PARAMETRIC STUDIES OF NEAR-SURFACE EXPLOSIONS

We have performed quasi-3D high-resolution numerical simulations of surface and underground explosions using LLNL’s massively parallel eulerian hydrocode GEODYN to assess the impact of parameters such as yield, height of burst (HOB), depth of burst (DOB) and geological material on the resulting overpressure in air and seismic motions at distance. The material properties span a large spectrum from hard rock, such as granite with low porosity, to weak material, such as dry alluvium. Arrival times to surface station are determined by the shock wave propagation and the coupling of ground motion. We show that overpressures and peak velocities due to the same yield at the same scaled HOB/DOB are functionally very similar regardless the geological fabric and therefore the response can be scaled. Moreover, the impulse is calculated by integrating the initial positive pressure time-history. It was found that the functional form of the impulse as a function of scaled HOB/DOB is also consistent for emplacements above ground, at ground level and down to depths where cratering occurs regardless for all geological materials even though the material properties show drastic geomechanical variations. While the current study used numerical simulation from idealized blast and settings, additional factors can complicate observed seismic signals and bias the amplitudes and subsequent yield and HOB/DOB estimates. For example, we show that the emplacement lithology strongly impact seismic amplitudes for deeply buried explosions. Furthermore, the behavior with HOB/DOB is different for the materials considered. Results are compared with limited experimental data.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.