Seismic wave propagation through a low-velocity nuclear rubble zone

摘要

A 2-dimensional finite-difference code has been developed as part of the Hydroacoustic Nuclear Proliferation Monitoring Project (ST639). This code is used to model seismic and acoustic wave propagation in the Earth's crust and oceanic water column. As a demonstration, we investigate the propagation of seismic energy through a low-velocity region corresponding to the rubble zone created by an underground nuclear explosion. The geometry of the simulated source and surface recording instruments is representative of a seismic refraction survey. The purpose of this numerical simulation is to determine perturbations in the seismic wave field due to the low velocity region (nuclear cavity) can be detected at the surface. Wave energy passing through the cavity is noticeably delayed, and is easily observed on cross-sections of the P and S wave fields. Synthetic seismograms recorded at the surface demonstrate an amplitude reduction and phase shift for those stations corresponding to ray-paths through the cavity. A significant fraction of energy is reflected off the low-velocity zone, and propagates as backward traveling waves.