officially announced the test - containing the location, magnitude, depth and time of the event. This information was further updated within two and four hours. On Monday morning, a technical briefing to Signatory States provided additional information.

Complex seismic signals

CTBTO experts explained that they continued to study the signals detected by the seismic stations of the International Monitoring System (IMS). The seismic data seemed to be more complex than from typical explosions. The signals have been recorded by a larger number of IMS seismic stations. CTBTO experts concluded that the recorded signals contain distinct characteristics of an explosion. In addition, they also identified simultaneous signals with earthquake–like characteristics.

Tracking down radioactive particles

Underground explosions typically release radioactive noble gases, which can be detected – depending on the amount released – by certain IMS stations. Noble gas is the “smoking gun” of a nuclear explosion. The detection of airborne radioactive substances depends on the prevailing meteorological situation. By applying a technique called Atmospheric Transport Modelling (ATM), the three-dimensional travel path of a radionuclide particle or noble gas is backtracked from where it was detected by a monitoring station, to the area where it may have originated – and vice-versa. After the 2006 nuclear test, traces of the radioactive noble gas xenon133 – an isotope that does not exist in nature - were detected by a station in Yellowknife, Canada; some 7500 km away from the test site and 12 days after the event. As the network of noble gas-capable stations has grown denser today – up from 11 to 22 systems (40 anticipated at the entry into force of the CTBT), with the higher density of stations now running in the region, it may be possible to detect radioactive noble gas within days rather than weeks, assuming that radioactive noble gases have been released into the atmosphere. The system’s capabilities were also boosted through the establishment of a joint response system with the World Meteorological Organization (WMO) last September, which allows the CTBTO to utilise additional atmospheric transport models in order to make more precise ATM calculations.
The CTBTO will provide an update if and when noble gas has been detected and analyzed.


A verification regime is being built to monitor compliance with the CTBT. 337 facilities worldwide will monitor the underground, the oceans and the atmosphere for any sign of a nuclear explosion. Today, 246 facilities have been certified and incorporated into the network, and can send data to the International Data Centre at the CTBTO in Vienna.

The CTBT has been signed by 180 States and ratified by 148, see interactive map. For its entry into force, however, the following nine States have yet to ratify: China, DPRK, Egypt, India, Indonesia, Iran, Israel, Pakistan, and the United States.

For further information, please see our special DPRK 2009 page at – your resource on stopping nuclear testing, or contact:  Annika Thunborg, Chief, Public Information  
T    +43 1 26030-6375  
E    [email protected]
M    +43 699 1459 6375 Download picture or video files on the CTBTO.