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January 6, 1997

Scientists convene in San Francisco to discuss Comprehensive Test Ban Treaty

Seismologist Thorne Lay (photo) envisions his two-year-old son growing up in a world with no more nuclear explosions. If scientists can devise reliable ways to monitor compliance with the new Comprehensive Test Ban Treaty, Lay's vision very well may come to pass.

Researchers from a sweeping array of disciplines gathered on December 15 at the fall meeting of the American Geophysical Union in San Francisco to take stock of the extraordinary scientific challenges posed by the Comprehensive Test Ban Treaty (CTBT). Lay, a professor of earth sciences at UCSC, cochaired the daylong session of talks with Steven Bratt, program manager for the CTBT's International Data Centre.

Speakers explored the progress to date toward meeting the rigorous verification demands of the CTBT and the research issues that scientists still must address. More than 140 nations have signed the treaty, which was opened for signature in September at the United Nations. Although the treaty will not go into force for at least two years, pending ratification within each country, it requires that a verification regime be put into place in the interim. The clearinghouse for data from the verification networks will be the International Data Centre (IDC), to be established in Vienna. Bratt is part of an international team that has set up a prototype of the IDC in Arlington, Virginia.

When the IDC is fully operational, up to 10 gigabytes of scientific data--equivalent to 10,000 floppy disks--will stream into the center every day. "These data will be unique and obviously will have many valuable scientific uses," Bratt says. "But we will need to focus on their main use, which is verification. We need to engage the best and the brightest minds we have to help solve the serious problem of how to most efficiently gather and process all of that information."

The CTBT's verification regime covers four main types of data:

-- Seismic. The most central of the monitoring technologies, seismology is critical for detecting vibrations that emanate from underground nuclear tests. A state-of-the-art global network of 50 primary and 120 auxiliary seismic stations will ceaselessly record all signals from earthquakes, explosions, mining blasts, oil-exploration tests, and other groundshaking events. Stations will be installed or upgraded in many parts of the world, including China, Russia, the Middle East, and other sensitive regions, to support the new CTBT monitoring requirements.

-- Infrasound. A new 60-station infrasound network, the first of its kind since nuclear testing in the atmosphere was banned in 1963, will be critical for detecting and deterring such testing in the future. In addition to its role in the CTBT, this network should provide valuable information about phenomena such as volcanic eruptions, meteors, and atmospheric "baroms"--bizarre roaring sound waves in polar regions.

-- Hydroacoustic. Eleven sensitive listening posts in the world's oceans will monitor for the shock waves produced by underwater nuclear explosions. Expected scientific benefits include detailed sonic pictures of submarine earthquakes, volcanoes, and seafloor collapses.

-- Radionuclear. Eighty stations will regularly collect air samples to search for particles and gases that can escape from nuclear tests. Unlike the other three technologies, where detection occurs at the speed of sound, it can take days for such substances to drift within range of a radionuclide detector.

The international sharing of such a wide range of data, some of it potentially incriminating, is unprecedented in the arms-control arena and perhaps in all of science. The only comparable area, Lay notes, is the free exchange of data on atmospheric weather patterns. The CTBT research agreements arose largely because the scientific community convinced United Nations negotiators that the monitoring network was feasible. Even so, much work remains. The seismological challenges alone, says Lay, are daunting.

While the treaty calls for a total ban on nuclear testing, there is a threshold beneath which the seismic network will be unable to detect tiny events, Lay says. However, much of the research by network designers is driven by the U.S. objective of detecting explosions as small as a few kilotons "evasively tested," meaning that the testers devise some way to prevent the explosion from vibrating the surrounding rock as strongly. Suspending the device within a large subterranean cavity is one such technique. To unveil all such explosions, says Lay, "We'd have to be able to look everywhere in the world for a magnitude 2.5 event, detect it, and discriminate between an earthquake, nuclear test, mining blast, or some other event. That's a staggering objective."

Initially at least, the CTBT's International Monitoring System will have as its goal the worldwide detection of all events of magnitude 4 or greater--equivalent to the seismic waves triggered by a one-kiloton device fully coupled with the ground around it. Lay terms this a "major advance" over current capabilities.

The ultimate goal, says Bratt, is to make it as difficult as possible for a nuclear event to slip through the monitoring system's cracks. If the seismic network has a 90 percent probability of detecting a magnitude 4 event, it might have a 50-50 chance to hear an explosion at some lower threshold--perhaps enough to deter potential violators. If the testers set off the explosion in a large cavity, they increase the odds that telltale radionuclides will escape into the atmosphere from cracks in the ground. "These all are risks that an evader must evaluate," Bratt says. "We'll be making it very risky for someone to attempt to evade and be successful."

The IDC in Vienna will exist solely to process all of the incoming data and characterize each event as thoroughly as possible. However, it will be up to the signatory countries to decide whether to bring an accusation before the United Nations and demand an on-site inspection. "A country can ask the IDC to carefully reanalyze a particular event," Bratt says. "However, even if we think that it has feathers, a yellow bill, and webbed feet, we can't call it a duck." In that way, he says, the IDC will remain a neutral scientific entity.

Technologically advanced countries, especially those with global interests in national security, will continue to rely upon their own data resources to augment any potential detections from the IDC. These include enhanced networks of instruments already present in the CTBT Verification Regime, such as denser arrays of seismic stations in key parts of the world or strategically positioned hydrophones. Countries will continue to use many other means that negotiators opted not to include in the final CTBT, such as satellite imagery, detection of electromagnetic pulses, and monitoring of effluents in rivers and coastal zones.

The U.S. Department of Defense budgeted $28 million in fiscal year 1997 for continued deployment of the International Monitoring System. Of that budget, $8.8 million was devoted to studies related to basic CTBT monitoring research. Scientists submitted their applications for those funds in November.

--Robert Irion

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