Advances in Three-Dimensional Modeling and High-Performance Computing to Improve Nuclear Explosion Phenomenology and Monitoring

Detailed modeling of the physical effects of nuclear explosions has been a subject of intense investigation at the U.S. national laboratories since their inception. Recent advances in numerical methods for wave propagation and the inexorable growth in computational power offer new opportunities to improve the fidelity of simulations of seismic wave phenomena for the purposes of improving physics-based understanding and monitoring of nuclear explosions. This presentation will summarize new modeling capabilities developed to improve understanding of the seismic waves emerging from an explosion. These capabilities allow representation of three-dimensional (3D) variations in physical properties of the earth and rely on the world- class computational resources available at LLNL. Specifically we are working in three thrust areas: 1) computation of regional distance intermediate-period (>5 seconds) synthetic seismograms in 3D earth models to assess the ability of these models to predict observed seismograms; 2) coupling of non-linear hydrodynamic simulations of explosion shock waves with an anelastic finite difference code for modeling the dependence of seismic wave observables on explosion emplacement conditions and near-source heterogeneity; and 3) simulation of surface topography in our anelastic finite difference code to include scattering and mode-conversion due to a non-planar free surface.