Geophysics and caving: An example from the apuan alps

Seismic techniques were used to locate an underground cave in the Apuan Alps, world-famous marble mountains within a regional natural park in Tuscany, central Italy. Cavers have recently discovered a very long as well as intricate passageway in the subsurface ending in huge and spectacular natural cavities. Since the initial part of the path involves climbing, crawling and an extensive knowledge of caving techniques, it is accessible only to well-trained and athletic cavers. In order to make it feasible for a larger audience, it would be helpful to find a way from the surface intersecting the tunnel not far from the big voids. Previous attempts of the speleologists to dig a passage where the cave is believed to be shallower along with GPR investigations were unsuccessful. We initially performed a seismic refraction survey to characterize the site in terms of seismic velocities and layer thicknesses. Subsequently, seismic events were generated with a hammer inside the cave. The signals were collected on the surface along two orthogonal spreads. A radio-triggering system was attempted. Localization of source points was affected by unfavorable propagation conditions and involved signal analysis in terms of arrival time, energy and waveform.