Contribution to the Understanding of Specific Signatures in the Interaction of Surface Waves with Underground Voids

Abstract

Shallow cavities, such as karstic caves in carbonate bedrock and near-surface underground mine workings or tunnels, constitute serious hazards for people and existing constructions due to the risk of collapse and subsidence. This phenomenon is growing fast with climate change causing damage to buildings and increased urban development costs. Karstic features, voids, surficial dissolution, fissuring, alteration and unconsolidated material are thus major challenges for geophysical methods that could play a major role in detection. Recent investigations have reported good results for cavity imaging using surface wave seismic methods. However, despite successful case histories, business as usual void detection is still challenging due to the complexity of near surface materials and probably a lack of understanding regarding the interaction of surface waves with voids. Recent data acquired in the context of a search for underground unpaved cavities provide new insights into the use of surface waves for the detection of these objects. Considering the findings, it appears that surface waves penetrating above and below the void may still propagate horizontally without clear features of altered propagation characteristics with respect to different actions, variations in dispersion, or both, which encourages rethinking of the systematic nature of diffraction research in operational applications.