Improving Ground Motion Simulation Capabilities for Underground Explosion Monitoring: Coupling Hydrodynamic-to-Seismic Solvers and Studies of Emplacement Conditions.

摘要

This project involves research being performed to improve ground motion simulation capabilities for underground explosion monitoring. We are working along two thrusts: (1) we are coupling hydrodynamic (non-linear shock) and seismic (linear anelastic) wave propagation codes; and (2) we are investigating the effect of source emplacement conditions on ground motions. For both thrusts we are modeling explosion motions using GEODYN, an Eulerian hydrodynamic code developed at Lawrence Livermore National Laboratory (LLNL). This code includes many important features for modeling shock waves in geologic materials, including non-linear response (e.g., effects of porosity, tensile failure, yielding) and adaptive mesh refinement. However, numerical solution of the hydrodynamic response is computationally expensive due to non-linear constitutive behavior, especially when compared to elastic wave propagation solvers. To propagate ground motions from the non-linear explosive source region to far-field seismic stations we are using a one-way coupling strategy to pass motions from GEODYN to WPP (LLNL's anelastic finite difference code for seismic wave modeling). Motions computed by GEODYN and recorded on a dense grid span the ranges where motions become linear (elastic). These are saved, processed and passed to WPP where they are introduced as a boundary source and continue to propagate as elastic waves at lower numerical cost than with GEODYN. In the past year we have worked on several important details to gain confidence that coupled GEODYN-to-WPP simulations are accurate. This involved modifying GEODYN to accurately model elastic surface waves. This is challenging because GEODYN uses hydrodynamic rather than elastodynamic equations of motions for the continuum.