A Comparison of the Spectral Characteristics of Nuclear Explosions Detonated Below and above the Water Table
Rept. for Mar 1988-Feb 1989
TELEDYNE GEOTECH ALEXANDRIA VA ALEXANDRIA LABS
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A comparison of the spectra of nuclear shots detonated below and above the water table WT is made by analysis of mostly the regional phase Pn recorded at two common stations. Parameters derived from each record include estimates of corner frequency F sub c and the low-frequency spectral level A sub 0, after the spectra have been corrected for the effects of spatial attenuation. The time-domain measurements of AT, a measure of m sub b, are also made on each observed record. Results from 22 Nevada Test Site NTS shots recorded at the DWWSSN digital station, JAS, indicate that plots of f sub c versus A sub 0 show some separation between the below and above WT populations whereas plots of f sub c versus AT show no significant separation. For a fixed yield, f sub c for shots below and above WT are nearly indistinguishable whereas both A sub 0 and AT are considerably larger for shots below WT than for those above WT, presumably due to improved source coupling of shots in water saturated environment. A comparison of yields estimated from A sub 0, AT, A sub 0 combined with f sub c, and AT combined with f sub c demonstrates that substantially more precise yield determinations can be made if it is known whether the shot was detonated above or below WT. Results from the analysis of 17 NTS shots recorded at the RSTN station, RSSD are generally not as well defined but appear similar to those from the JAS recordings. The largest difference between the below and above WT shots of a given yield lies in their low-frequency spectral level and, to a slightly smaller extent, in their M sub b values.
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