Analysis of Near-Field Seismic Waveforms from Underground Nuclear Explosions

The first part compares the Mueller Murphy and Helmberger Hadley source representations and investigate whether there are any features of the near-field observations which tend to favor one over the other. The scaling relations in the two formalisms are such that the spectra are virtually indistinguishable between 2 and 5 Hz. Although the Mueller Murphy source is too rich in high frequency energy, a moderately low Q value for the near-field crust can make it agree with the observations. In the second part, the vertical particle velocity records for three nuclear explosions (DISCUS THROWER, MUDPACK and MERLIN) detonated in dry tuff of alluvium were modeled using generalized ray theory to determine the effective source functions. It was found that simple ray theory can be used to consistently predict the amplitude of the initial P wave for ranges greater than one depth of burial. At closer ranges the amplitudes are systematically overpredicted. Using the announced yields of the events, a scaling law was determined for source strength of nuclear explosions detonated in dry tuff or alluvium, and was used to predict the amplitudes from several other Yucca Flats events. The third part, introduces a method for the simultaneous inversion of near-field waveforms for source and structure parameters. The source may be parameterized by any of several effective source functions.