Source Time Functions and Spectra for Underground Nuclear Explosions

The model of Haskell for explosion source time functions and spectra fails to satisfy data in the short-period band recorded teleseismically from the three Amchitka Island underground nuclear tests: LONG-SHOT, MILROW, and CANNIKIN. A more recent model due to Mueller and Murphy satisfies the data quite well. The difference in the two models is basically in the fall-off at high frequencies. A simple revision of Haskell's model produces waveforms and spectra nearly identical to ones from Mueller and Murphy's model. This revision requires velocity waveforms to have a rise time of extremely short duration at the elastic boundary, a premise validated by actual near-field measurements. Waveforms are derived from the revised Haskell model and the Mueller and Murphy model and illustrated for pressure at the elastic boundary, reduced displacement potential at the elastic boundary, and far-field displacement. Corresponding spectra are derived and illustrated.