THE COMPREHENSIVE NUCLEAR TEST BAN TREATY AND SEISMOLOGICAL RESEARCH
Even as I write, the U.S. Senate is conducting hearings on the issue of ratification of the Comprehensive Nuclear Test Ban Treaty (CTBT), signed by President Clinton on September 24, 1996, and by more than 140 other nations subsequently. Building upon several previous bilateral and multilateral treaties that have partially constrained nuclear weapons testing since 1963, the CTBT mandates that "Each State Party undertakes not to carry out any nuclear weapon test explosion or any other nuclear explosion, and to prohibit and prevent any such nuclear explosion at any place under its jurisdiction or control" (Article 1.1, Comprehensive Nuclear Test Ban Treaty). If globally embraced, the CTBT will shut the door on the nuclear weapons testing era after 52 years and more than 2090 nuclear explosions around the world. As the Senate considers the many political, technical and philosophical issues that frame this particular arms control endeavor, it is important for seismologists to reflect upon the critical role played by our discipline in past and future nuclear testing treaty monitoring efforts.
The flourishing of seismology as a quantitative science has been closely coupled to the political context of global monitoring of underground nuclear tests (revealed by the elastic waves generated at the source which propagate as diagnostic signals to large distances). There have been more than 1570 such tests, commencing with the first contained underground explosion, Rainier, detonated on September 19, 1957, at the Nevada Test Site. Monitoring active nuclear testing programs of other countries sustained significant military and intelligence interest in seismological capabilities for more than 40 years and motivated large investments in instrumentation, research programs, education, and general maturation of the discipline. Our field would certainly be much smaller and less advanced were it not for this societal application (and the relatively deep pockets of the defense arena).
Does the CTBT imply a major transition for research funding and job opportunities in seismology? Clearly, some aspects will be different under a CTBT, as there will no longer be 3 to 4 underground nuclear tests each month around the world to be detected and quantified by seismologists. The predominant role for seismology will instead involve screening of all detected events to ensure that none of them are surreptitious nuclear explosions in violation of the Treaty. Applying seismology to detect nuclear explosions anywhere in the world is not a new role (there has clearly always been interest in doing so), but it is intrinsically an arms control issue rather than a weapons assessment issue. Nonetheless, it is a long-term effort that requires ample seismological expertise, particularly for addressing the inevitable 'problem' events that arise when routine procedures fail to provide unambiguous results. One of the underlying challenges for CTBT monitoring will be to sustain the resource commitments to enduring seismological operations that, ideally, never find actual treaty violations (all of the signals can then be viewed as background noise of no intrinsic interest-of course we hope to see the data passed on to other applications where the 'noise', such as natural earthquake vibrations, can be used to address other national and scientific concerns).
The zero-yield implication of the CTBT wording is in tension with the finite resources available for global seismological monitoring as well as with the intrinsic limitations of seismic methodologies for locating and identifying sources. Each nation must therefore define acceptable CTBT monitoring levels commensurate with their national security perspectives and then ensure adequate capabilities to achieve those levels. The U.S. has specified a national objective of "monitoring the CTBT to a level of a few kilotons, evasively tested, in key areas of the world" (this is the unclassified terminology). This implies an assessment that sub-kiloton level explosions are not of nuclear weapons development significance; a pragmatic (and contentious) technical decision. Of course, there will be interest in detecting any smaller events if possible, but the monitoring system will be designed not to miss any events at the designated level. Evasive testing could involve detonation of a device in a pre-existing air-filled cavity (decoupling), which can significantly reduce the amplitude of seismic waves generated by the event. While translation of this monitoring objective into specific seismological magnitude thresholds is regionally dependent, event detection and identification thresholds as low as about magnitude 2.5 are required for the limited areas where evasive decoupling is viable. Fully coupled explosions of 1 kiloton yield produce seismic magnitudes of from 3.9 to 4.5 for different source regions (based on the modest number of actual test sites for which these magnitude levels have been inferred), so this is approximately the global threshold intended for reliable event detection and identification in areas where decoupling is not a concern. To put these numbers in perspective, current unclassified global seismic catalogs for continental areas, such as the Bulletin of the International Seismological Centre, are not complete at the magnitude 4.5 level, so improved global earthquake catalogs will be needed. Improved, uniform global seismic catalogs have many potential benefits for other applications such as earthquake hazard reduction and earth structure investigations.
While global seismic monitoring capabilities are quite advanced, in part as a result of past treaty monitoring investments, the CTBT does define challenging new goals for U.S. operations. As seismic magnitudes dip down to magnitude 4.0 and lower, it becomes increasingly difficult to detect, locate and identify events exclusively using teleseismic signals with low signal-to-noise ratios. Thus, regional seismic phases must be exploited, and these are acutely sensitive to crustal heterogeneity. While there has been substantial progress in quantifying regional phases in some regions of the world, the global coverage required for the CTBT, the possibility of evasively coupled events of very low magnitudes, and the possibility of events obscured by simultaneous quarry blasts, mine bursts, or other seismic disturbances, define substantial challenges for characterizing seismic signals in many regions that have not yet been studied in detail. The CTBT text (available in PDF format from http://www.unog.ch/frames/disarm/distreat/warfare.htm) is extraordinary among nuclear testing treaties in its extensive description of an International Monitoring System (IMS) that is to be established for the monitoring effort. This includes a global 50 station Primary seismic network providing continuous real time data to an International Data Center (now being established in Vienna) and a 120 station Auxiliary network with dial-up access. I do not believe there is any other international treaty in which seismology is explicitly recognized to have such a critical roll. As many of the planned stations are not yet deployed, there will be several years of vigorous calibration and analysis of signals at each station for regional and teleseismic distances that could sustain many research seismologists in the National Laboratories, private industry and academia.
The projected capabilities of the International Seismic Monitoring System, augmented by additional existing and newly deployed National Technical Means, should provide the seismic data required to achieve the U.S. monitoring goals. This is doable effort, but one that requires a steadfast commitment and utilization of multiple seismological capabilities in the nation. However, there are numerous technical issues that require basic research in parallel with the systematic network calibration and analysis effort. These include improving our knowledge of three-dimensional lithospheric structure in areas of concern; improved seismic wave propagation capabilities for quantifying regional seismic signals; improved theoretical and experimental understanding of seismic discriminants that provide critical event identification; and enhanced event location methods using regional data. As the IMS will include hydroacoustic, infrasonic, and radionuclide networks, and the U.S. will continue to utilize satellite imaging capabilities and other assets, there is also a basic need for research to exploit synergies provided by availability of multiple data types from global arrays (for example, how best to use infrasonic and seismic signals to characterize quarry and mining blasts). This is not a particularly contentious opinion, as even President Clinton has stated in his August 11, 1995 White House Press Release, "I recognize that our present monitoring systems will not detect with high confidence very low-yield tests. Therefore, I am committed to pursuing a comprehensive research and development program to improve our treaty monitoring capabilities and operations." There are some voices in the seismological community that downplay the need for additional basic research, but a sober assessment of the overall CTBT monitoring challenge does provide a compelling basis for sustaining a broadly based research effort. But, is the U.S. responding to this need?
A major concern addressed in a recent National Research Council report, for which I served as panel chairman, is that federal research funding for seismological efforts that support U.S. CTBT monitoring capabilities is actually declining significantly, even while the Treaty is being considered for ratification. In FY 1995 and FY 1996 there was about $12 million in external research funding (mainly from the Department of Defense and Department of Energy) that supported university and private contractor research (largely seismological) in support of CTBT monitoring. In FY 1997 the amount plummeted to less that $6 million, as the CTBT was being signed, and there was about a 30% reduction in active external research contracts. The Department of Energy, only begrudgingly involved in external funding of CTBT research at all, has no commitment to future programs. This leaves the newly constituted Nuclear Treaty Program Office (NTPO) of the Department of Defense as the only well-defined research program with significant funding for CTBT research by industry and academia (the NTPO research program has an FY 1998 budget of $8.8 million to support external research in seismology, hydroacoustics, infrasonics and radionuclides). Given that we are at a critical stage in the CTBT process, it is clear to me that the NTPO research budget is significantly too low to rapidly and comprehensively establish the Treaty monitoring capability defined by our national objectives. The NRC report identifies fundamental research in all of the monitoring technologies that should be performed to enhance and enable CTBT verification, and it also concludes that the current external funding levels are significantly too low. In my opinion, ratification of the Treaty should proceed because I think the key problems are all solvable, but there should be a parallel federal government follow-through on President Clinton's commitment to a comprehensive R&D program.
Why is it that funding is contracting even in the face of the urgent political agenda that sent the CTBT to the Senate for advice and consent even in advance of full deployment and validation of the IMS? There is no question that part of the explanation is provided by the fiscal climate in Washington, which brought about contraction of many research budgets in recent years. However, relative to the multi-billion dollar levels of funding for other nuclear weapons related arms control efforts, the approximately $100 million overall budget for CTBT activities is modest. and the external research program funding is certainly at the round-off error level. I have been unimpressed by DOE attitudes toward external research funding and the administrative reluctance to define and commit to any multi-year engagement with seismological researchers in industry and academia. While certainly sustaining excellent internal seismological research capabilities, the National Labs tend not to foster creative breakthrough discoveries, the hallmark of University research in this and other areas. The DoD program has undergone much internal turmoil and restructuring, which have not been conducive to budgetary growth. I also believe that the seismological research community has sometimes engaged in self-serving political activities that have not been as responsive to the CTBT monitoring effort as they should have been. Now, however, the NTPO program has the opportunity and potential stability necessary to expand the research effort as needed during the next few years while the national and international CTBT monitoring system is developed and implemented. I encourage seismologists to become familiar with the underlying issues and to support the growth of the CTBT research program, as there is still much that our discipline has to offer in enhanced seismological understanding and capabilities, as well as in training personnel that will contribute to the long-term elimination of nuclear testing. Recognizing that there is a sea-change in the context and goals of CTBT monitoring, we researchers must recognize the need to address focused needs of the monitoring system, but program managers must also sustain the flexibility to encourage creative breakthroughs and advances on a broad range of related topics, as has proved so successful in advancing our capabilities to where they are today. Seismologists can certainly reflect positively on our past contributions to this important societal issue, but there are many challenging problems that need to be resolved as we move into a new millennium that hopefully will be free of nuclear explosions.
To send a letter to the editor regarding this opinion or to write your own opinion, contact Editor John Ebel by email or telephone him at (617) 552-8300.
Posted: 26 February 1998