Publications: SRL: Opinion |
Late in 2007, the Seismological Society of America (SSA) and the American Geophysical Union (AGU) agreed on a joint position statement titled “Capability to Monitor the Comprehensive Nuclear-Test-Ban Treaty (CTBT).” It reaffirmed a similar joint statement issued eight years earlier, saying in essence that these two professional societies are confident that a combination of worldwide monitoring resources will meet the verification goals of the CTBT. The full statement can be found at http://www.seismosoc.org/government/position_statement.html
and in the March/April 2008 issue of Seismological Research Letters (SRL 79, 158–159). I appreciate the SRL editor’s invitation to expand here on some of the issues related to this joint statement.
The CTBT is intended to impede nuclear weapons development and as such is a major initiative in nuclear arms control, strongly supporting the endangered Non-Proliferation Treaty (NPT). It is of specialized importance to seismologists for a variety of reasons—first, because the development of seismology has been stimulated for decades by funding to improve the ability to monitor nuclear test explosions;1 and second because policymakers sometimes interact intensively with seismologists who bring their specialized skills to bear on the analysis of a particular seismic event by detecting, locating, and identifying it and estimating its yield if the event appears to have been an explosion.2 Given that seismology is recognized as the most important technology for monitoring nuclear explosions, a third reason for seismologists to pay attention to the CTBT is that ongoing professional assessments of monitoring capability are needed for serious discussion and decisions on whether this treaty is adequately verifiable.
This latter reason may be particularly salient during the next few years, as the pros and cons of the treaty are likely to be re-examined in a number of different forums.
The general goals of the CTBT are strongly supported by the general public (Simons Foundation 2007) and also by the great majority of nations, as expressed by numerous lopsided votes in the United Nations.3 But the treaty has not yet gone into effect, because although it has been signed by 178 nations (as of March 2008) since it was opened for signature in 1996, it has so far acquired only 35 of the signatures and ratifications of the 44 specific nations listed in a treaty annex as necessary for the treaty to enter into force.4 Of the recognized nuclear weapons countries, the United Kingdom, France, and Russia have signed and ratified the treaty, but China and the United States, both of which signed on to the treaty in 1996, have not ratified it. Ratification in the United States requires the advice and consent of the U.S. Senate, which debated the treaty on short notice in 1999 and voted against ratification. At the same time, there has been strong political opposition to a resumed nuclear test program in the United States. Because of this history, at present there is effectively a moratorium on nuclear testing (observed by the United States since 1992) rather than a formal treaty that has entered into force—which, for example, would have an onsite inspection program to gather information on the nature of events that treaty signatories deem sufficiently problematic.
After several years with little public attention, new interest in the CTBT has been sparked by a bipartisan group of policymakers led by George Shultz, Secretary of State under President Reagan, and more generally by consideration of the changes in U.S. policy that may accompany the next administration, recognizing that a CTBT has been a declared objective of the five Republican and four Democratic presidents from Dwight Eisenhower to Bill Clinton. In two articles in the Wall Street Journal and a forthcoming book, Shultz’s group5 recommends that, as an important step toward a world free of nuclear weapons, the United States and Russia, which together possess close to 95% of the world’s nuclear warheads, should:
Adopt a process for bringing the Comprehensive Test Ban Treaty (CTBT) into effect, which would strengthen the NPT and aid international monitoring of nuclear activities. This calls for a bipartisan review, first, to examine improvements over the past decade of the international monitoring system to identify and locate explosive underground nuclear tests in violation of the CTBT; and, second, to assess the technical progress made over the past decade in maintaining high confidence in the reliability, safety and effectiveness of the nation’s nuclear arsenal under a test ban. The Comprehensive Test Ban Treaty Organization is putting in place new monitoring stations to detect nuclear tests—an effort the U.S should urgently support even prior to ratification.
In this context it is interesting to note briefly how monitoring capability was characterized in the U.S. Senate debate of October 1999. Two Senate committees held hearings on short notice that month; neither one had testimony from experts in explosion monitoring.6 But numerous statements concerning monitoring were made during the floor debate, including some that seem substantially incorrect. A repeated statement was that “the United States cannot detect nuclear explosions below a few kilotons of yield.” This may have been an accurate statement in about 1958 when CTBT negotiations began, but 50 years later, as reviewed by Sykes (2002), we can monitor better than this by orders of magnitude. Successful methods of discriminating between earthquakes and underground explosions, based on the analysis of teleseismic body waves and surface waves, were developed in the 1960s and improved in later decades. To reliably monitor events smaller than magnitude 4, regional seismic signals are needed. Several methods of analyzing spectral ratios of the regional waves Pn, Pg, Sn, and Lg have been developed to discriminate between earthquakes and explosions (Taylor et al. 2002). Scientists continue to gain experience in determining which spectral ratios are most successful in different regions. This work can be difficult simply because of the great number of small earthquakes and mine blasts that require some level of attention in the effort to monitor globally for small nuclear explosions. But there is demonstrated success, and no fundamental difficulties exist provided the necessary resources are available to do the work.
More than one speaker in the Senate debate of 1999 claimed that “a 70-kiloton test can be made to look like a 1-kiloton test, which the CTBT monitoring system will not be able to detect.” It is widely recognized that signals from a test conducted underground in a sufficiently large and deep cavity can have their seismic signals reduced by a factor of 70, but the concept has been validated only at subkiloton yield and faces practical difficulties at yields above a few kilotons, even without trying to hide the operation.7
In light of the Shultz et al. recommendation quoted above on the need to examine improvements in monitoring capability, and also in light of the way in which monitoring capability was characterized in the first U.S. Senate debate on CTBT ratification, SSA members may wish to know of recent reports and technical papers that provide some detailed information and assessments on monitoring capability.
Our SSA-AGU joint statement of December 2007 was suitable for its intended purpose, a minor revision of the short statement made originally in 1999—but today it may be out of date in its references to a detection capability at the magnitude 4 level. In my opinion, we can do much better than this in many parts of the world.
It is also my opinion that SSA members play a very important role in assessments of monitoring capability. Indeed, our professional activities collectively include work that will impact some of the most important decisions our human society will ever make. Whether you, the reader, regard nuclear weapons as part of the solution or part of the problem in maintaining a more peaceful world, we can expect that policymakers and interested members of the public will occasionally look to us as seismologists for technical advice. I therefore hope that we as members of the SSA will spend some time getting up to speed on issues related to seismic monitoring of nuclear explosions.
Barker, B., M. Clark, P. Davis, M. Fisk, M. Hedlin, H. Israelsson, V. Khalturin, W.-Y. Kim, K. McLaughlin, C. Meade, J. Murphy, R. North, J. Orcutt, C. Powell, P. G. Richards, R. Stead, J. Stevens, F. Vernon, T. Wallace (1998). Seismology: Monitoring nuclear tests. Science 281, 1,967–1,968.
Hafemeister, D. (2007). Progress in CTBT monitoring since its 1999 Senate defeat. Science and Global Security 15, 151–183.
Hafemeister, D. (forthcoming). CTBT is effectively verifiable. Arms Control Today.
Jeanloz, R. (forthcoming). Comprehensive Nuclear-Test-Ban Treaty and U.S. security. In Reykjavik Revisited: Steps Toward a World Free of Nuclear Weapons. Proceedings of the October 2007 Hoover Institution Conference. to be published by Hoover Press (http://www.hooverpress.org).
Kim, W.-Y., and P. G. Richards (2007). North Korean nuclear test: Seismic discrimination at low yield. EOS, Transactions, American Geophysical Union 88 (14), 157, 161.
Kværna, T., F. Ringdal, and U. Baadshaug (2007). North Korea’s nuclear test: The capability for seismic monitoring of the North Korea test site. Seismological Research Letters 78, 487–497.
Medalia, J. (2007). Nuclear Weapons: Comprehensive Test Ban Treaty. CRS Report for Congress, December 19 (available at http://www.fas.org/sgp/crs/nuke/RL33548.pdf).
Medalia, J. (2008). Comprehensive Nuclear-Test-Ban Treaty: Issues and Arguments. CRS Report for Congress, February 28 (available at http://www.fas.org/sgp/crs/nuke/RL34394.pdf).
National Academy of Sciences (NAS) (2002). Technical Issues Related to the Comprehensive Nuclear-Test-Ban Treaty. Washington, DC: National Academy of Sciences, National Academy Press (available as pdf files via a search on “technical comprehensive” at http://www.nap.edu).
Simons Foundation (2007). Global Public Opinion on Nuclear Weapons. http://www.angusreidstrategies.com/uploads/pages/pdfs/Simons%20Report.pdf.
Sykes, L. R. (2002). Four decades of progress in seismic identification help verify the CTBT. EOS, Transactions, American Geophysical Union 83 (44), 497, 500.
Taylor, S., A. Velasco, H. Hartse, W. S. Philips, W. R. Walter, and A. Rodgers (2002). Amplitude corrections for regional discrimination. Pure and Applied Geophysics 159, 623–650.
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Posted: 01 May 2008