http://userpage.fu-berlin.de/geodyn/tut ... aeoSci.pdfsays
There are a number of geophysical techniques that can be used to detect the presence of caves and other voids below the surface. Microgravity is popular and effective since there is clearly a large difference in density between the surrounding substrate and the void (Butler, 1984; Smith & Smith, 1987; Linford, 1998). However, gravity methods have the limitation that they do not detect the actual shape of the void but rather require the surveyor to postulate a possible shape, run a simulation, and see whether the simulated outcome matches the observed data. With a priori knowledge of likely shape (when verifying documen- tary evidence of a mine or tunnel, for example) this can be very effective, but when prospecting for an unknown cavern it is a major disadvantage. Resistivity tomography can also be used since the resistance of the void will be higher than the surrounding substrate (Noel & Xu, 1992; Manzanilla et al., 1994). Unfortunately, limestone it- self has a very high resistance which means that this technique is less likely to be successful. A third tech- nique is geophysical diffraction tomography using low- frequency sound waves, an approach which has been used with some success (Levy et al., 1996). The main disadvantage with this technique is that the placing of the geo- and hydrophones required can be difficult and time consuming which makes it less appropri- ate for prospecting.
Also,
https://gsa.confex.com/gsa/2011AM/final ... 192658.htm