The Contribution of Two-Dimensional Source Effects to the Far-Field Seismic Signatures of Underground Nuclear Explosions

Two-dimensional calculations of underground explosions are able to include free surface interaction effects and the depth dependence of overburden pressure and material properties, as well as the complex constitutive models for geologic materials developed in one-dimensional (spherically symmetric) studies. Eleven axisymmetric calculations of explosions in granite are analyzed in this study to determine the two-dimensional effects on the far-field body and surface waves and the magnitude mb and Ms. Seven of these are hypothetical 150 KT explosions at depths from 159 to 1000 meters calculated by Applied Theory, Inc. (ATI). These show depth effects that are different, though not strikingly so, from those calculated with one-dimensional source models. The other four calculations were done by Systems, Science and Software (S-Cubed). The first was for a specific event (PILEDRIVER), and the depth and yield were varied for the other three. the near- and far-field data for PILEDRIVER were matched rather well, except that the spallation was too large in the calculation. Sponsored in part by DARPA.