Fact Sheet: Tremendous progress in the build-up of the CTBT's verification regime

Over the last decade, considerable progress has been made in the build-up of the unique verification regime to monitor the globe for nuclear explosions. The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is working hard to complete the International Monitoring System, which is now more than 70 percent operational and that will consist of over 300 stations when ready. As an additional verification layer, the procedures for on-site inspections have been established and tested in the field. As a result of progress over recent years in monitoring technologies and the computerized evaluation of measuring data, the system is already able to detect any militarily relevant nuclear test - anywhere on the planet. To illustrate this, we'd like to go back to the North Korean nuclear test in 2006 and show you what we were able to detect at that time...But first, we'd like to give you a short overview.


The Comprehensive Nuclear Test-Ban Treaty's (CTBT) verification regime consists of three main elements. Firstly, there is the International Monitoring System with 337 monitoring facilities around the globe. Seismic, infrasound and hydroacoustic stations pick up sound and energy waves generated by explosions. Radionuclide and noble gas stations trace radioactive particles and gasses, which indicate whether or not a given explosion is nuclear.

Click here for animation of how data is transmitted from the International Monitoring System.

The monitoring stations send real-time data to the International Data Centre in Vienna, the second arm of the verification regime. Data from the stations are forwarded instantly to all CTBTO Member States, and are also analyzed by our experts and provided as data bulletins to the Member States.

The final arm of our verification regime is an on-site-inspection: the in-the-field, eyes-on-the-ground component, which can only be invoked after entry into force of the CTBT.

Watch a clip on the International Data Centre in Vienna, Austria.

Baptism of fire – the North Korean nuclear test

On 9 October 2006, North Korea announced that it had conducted a nuclear test - the first real-life test for our system. As it was an underground explosion, we looked at data from the seismic stations first. The CTBT specifies that data from three stations are needed in order to include an event into our data bulletins. In this case, 22 of our stations registered the shock waves of the explosion.

22 stations picked up the North Korean nuclear test, some thousands of kilometres away.

Within minutes, we were able to provide the first set of data about the location, time and magnitude of the event to our Member States. Stations as far away as La Paz, Bolivia, picked up the explosion. The shock waves travelled for 22 minutes to reach this station. It turned out that the explosion was low in yield: 0.5 kilotons. Nevertheless, the seismic readings were precise enough for us to determine the location and area for an on-site inspection, which cannot be larger than 1000 km² according to the Treaty.

CTBTO experts compared seismograms for the declared nuclear test to an earlier earthquake on the North Korean peninsula.

Detecting the "Smoking Gun"

After the North Korean test, Member States and journalists bombarded us with questions such as: “What did you find out?” or “Was it a nuclear explosion?” However, for us to prove the nuclear character of the explosion and to find the "smoking gun", it was necessary to detect not only seismic signals, but also radioactive particles. First of all we calculated how long it would take the radioactive noble gases from an underground explosion of that yield at that location to reach the surface. Then our experts applied the so-called method of atmospheric transport modelling (ATM) to calculate where the winds would carry these particles and if and when they would reach one of the noble gas stations. We hoped for early readings from the stations in Japan and Mongolia but the winds did not blow in those directions. In the end, a station in Canada – 7500 km away – picked up minute traces (as little as 300 atoms) of the noble gas Xenon 133 two weeks after the test and exactly as we had calculated. We were able to exclude any other known source for the findings at the Canadian station. It was the North Korean explosion. Read more on the CTBTO's findings with regard to the North Korean test here.

Click for animation: A method called atmospheric transport modelling is used to calculate the potential trajectory of an airborne radioactive particle.

Tremendous progress over the past decade

What was the significance of the North Korean test for CTBT verification? In October 2006, only 180 or slightly more than 50% of our stations were ready. Only 10 noble gas systems?or 25 percent ?were in place. Nevertheless, our system performed well - better than had been originally expected by Treaty negotiators in 1996 for the completed system: - The seismic component could clearly register an explosion of less than 1 kiloton. - The enormous verification value of the noble gas technology was proven.

- The necessity and importance of on-site-inspections, as the final tool to verify a nuclear test explosion, was underlined.

The noble gas systems were more than doubled since 2006, from 10 to 22.

Working hard to complete the system

Today, we have more than doubled the number of our noble gas systems from 10 to 22. When complete, the noble gas network will consist of 40 systems. Regarding the entire International Monitoring System, we have increased the number of stations from 180 to 250 since 2006. This means that today, 75 percent of our network is in place; see interactive map. The additional stations have significantly enhanced the verification capabilities of the system.

Since October 2006, the number of stations increased from 180 to 250.

In October 2006, the capability of the system was already clearly better than 1 kiloton in many parts of the world (see right). Today, the additional seismic stations that have been built since then have further improved detection capability. And this only relates to the primary seismic system; the larger auxiliary seismic network is not included. Neither are the noble gas systems nor on-site inspections, which would work in synergy with the seismic systems.
Advances in sciences and technologies Overall, the past decade has seen considerable advances in the sciences and technologies relevant to CTBT verification: - Detection and location of nuclear tests and data analysis have improved through better computers and software. A particular case in point is the noble gas technology. This was very much at an early experimental stage in the 1990s. The potential of this new technology has only really become usable for CTBT verification in the past few years. Our ability to detect and identify nuclear explosions has significantly increased with this new and powerful verification tool. - The seismic network also has a better detection capability compared to the 1990s. In addition, there is a dense network of non-CTBT seismic systems available for States. The better understanding today of Earth-models has enhanced the ability to comprehend and interpret seismic observations. - Considerable progress has been made in developing our on-site-inspection capabilities.

Average Detection Capability of the primary seismic component in 2006 (top) and today. Magnitude 4 (light green to dark green) represents roughly an explosion yield of 1 kiloton.

A high degree of confidence

We can now say, with a high degree of confidence, that compliance with this Treaty can indeed be monitored. With the additional national technical means of verification and the possibility of an on-site inspection, a violation of the Treaty’s principles cannot go unnoticed. That any nuclear test of military significance, regardless of its location, cannot go undetected. To conclude, the issue of CTBT verifiability is different today than it was ten years ago. Click here (PDF) for viewing the above and additional images on progress in the verification regime in higher resolution.

CTBTO Executive Secretary Tibor Tóth: "No nuclear test of military significance can go unnoticed".