Symposium Abstract: VLF Radio for underground communications, 1992, Gibson A. D.

SHALLOW KARST EXPLORATION USING MT-VLF AND DC RESISTIVITY METHODS, 1995, Guerin R. , Benderitter Y. ,

A geophysical test was carried out over a well-located and fairly embedded karstic conduit. The MT-VLF method was selected because of its high resolution and its ability to provide a resistivity parameter sensitive to water and clay. This method was used together with DC resistivity methods which allow vertical adjustment of the VLF data and show consistency between the investigation and target depths. After correcting the deformations due to the polarization of the primary field, the MT-VLF data show clearly, in the central part of the site, that the conduit does not coincide with an anomaly axis but coincides with the boundary between a conductive area and a resistive area. 2D modelling confirms that direct detection of the conduit is not feasible and that the conduit is located close to a conductive zone corresponding to a completely clay-filled fractured zone. This situation was observed on the whole site and the conduit seemed systematically to thread its way between the conductive zones to join the outlet. The distribution of the conductive fractured zones and the direction of the hydraulic gradient were two important elements in predicting the location of the conduits. A 3D approach would increase the probability of finding the conduits in such a case

Extremely Low Frequency Radio Emissions in Bat Caves, 1996, Koemel, Walton C.

Bats produce very low frequency (VLF) radio pulses and display magnetic qualities. Extremely low frequency (ELF) radio emissions were observed inside bat caves. Ground return currents from 60 Hz AC power systems run through the ceiling of some bat caves.

Cave Archaeology of Belize, 1996, Mcnatt, L.

Bats produce very low frequency (VLF) radio pulses and display magnetic qualities. Extremely low frequency

Modelling of karst structures by geophysical methods. An example: the doline of S Pietro dei Monti (Western Liguria), 1998, Armadillo E, Massa F, Caneva G, Gambetta M, Bozzo E,

Integrated geophysical investigations of karat structures were carried out in Liguria and Piedmont (NW Italy); this paper refers to the S. Pietro dei Monti doline, in the karat area of Mt. Carmo (Savona). The techniques used in the integrated study were magnetics, electromagnetics and seismic refraction. The target was to identify, without drilling, the nature of the doline, for example if it is of dissolution or collapse type. A preliminary susceptibility sampling of the outcrop and topsoil and the diffuse fractures with a probable water seepage suggested magnetics and VLF electromagnetics. Such methods applied in an area with an extremely low cultural noise allowed modelling of the buried structure of the doline

Improved karst exploration by VLF-EM-gradient survey: comparison with other geophysical methods, 2005, Bosch Fp, Muller I,

The knowledge of size, density and both orientation and vertical distribution of fractures as well as their opening and filling material or overburden thickness is a valuable contribution to estimating hydraulic conductivity and to evaluating the vulnerability and protection strategy of karst aquifers. To obtain some of these parameters and to ascertain high-permeability zones, the Very Low Frequency-Electromagnetic Gradient (VLF-EM GRAD) method was applied, together with Radio Frequency-Electromagnetics (RF-EM), Radioinagnetotellurics (RMT), Geoelectrical Tomography and refraction seismics, over a karstic terrain in the Swiss Jura Mountains. In this area, karst springs infiltrate a porous aquifer. This survey investigated the highly permeable karst structures, which provide fast water-infiltration pathways into the karstic flow network. A dye tracer test validated the geophysical results. The results show the efficiency and reliability particularly of the VLF-EM GRAD method, for high-resolution investigation at shallow depths and for its potential for fast data acquisition over large surfaces at catchment area scale without ground contact