Policing the Peace

Abstract

S teven R. Bratt's belt started chirping as if on cue, precisely as he was boasting about a new global watchdog system for detecting nuclear tests. Bratt, a seismologist with the U.S. Department of Defense, retrieved the beeper from his hip and studied it for a few seconds. I've got an alert. It's from Lop Nor. Lop Nor is the Chinese test site, he explained. Two stations in a worldwide network of seismometers had just picked up vibrations emanating from central Asia, near China's known nuclear facility. The shock was small, about magnitude 3.5. In bomb equivalents, it would correspond to less than a half kiloton explosion. In this case, however, Bratt suspected the alert was just a minor earthquake. Timing provided an important clue: The shock had originated at 12:19 Greenwich Mean Time, which is not the kind of round, on-the-hour time that countries usually choose for performing a major weapon test. Seismic analysts would later confirm Bratt's hunch when they determined that the Chinese vibrations actually originated at an unlikely place to stage a test, hundreds of kilometers away from the Lop Nor site. The impromptu demonstration nonetheless made a good advertisement for the new international monitoring system-an ever-vigilant network of sensors strung around the globe, listening, sniffing, and waiting. The system, which currently includes 140 stations, is a prototype of the one required by the Comprehensive Test Ban Treaty (CTBT), currently being negotiated in Geneva. After nearly 40 years of discussion, the world is moving toward adopting the treaty-if all goes well-as early as this summer, thereby prohibiting all nuclear testing. To back up a ban on nuclear testing, the treaty calls for a four-part monitoring system consisting of seismic, hydroacoustic, infrasound, and atmospheric radionuclide sensors. According to sections of the treaty already written, all the data collected by this system will flow into an information hub called the International Data Center, a prototype of which is located in Arlington, Va. Bratt is the Defense Department's program director overseeing development of the data center. Each element of the monitoring arsenal will patrol a different region of the planet, though they overlap to some degree. The seismic network, the backbone of the system, will draw on 50 primary and 120 auxiliary stations to pick up vibrations from any underground tests. The hydroacoustic system will keep watch for ocean blasts using six underwater sound receivers tied in with five islandbased seismometers. An infrasound network of 60 microbarographic pressure sensors will listen for atmospheric explosions. Lastly, 75 radionuclide stations will monitor the winds for the distinctive isotopic aroma vented into the atmosphere by atomic blasts.