False Accusations, Undetected Tests and Implications for the CTB Treaty
van der Vink, Gregory, Park, Jeffrey, Allen, Richard, Wallace, Terry, Hennet, Christel, Arms Control Today
Recent events have raised concerns about the ability of the United States to monitor compliance with the Comprehensive Test Ban Treaty (CTBT). The false accusation by the Clinton administration last year of a Russian underground nuclear weapons test at Novaya Zemlya, the surprise resumption of nuclear testing in May by India, and the lack of seismic signals from some of the announced Indian and Pakistani tests have been attributed to failures of the U.S. intelligence community, and have been presented as evidence that the CTBT cannot be verified and should not be ratified by the United States. An analysis of these events reveals, however, that while there may be deficiencies in intelligence procedures, the technical capability of the United States to detect underground nuclear weapons tests is remarkably good. Given that the objective of the CTBT is to deter proliferation by preventing the development of more advanced nuclear weapons, recent events demonstrate that the evolving verification regime can effectively monitor compliance with that goal.
While the treaty's International Monitoring System (IMS) is preparing to meet the routine requirements for CTBT verification, it is only one source of data that can be used to detect clandestine underground nuclear weapons tests. In addition to the global network used by the United States for national monitoring purposes (which shares some IMS stations), in many areas of the world seismic stations installed for scientific purposes such as studying earthquakes provide a capability that far exceeds that of the treaty's monitoring system. The intelligence community could take advantage of these resources to further improve U.S. monitoring capabilities. As more such data becomes available and global communications continue to improve, it now appears that the basic tenets of "good science"-consideration of all data, independent review and open access-may also, in many cases of relevance, be the new basic tenets for good treaty monitoring.
Monitoring the Test Ban
Since 1963, the United States has been monitoring the Limited Test Ban Treaty, which prohibits the testing of nuclear weapons in the atmosphere, in space and underwater. With the possible exception of one ambiguous event in 1979, we have high confidence in the global accounting of all above-ground tests. The monitoring of testing underground has been the greatest technical challenge, and one that has consumed, either sincerely or disingenuously, most of the negotiations during the four decades the world has pursued a comprehensive test ban.
For underground explosions, the principal monitoring burden falls upon seismology. The seismic signal from an explosion must be detected, the source of the resulting seismic waves must be located by combining data from several seismic stations, and the seismic signal must be recognized as originating from an explosion rather than a naturally occurring earthquake. It is therefore the capability of the seismic monitoring system that defines the baseline capability of the CTBT verification system.
The IMS and its associated International Data Center (IDC) began prototype operations in January 1995. When fully operational, the system's seismic monitoring network will consist of 50 primary stations and 120 auxiliary stations. The primary stations are used to detect seismic events, and the auxiliary stations are used to help determine an event's location, magnitude and seismic characteristics. The network is expected to detect all seismic events anywhere in the world of magnitude 4 or larger on the Richter scale, and to locate those events within a 1,000-square-kilometer error ellipse, the maximum area permitted for an on-site inspection under the terms of the treaty. In addition, the IMS is supplemented with a radionuclide monitoring network, a hydroacoustic network to monitor underwater disturbances, an atmospheric infrasound network, and an on-site inspection mechanism. …