IRIS Concludes Nuclear Test Study for US Congress


Since 1993 the Department of Energy has been disclosing information on more that 200 formerly unannounced nuclear tests performed at the Nevada Test Site. After the initial disclosure of information, the US Congress Office of Technology Assessment (OTA) requested IRIS to analyze "which of the formerly unannounced tests had previously been identified... on the basis of publicly available seismic data... ." In the letter to IRIS's Director of Planning, Gregory van der Vink, OTA stated that "This announcement provides a good opportunity to test the power of open-source seismic monitoring to detect unannounced nuclear weapon tests."

Several IRIS member institutions, including: the Lamont-Doherty Earth Observatory, the California Institute of Technology, the University of Nevada, and the Russian Academy of Sciences as well as the USGS were involved in this cooperative effort. Through an assessment of data from five regional and teleseismic networks, the study demonstrated that 85% of all unannounced tests were independently detected and listed in open seismological bulletins. At regional distances, tests with magnitudes as small as 1.4 were detected. At teleseismic distances, stations in the former Soviet Union detected all US unannounced tests with magnitudes of 4 or larger. Since 1983, only two tests were seismically undetected - tests that presumably had less than one ton of TNT equivalent yield. The conclusions of the study were published in the American Geophysical Union's EOS on July 30, 1996.

[Graph]

Prior to the DOE's announcement, 73% (149 of 204) of previously unannounced US nuclear tests were detected and are listed in open seismological bulletins. The detection rate was 89% (16 of 18) for tests conducted since 1983. After the DOE announcement, a review of the regional seismic records increased the number of detections since 1963 to 85% (173 of 204).


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