Monitoring Nuclear Explosions: Why, How, and What do We Learn
Paul G. Richards
Mellon Professor of the Natural Sciences
Lamont-Doherty Earth Observatory
Columbia University
The capability to monitor nuclear explosions has for decades been built up by the United States and other countries -- to gain information on the weapons development of potential adversaries, and to support initiatives in nuclear arms control. We know there have been 2000 nuclear test explosions since World War II. Most were thousands of times bigger than the largest conventional bombs. A few were millions of times larger. The Earth Sciences, particularly seismology, have provided the principal monitoring technologies, and have in turn been significantly influenced by the need for improvements in monitoring capability.
This public lecture will describe work being done to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty, now signed by 170 countries. This treaty is still not in effect, but has turned in recent years into a nuclear testing moratorium.
Assessments of monitoring capability have always been difficult to conduct without political overtones, but it seems clear that monitoring is far better today than was envisaged during the treaty negotiations, and capability to monitor down to lower and lower yields will continue to improve.
About the Lecturer
My work has two strands, one as a scientist (seismology), and the other as a technical expert in specific issues of national security.
I started out in research in the 1960's with a mathematics background, and an interest primarily in the theory of seismic wave propagation. This led to new methods for understanding how processes of diffraction, attenuation and scattering affect the recorded shapes of seismic waves. From such scientific work we learn details of the Earth's internal structure, and details of fault motion in earthquakes as rock spontaneously fractures and moves to reduce stress.
In 1984 I took a national service leave from Columbia and worked for 12 months in Washington with the US Arms Control and Disarmament Agency, joining the group that wrote the President's report to Congress on Soviet Arms Control violations. Since the mid-1980s much of my work has focused on the use of seismological methods to study nuclear explosions and their implications in both the scientific and political worlds. There have been about 2000 such explosions (1500 underground), carried out in programs of weapons development and also to study the effects of nuclear weapons on military hardware. How underground explosions are detected, identified and located - and how big they are - are often subjects of intense debate in forums that seek to assess the capability of nuclear weapons deployed by potential adversaries of the United States. These issues also are critical in evaluating present or prospective arms-control treaties. In 1993 I took another 12-month national service leave and again joined US ACDA, this time working on technical issues associated with monitoring the Comprehensive Test Ban Treaty. I participated in the Geneva and Washington negotiations for this treaty, for which the text was finalized in 1996.
A side effect of the end of the Cold War has been new opportunities to acquire seismic data on earthquakes and explosions in Russia, China, and Central Asia. Together with my colleague Won-Young Kim at Lamont, I have had projects in Kazakhstan since 1991 with scientists working in that country. We use superb facilities in Central Asia originally built by the Soviet military to monitor underground nuclear explosions carried out by the US.
There is ongoing discussion of the Comprehensive Test Ban Treaty and the associated Non-Proliferation Treaty. The CTBT has been signed by 170 countries, and the NPT by over 180. Both are in deep trouble following the decision of the US Senate on October 13 1999 not give advice and consent to CTBT ratification by the United States. Seismology is a key technology that should guide part of these debates, but the technical material (assessments of monitoring capability) is often misrepresented in political arenas.
In recent years I have worked with others to improve the accuracy with which seismic events (earthquakes, explosions) are routinely located by organizations engaged in treaty monitoring. Improvements in location accuracy can be expected also to lead to insight into the earthquake process, specifically into how neighboring earthquakes are related to each other.
I retain a strong interest in the scientific study of seismic signals, and in 1996, together with Xiaodong Song, discovered seismological evidence that the inner core of the Earth is rotating eastwards with respect to the mantle and crust. Since the inner core is about the size of the Moon, the claim that it is moving inside the Earth at a rate perceptible on human time scales has many scientific implications.
More Information
http://www.ldeo.columbia.edu/~richards/
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