CTBT ratification still uncertain after 15 years of advancement in nuclear test monitoring

Credit: The International Monitoring System. Image credit: The Comprehensive Nuclear-Test-Ban Treaty Organization.

There is still no timetable for when the Comprehensive Nuclear-Test-Ban Treaty (CTBT) will appear before the US Senate for ratification, according to Rose Gottemoeller, Under Secretary of State for Arms Control. This was mentioned at a special event under the topic “Nuclear weapons Testing: History, Progress, Challenges”. The event was organized by the Embassy of Kazakhstan, the Embassy of Canada, Green Cross International, the Atom Project, and the Arms Control Association to mark the International Day against Nuclear Tests and to discuss the impact of the Comprehensive Nuclear-Test-Ban Treaty (CTBT).

The CTBT prohibits carrying out or participating in any nuclear weapon test explosion or any other nuclear explosion. The treaty was opened for signature at the United Nations on November 19, 1996, and on behalf of the United States government President Clinton was the first to sign it. But it has not yet entered into force. On October 13, 1999 the US Senate rejected the CTBT, which had been hastily brought to the floor without adequate preparation, or an accurate headcount of Senators. Over the past 15 years, the CTBT’s verification system has grown both quantitatively and qualitatively. As of October 2014, 183 countries have signed the treaty, and 163 have also ratified it, including Russia and all major US allies. But 44 named nuclear technology holding countries must sign and ratify the CTBT before it can enter into force. Of these 8 countries are still missing. The US is one of them, along with China, Israel, India, Pakistan, Egypt, North Korea, and Iran – not the assortment of countries one normally associates with US nonproliferation goals and democratic values.

In order to enforce the treaty, a preparatory commission, CTBT organization (CTBTO) was established in Vienna, Austria. CTBTO oversees the treaty’s entry into force and the construction and operation of the International Monitoring System (IMS). The IMS consists of 337 measurement stations all over the world. Two major classes of monitoring methods, wave and radionuclide monitoring, are used to detect signals that could indicate a possible nuclear explosion. Seismic, hydroacoustic and infrasound monitoring are part of the wave monitoring methods. Data from these measurement stations will be transmitted for analysis to the International Data Center (IDC) in Vienna through satellite links.


Seismic monitoring of nuclear tests is based not only on the depth and location of geologic events, such as earthquakes and undersea volcanic eruptions, but also on inherent differences in the way energy released by natural events and underground test explosions is coupled to the surrounding geologic medium and converted into seismic waves. When seismic waves hit a seismometer, the instrument transforms the vibration into electrical signals. The signals generated are used to detect, and locate seismic events, and to discriminate the subset of events that clearly are or could be underground nuclear explosions. There are 170 seismic stations in 76 countries around the world.


Credit: The Comprehensive Nuclear-Test-Ban Treaty Organization.

Hydro-acoustic monitoring is based on the study of sound waves in the water, which can travel great distances. When sound waves hit a hydroacoustic monitoring station, they will be registered by hydrophones. Hydrophones are sensitive underwater microphones that convert changes in water pressure to electrical signals. Data obtained from this monitoring will be used to detect and determine the location of a nuclear explosion underwater, near the ocean surface or near its coasts. There are 11 hydroacoustic monitoring stations in 8 countries globally.


The Comprehensive Nuclear-Test-Ban Treaty Organization

Infrasound monitoring stations measure very low acoustic waves (infrasound) which are inaudible to the human ear. Atmospheric and shallow underground nuclear explosions can generate these waves that cause changes in the atmospheric pressure. These changes are measures using microbarometers at the infrasound network. The microbarometer transforms the infrasound waves into electrical impulses. There are 60 infrasound monitoring stations in 35 countries globally.


Radionuclide monitoring measures the abundance of radioactive particles and gases in the air that are caused by nuclear explosions. Currently, there are 80 radionuclide stations in 27 countries worldwide. Out of the 80 IMS radionuclide stations, 40 stations have airborne radioactive particle detection capabilities. However, if the explosion is well-contained, radioactive particles will not be released. The alternative solution is measuring the radioactive noble gas isotopes instead. Because they are inert and exist in gaseous state, radioactive noble gas isotopes can be detected very far away from the explosion site. In half of the currently existing radionuclide monitoring stations, radioactive noble gases are captured and analyzed. Noble gas detection is also useful in detecting undeclared reactor and spent nuclear fuel reprocessing operations that could be engaged in producing fissile material for a clandestine nuclear weapon.

The Comprehensive Nuclear-Test-Ban Treaty Organization.


The CTBT’s monitoring systems and the International Data Center (IDC) have shown their abilities to detect nuclear tests in the three nuclear tests conducted by the Democratic People’s Republic of Korea (DPRK). According to an article, published in Physics Today, the 2006 nuclear test was detected by 22 seismic stations, including one in San Ignacio de Velasco, Bolivia, more than 17,000 Km away. The event was similar in size to a magnitude 4.1 earthquake, and its location was calculated to be within a circular area with a radius of less than 20 Km.  The 2009 test, a magnitude 4.5 event, was detected by 59 seismic stations including one 18,000 Km away in Paso Flores, Argentina. According to the CTBTO press release at the time, this increase was due to the rise in the number of operational stations as well as the larger magnitude of the 2009 test. The 2013 nuclear test, a magnitude 4.9 event, was detected by 94 seismic stations. Between 2009 and February 2014, the number of CTBTO seismic stations has further increased from 130 to 170. DPRK’s third nuclear test was also detected by infrasound and radionuclide monitoring stations in Japan and Russia.

The CTBT enjoys wide international support.  Today, over 85 percent of the CTBTO’s 337 monitoring stations are now operational and capable of detecting, locating and identifying nuclear tests from the global background of seismic and other man-made events. Entry-into-force of the CTBT will bar nuclear weapon states from testing nuclear explosive devices of hitherto unproven design, and it will make vastly more difficult, if not impossible for newer proliferant states to develop and deploy vastly more powerful thermonuclear weapons. Without the CTBT, effective enforcement of the current de-facto global moratorium on nuclear test explosions will be difficult to sustain in a globally unanimous manner. It is time for the US Senate to reconsider ratification of the treaty.