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Broadband, vertical component seismogram recorded at the IRIS Global Seismographic Network station Nilore (NIL) in Pakistan. The signal is from the magnitude 5.2 Indian nuclear test on May 11, 1998. Although this station is not part of the official International Monitoring System for the Comprehensive Test Ban Treaty, it is the closest open seismic station to the Indian test site 750 km to the south.

According to Indian announcements, the test consisted of a 43-kiloton thermonuclear explosion, a 12-kiloton fission explosion and a 0.2-kiloton fission explosion. Reportedly, the nuclear devices were detonated simultaneously in two deep holes, drilled roughly 1,100 yards apart.

In addition to confirming that a nuclear explosion had occurred at the Indian test site, the seismic data has allowed independent evaluation of the validity of India's claims. In contrast to India's announcement of a cumulative yield of 55 kilotons, a magnitude 5.2 seismic event at the Indian test site corresponds to an underground nuclear explosion with an equivalent yield of approximately 5-25 kilotons.

For further discussion see:

"False Accusations, Undetected Tests and Implications for the CTB Treaty" by Gregory van der Vink, Jeffrey Park, Richard Allen, Terry Wallace and Christel Hennet, Arms Control Today, May 1998, p.7-13.

"The May 1998 India and Pakistan Nuclear Tests" by Terry C. Wallace, Seismological Research Letters, September/October 1998, p.386-393.

"Monitoring Nuclear Tests" by Brian Barker, Michael Clark, Peter Davis, Mark Fisk, Michael Hedlin, Hans Israelsson, Vitaly Khalturin, Won-Young Kim, Keith McLaughlin, Charles Meade, John Murphy, Robert North, John Orcutt, Chris Powell, Paul G. Richards, Richard Stead, Jeffrey Stevens, Frank Vernon, Terry Wallace, Science, 25 September 1998, p.1967-8.

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