Department Seal Benefits to the U.S. Derived From the
CTBT International Monitoring System

Fact Sheet released by the Bureau of Arms Control,
U.S. Department of State, Washington, DC, October 8, 1999

The CTBT verification regime has been configured to provide information of importance to meet our monitoring and verification requirements.

The International Monitoring System (IMS) consists of four global networks (seismic, radionuclide, hydroacoustic and infrasound) capable of supporting the functions of detection, location, and identification of explosions in different physical environments. The networks' synergistic capabilities and global distribution -- over 300 stations and facilities -- complement one another to support monitoring and verification goals.

IMS site preparation and station installation have been delayed in part due to the necessity for host-country agreements with the Provisional Technical Secretariat (PTS) and the development and acquisition of equipment. Nevertheless, the U.S. Government is confident that IMS installation is proceeding apace. The PTS projects that more than 160 IMS stations will be reporting data to the International Data Center by the end of 2000. Further, the U.S. Government is confident that U.S. ratification of the treaty will facilitate and accelerate the IMS installation program.


  • While some parts of the IMS are part of the U.S. monitoring system (U.S. Atomic Energy Detection System) and others are not, all data from the CTBT verification regime will be utilized to support U.S. monitoring and verification requirements.

  • The CTBT provides the U.S. with access to additional monitoring stations to which we would not otherwise have access.

  • The Treaty will provide monitoring coverage of key areas of interest to the United States. For example, the CTBT requires the installation or upgrade of 31 stations in Russia, 11 stations in China, and 17 stations in the Middle East.

  • In addition to new stations that will be built under the Treaty, many existing seismic stations will be upgraded to meet Treaty specifications that will ensure conformity of data for all stations in the system.

  • With planned improvements in U.S. national technical capabilities and the international sensors mandated by the Treaty, the U.S. will have more resources with which to monitor nuclear testing and address compliance concerns.

  • The CTBT's International Data Center will process IMS data for all Parties so at their discretion they can base their national compliance decisions on reliable and useful products.

  • The infrastructure being established for the conduct of on-site inspections, used to clarify the nature of an ambiguous event, will deter potential violators who could not then be assured of their ability to carry out evasive testing. Further, this element of the Treaty verification regime provides access to locations not otherwise open for inspections and thus provides the means to satisfy a U.S. monitoring and verification objective.
The value of the IMS has been underscored by several recent incidents:
  • Six IMS stations detected the 1997 Kara Sea event near the Russian Novaya Zemlya test site. Data from some of these stations assisted the USG in concluding that there was an earthquake southeast of the test site, that the seismic event was not nuclear, and that the event was not associated with testing activities.

  • More than 60 IMS stations reported data on India's May 11, 1998 and Pakistan's May 28, 1998 tests. Over 50 stations reported data on Pakistan's May 30, 1998 test. The detection and location capability on the Indian subcontinent will be improved by the installation of new seismic stations mandated by the Treaty -- stations that will help detect events at even lower levels in this area.

  • As we monitor for testing at lower levels, regional capabilities will become more important, even in areas not currently considered central to U.S. monitoring needs. Our ability to detect low yield testing will continue to improve with implementation of the enhanced U.S. collection network, completion of the IMS, experience in dealing with a more robust CTBT operating system, and an increased understanding of regional geologies.
Specifically, the IMS includes:
  • Fifty primary and 120 auxiliary seismic stations that monitor seismic signals propagating through the earth from natural events (earthquakes) and man-made events (mining blasts and explosions);
  • Eighty radionuclide stations that pick up traces of radioactivity following a nuclear explosion in the atmosphere or leaked from an underground nuclear test;
  • Six hydroacoustic stations and 5 "T-Phase" hydroacoustic stations to detect explosions on the ocean surface and under the water; and
  • Sixty infrasound stations to provide evidence of a possible atmospheric explosion by detecting sound pressure waves in the atmosphere.
Of these totals, 262 Treaty-required stations will further enhance U.S. verification capabilities:
  • Thirty-one primary seismic and 116 auxiliary seismic stations;
  • Fifty-seven radionuclide stations;
  • Eight hydrophone/T-Phase stations; and
  • Fifty infrasound stations.
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