BOX 4.2 Nuclear Monitoring
Since the first underground nuclear tests in the late 1950s, underground test monitoring and test ban treaty verification have motivated the development of better seismic networks (see Section 2.3). With the breakup of the former Soviet Union and the increased number of emerging nuclear nations, the emphasis has shifted from a bilateral superpower test ban treaty to a global comprehensive test ban treaty (CTBT) and the Nuclear Nonproliferation Treaty. In the current plans, seismic networks represent one of four main technologies for monitoring the CTBT (along with infrasonic, hydroacoustic, and radionuclide techniques). The seismic component of the IMS will utilize 170 stations and reduce the global detection threshold to around mb4.0. The primary stations (alpha stations) are mostly dense arrays of high-quality, short-period sensors, located at carefully selected sites around the globe, with equipment for continuous telemetry to the International Data Center (IDC) for the primary purpose of detecting seismic events on a global scale. Auxiliary stations (beta stations) are meant to support rapid, on-demand, automatic retrieval of data for use in improving the location of events detected by the primary network. Most of the beta stations will be drawn from established three-component, broadband stations of the FDSN, ensuring a strong partnership between the CTBT monitoring community and earthquake scientists. Approximately 1000 separate channels of seismic data will be transmitted via satellite in real time to the IDC in Vienna, Austria, where they will be analyzed automatically to determine routine source parameters such as location, depth, origin time, and magnitude. Although the ultimate capabilities of the monitoring system will not be known until the network is fully deployed and operational, the experience with recent nuclear tests in India and Pakistan suggests that the IDC and IMS will provide an unprecedented system for real-time global seismic monitoring with low detection thresholds.1
Monitoring CTBT compliance will be more challenging than past arms control treaties, because it will require high-confidence identification of any nuclear explosion, however small, carried out in remote regions of the world. The CTBT has motivated a broad program of research, focused on regional monitoring of small seismic events.2 The results of this research are needed for two treaty monitoring goals. First, there is a need to locate all of the detected seismic events within 1000 square kilometers, because this is the largest region that can be inspected to assess a possible treaty violation. Achieving this goal will require detailed seismic calibration information (travel times, phase arrivals) for each of the IMS stations. Second, algorithms must screen out the large number of natural events that will be detected, based on location, depth, and other source characteristics. To advance these capabilities, the Department of Defense (DOD) currently supports one of the largest basic research programs in seismology in the federal government ($12 million in FY 2000). To increase the involvement of earthquake researchers, DOD plans to make all of the IMS data available for open research and hazard monitoring operations.