Experts Say New Sensing Tools Could Help Ease Concerns on Nuclear Test-Ban Treaty

Technological advances in recent years have greatly enhanced prospects for international watchdogs to detect even small covert nuclear tests, according to a study whose findings address one of the U.S. Senate’s concerns from 1999, when it voted against ratification of the Comprehensive Nuclear Test-Ban Treaty

A global system of sensors that monitor the Earth’s rocky crust, oceans and atmosphere for tell-tale signs of nuclear explosions has moved from prototype systems in the 1990s to nearly full implementation today. System managers, meanwhile, have launched a process to engage independent scientists and engineers on an ongoing basis to help keep the technology and analysis techniques robust and innovative, study leaders told a 13 July gathering sponsored by the AAAS Center for Science, Technology and Security Policy and the Center for Strategic and International Studies (CSIS).


Ola Dahlman
[Photo © Kathy Sawyer]

The International Scientific Study, the most comprehensive international evaluation of verification capabilities to date, was initiated early last year in part because political interest in the treaty was rising again, Ola Dahlman of Sweden, a seismologist, long-time verification expert, and chairman of the study, told an audience of some 200 at the three-hour luncheon session in the Hart Senate Office Building.

President Barack Obama has expressed support for the treaty and said his administration would pursue ratification "aggressively and immediately."

The treaty seeks to ban all nuclear explosions. Supporters of ratification say that, among other things, by prohibiting testing it would prevent other states from developing increasingly advanced nuclear weapons. At the same time, some say, it would lock in a U.S. advantage that could be maintained without testing. A moratorium on US testing has been in place since 1992, and a Russian moratorium began in 1990.

Treaty opponents argue that verification will be insufficient , that other nations may manage to test without detection, and that in any case some de facto nuclear weapons states will never ratify the treaty. Some critics also view testing as the best way to maintain the credibility of the U.S. nuclear arsenal.

The United States signed the treaty in 1996, but the U.S. Senate declined to ratify it. Though 148 countries have ratified it, the agreement will enter into force only after nine key hold-out nations—including China, Egypt, North Korea, Indonesia, Iran, Israel, Pakistan and India as well as the United States—follow suit.

Dahlman said the new study took a networking approach, similar to that of the Intergovernmental Panel on Climate Change, which enabled it to engage a large number of scientists quickly. Some 600 researchers from 99 countries including India, Pakistan, Indonesia, Iran and China participated.

The majority "had not had previous experience with the treaty. So they’ve created quite a large network of scientists," said Jenifer Mackby, a Fellow in the CSIS International Security Program.

Dahlman said the biggest surprise at the conference was in the rich harvest of high-quality research posters. While he and his colleagues had hoped for a few dozen or perhaps 100, he said, they received "more than 200 posters from 60 countries and... [with] a fairly even distribution among the different technologies."

The primary verification technologies, most of which have utility for multiple purposes in addition to nuclear monitoring, are: seismology (for detecting events underground and underwater); hydroacoustics (for detecting events underwater); infrasound (for detecting events in the atmosphere); and radionuclide monitoring (which samples the air for radioactive particles and gases released in nuclear events and can provide "smoking gun" evidence that an event was nuclear and not an earthquake, an incoming meteor, a mining explosion, or other natural or human-caused disturbances).

The instruments are dispersed among 228 stations (out of a planned total of 337 facilities) that make up the treaty’s International Monitoring System. They are managed from the headquarters of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), based in Vienna, Austria. The study findings were first presented at a conference at the Hofburg Palace in June.

Seismic stations are currently providing data on about a hundred events a day worldwide, almost all of them earthquakes, scientists told the gathering. Depending on the circumstances, the system can detect explosions equivalent to one kiloton of TNT and at certain places possibly even as small as 10 tons, according to some experts at the CSIS/AAAS event. And it can pinpoint the location of an event within a margin of error of about 10 miles.

The speakers noted the dramatic improvement demonstrated after North Korea’s recent activities: In October 2006, 22 seismic stations recorded that country’s nuclear test explosion. In May this year, the number of stations detecting a similar North Korean burst had grown to 61.

The hydroacoustic network, nearing completion, showed its extreme sensitivity in September last year, when about 44 pounds of TNT were detonated off the coast of Japan and the ocean-borne waves were picked up by sensors more than 3,700 miles away off the coast of Chile, reported physicist Jay Zucca, acting program director for nonproliferation at the Lawrence Livermore National Laboratory in California.

During a spirited question-and-answer period, audience members asked about the system’s shortcomings, especially the possibility that a would-be cheater could fool the monitors by setting off a device large enough to be militarily significant but too small—and too well-hidden, say, in a subterranean cavern—to be detected. (In the case of North Korea’s latest nuclear test, it was noted, sensors did not detect radioactive gases that often leak from an underground test. However, had the treaty been in effect, an on-site inspection undertaken under treaty auspices would likely have detected such gases.)

"It’s a key question, of course—how good is the system?" Dahlman responded. He cited the system’s demonstrated ability, at least in the Northern Hemisphere, to "see things, with a 90% probability, down to magnitude 3.2 to 3.4." Referring to the assumption that a magnitude 4 disturbance [a light earthquake] equates to a one-kiloton explosion, he added, "this is almost a factor of 10 below that."

Several speakers mentioned that the international monitoring system is also augmented by the assets of individual nations, such as U.S. satellites.

Dahlman suggested turning the question around: "What risks are you prepared to take if you’re going to cheat? Are you going to take 90% [probability] of being detected? Well, probably not. Are you prepared to run a 10% risk? Well, the difference is quite considerable... It’s almost an order of magnitude." He said any such assessment is complicated, and added that in his country, Sweden, for example, "I’m sure we cannot detonate a 10-ton explosion without detection."

Massimo Chiappini, research director of the Italian Institute of Geophysics, said on-site inspections will be crucial to follow-up quickly on ambiguous evidence from remote sensors. Before, during and after a nuclear test, he said, there is a complex skein of adjunct evidence that accumulates at the site. Inspectors might observe such clues as drilling equipment, diagnostic cables, possibly a magnetic field generated by the test and seismic aftershocks, in addition to radioactive particles and gases.

While the speakers cautioned that there is still much to be worked out in this politically contentious realm, further progress is expected with the United States rejoining the discussions after eight years.

The treaty’s premise is that weapons developers must test new designs to prove they work and that prohibiting such tests will curtail advances in weapons technology in existing nuclear states and proliferation of nuclear weapons to new states. As one questioner observed, however, some "new proliferators" are not necessarily trying to hide their activity and therefore might not be deterred by the threat that their tests could be exposed.

"Is the treaty verifiable?" Dahlman asked rhetorically. "That is a decision that has to be taken" at the national level "and based on each state’s security needs." He noted that 148 nations "have answered ‘yes,’ by signing and ratifying the treaty."

"We’re in a pretty different place, from a scientific perspective, from where we were 10 years ago," said Benn Tannenbaum, associate program director of the AAAS Center for Science, Technology and Security Policy. "The question that remains to be answered is a political one, and that is: Is that sufficient?"