Dispersion diagram analysis for underground cavitie : A finite difference approach

Identifiing physical phenomena induced by underground cavities on seismic surface waves will improve void detection methods involving surface seismic waves. Recent works (Leparoux et al., 2000) based on numerical analysis in elastic media with 2nd order finite differences method (Virieux, 1986) and experimental validation show the capability of Rayleigh waves to detect underground cavities, as well as other works (Shtivelman (2000)). Nevertheless, these results show the necessity of accurate numerical modelling taking into account weathered structures and different shapes of cavity. A new finite difference spatial stencil has been proposed by Saenger et al. (2000) for reducing numerical dispersion. After describing this numerical method applied to surface waves analysis, we present seismograms and dispersion diagrams for different cavity typlogies and shot gathers.