Seismology and CTBT Verification

It is well-known that the design and production of nuclear weapons required major efforts in scientific research and engineering, with a supporting infrastructure of weapons laboratories. Less well-known, is that scientific research and development have also played an important role in nuclear arms control. In this paper, my purpose is to explain the role of seismology in treaty verification; to describe what seismology (and associated infrastructures) can and cannot do using monitoring systems now in place; and to give a sense of what can be expected with likely future improvements. Seismology is the study of how the ground moves, not just for strong earthquakes like that which severely damaged the Stanford University campus in October 1989, but for ground motions that can be detected even a billion times smaller, caused by earthquakes and explosions which may originate on the other side of the world. Each earthquake or explosion sends out a mixture of different types of seismic waves, and for decades seismologists have been interpreting these signals in order to characterize the seismic source. Seismology has overlapping infrastructures to study the internal structure of our planet, to study earthquake hazard, and to monitor explosions. Seismology became particularly important as a monitoring technology following the Atmospheric Test Ban Treaty of 1963, because nuclear testing moved underground and was found to generate easily-detectable seismic signals, observed all over the world for most nuclear tests. On average, about one nuclear explosion a week was carried out underground from the early 1960's to the early 1990's. Underground nuclear testing became an integral part of the process by which new nuclear weapons were designed and certified as ready for deployment --and seismology was built up as a practical science because it became a principal means to learn of the developing nuclear weapons capability of a potential adversary. It was also recognized to be an arms control technology for monitoring compliance with an eventual ban on nuclear testing.