Analysis of Shear Wave Generation by Decoupled and Partially Coupled Explosions
Final rept. 25 Jan 2006-30 Jul 2009
SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA
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We compare near field and local seismograms from partially and fully decoupled chemical and nuclear explosions, and water-filled cavity nuclear explosions, with seismograms from tamped explosions in the same source location, and compare records of a centered and an offset explosion in a spherical cavity, all to identify and characterize shear waves generated by decoupled explosions. We numerically model the shear wave generation due to hydrofracturing, opening of pre-existing cracks, asymmetric nonlinear deformation outside the cavity due to only partial decoupling, offset of the source within the cavity, ellipticity of the cavity, and a flat-floored cavity due to recrystalization of melted salt, and compare the simulations with observations. We also model an offset source analytically to investigate the effect of longer lasting reverberations. The observations and modeling indicate that partially and fully decoupled explosions generate significant shear wave energy at the source through various source asymmetries, including offset of the source and aspherical cavity shape.