A global monitoring system which includes stations from the National Science Foundation (NSF)'s global seismic network is on a global "neighborhood watch."
The United States this week signed the Comprehensive Test Ban Treaty (CTBT), which will be verified through an International Monitoring System. This system consists in part of a primary and auxiliary seismic network, which will record evidence of any nuclear testing in violation of the treaty. The global network is being installed by the IRIS (Incorporated Research Institutions for Seismology) consortium and the U.S. Geological Survey, with support from the National Science Foundation.
Previous treaties have banned nuclear testing in all environments except underground, but the CTBT makes the ban complete by extending it to underground tests. The monitoring of underground tests has been the most controversial part of verifying the treaty.
The IRIS stations contribute not only to monitoring of the treaty, but also to the mitigation of earthquake hazards and scientific exploration of the Earth's interior. "The development of such multi-use seismic stations has created an opportunity for us to advance our fundamental understanding of earth's structure and dynamics while simultaneously contributing to this important societal need," says Robert Corell, assistant director of NSF for geosciences.
The treaty calls for a seismic network of 50 primary stations and 120 auxiliary stations that can detect seismic events of magnitude 4.25 and larger, and can locate those events with an uncertainty of less than 1,000 square kilometers. (A seismic event of magnitude 4.25 corresponds to an explosive yield of approximately one kiloton, the explosive equivalent of 1,000 tons of TNT.) The first early U.S. weapons were in the 15-20 kiloton range, as were the first tests of the Soviet Union, China, Britain, and India. France's first test was about 60 kilotons. The largest test has been about 50,000 kilotons, by the Soviet Union.
The official treaty monitoring system is in many cases only the "tip of the iceberg" in terms of facilities that have the potential to record seismic signals from a secret underground explosion, according to Greg van der Vink, director of planning at IRIS. "These scientific resources provide the technological equivalent of a global 'neighborhood watch' program that will greatly enhance treaty verification."
In central Asia, for example, the Kyrghyzstan and Kazakhstan regional IRIS network provides a detection threshold for an area of some 10 million square kilometers that averages about one seismic magnitude unit better than what is required of the treaty monitoring network. When translated to explosive yield, explains van der Vink, this magnitude difference corresponds to a potential detection threshold about 20 times better than that required of the monitoring network.
In the United States, networks installed for earthquake monitoring average two full magnitude units beyond treaty network requirements, and are thus able to detect explosions more than 200 times smaller than required by the monitoring system.
According to David Simpson, president of IRIS, "More than 50 of the stations that are part of the International Monitoring Network required by the treaty are IRIS stations that have already been installed as multi-use seismic stations." They fan across the globe, from Alaska to South America to Greenland to Europe, Africa, Asia, Australia, and Antarctica.