Basic Research in Nuclear Test Monitoring: Explosions in Non-Spherical Cavities:Investigations of Enhanced Backscattering

摘要

We report on two studies. The first is a theoretical study of the seismicradiation from explosions detonated in finite cylindrical tunnels embedded in a homogeneous, isotropic, elastic medium. We developed a frequency domain boundary element/discrete wavenumber algorithm to model the seismic wavefields from such sources, and applied the algorithm to study two specific cases of explosion sources-nuclear and non-nuclear. Our calculations show different source radiation patterns between the two types of explosions, especially when the explosion is located off-center in the tunnel in which case the non-nuclear explosion radiation displays strong directivity effects. Both types of explosions radiate significant shear wave energy outside the cavity. The second study is on enhanced seismic backscattering from rough interfaces. We experimentally and numerically investigate the scattering of an acoustic P wave incident on a highly irregular, random acoustic-elastic interface to determine whether enhanced backscattering occurs. The experiments involve ultrasonic waves reflected from a glass surface etched to produce a highly irregular 3-D surface. We find that 2-D numerical results predict the 3-D experimental results well at small incident angles. Both numerical and experimental results strongly support the presence of enhanced backscattering. Explosion seismology, Non-spherical cavities, Seismic scattering, Enhanced backscattering.