Simulation Analysis of Low Frequency Ground Motions Observed from Selected Atmospheric Nuclear Explosions at the Nevada Test Site

摘要

This report describes the results of a continuing investigation of the characteristics of the low frequency ground motions produced by atmospheric explosions. The studies reported here have focused on two aspects of this problem: (1) the full-scale validation of nuclear tests, and (2) the preliminary evaluation of a theoretically-based prediction methodology. With regard to the validation study, the mathematical model has been applied to the theoretical simulation of ground motion data recorded from the Nevada Test Site atmospheric nuclear explosions TUMBLER I, UPSHOT-KNOTHOLE 10 and SMALL BOY. The results of these simulations have confirmed the fact that the observed low frequency ground motions from such explosions can be accounted for by the airblast-induced, elastic surface waves. Moreover, the simulation analysis of the ground motion data recorded from the near-surface SMALL BOY explosion has confirmed the existence of an 'exclusion radius' for such events, within which incident airblast energy is not efficiently coupled into the surface wave mode of propagation due to dissipation associated with strong, nonlinear interaction effects. On the other hand, the evidence provided by the TUMBLER I and UPSHOT-KNOTHOLE 10 analyses has indicated that this exclusion radius is effectively zero for explosions with significant height of burst.