Resonant seismic wave interaction with acoustic cavities

"Resonance seismometry" will be a feature for the verification of the future Comprehensive Nuclear Test Ban Treaty (CTBT) during On-Site Inspections (OSI). To better understand the scientific underpinning of that field, we apply an analytical solution for plane elastic wave interaction with a spherical acoustic inclusion derived by Korneev (1996) using the model dimensions of an cavity created by an underground nuclear test. For a fluid-filled cavity small changes of the frequency can cause strong variations of the scattered field, and clear resonances potentially occur. For the OSI-application, the strongest peaks appear in an observable frequency range at around 15 Hz and 30 Hz. This would apply for the case that the cavity is filled by ground water after the explosion. We also investigate the case of a gas-filled acoustic cavity, and show that no resonances are observed. The spectral characteristics of the cavity scattering can be described by dominant S-wave scattering in a broad frequency range (0-95 Hz) and a monotonous increase of total scattered energy with frequency.