Determining geophysical properties of a near-surface cave through integrated microgravity vertical gradient and electrical resistivity tomography measurements

Vertical-gradient microgravity and electrical-resistivity tomography geophysical surveys were performed over a shallow cave in the Italian Armetta Mountain karst area, close to the Liguria-Piedmont watershed. The aim of this study was to test the geophysical response of a known shallow cave. The shallowest portion of the cave exhibits narrow passages and, at about 30 meters below the entrance, a fossil meander linking two large chambers, the target of the geophysical survey. The integrated results of the two surveys show a clear geophysical response to the cave. The surveys exhibited high resistivity values and a negative gravity anomaly over the large cave passages. This work confirms the ability of these geophysical techniques to give the precise location of the voids, even in complex environments. The application of these techniques can be successful for site surveying where the presence of hollows may be expected.