Electrical Resistivity Tomography (ERT) is a geophysical technique that allows to estimate the different resistivity values ​​of the materials present in the subsoil. It is based on the injection of electric current into the subsoil with a pair of electrodes and the subsequent measurement of the electric potential using another pair of electrodes. it allows to investigate areas at greater depth compared to GPR . The result of an ERT acquisition is an image that represents the distribution of resistivity values ​​at different depths of the subsoil in false colors. The different resistivity reveals differences in the underground stratigraphy allowing to investigate the subsoil in a non-destructive way.

How does it work?


Four geoelectric surveys were carried out as part of the VESTA project: in the area behind the ancient baths; in the residential areas developing west of the monumental Temples of Neptune and Hera; between the Temples of Neptune and Hera.
The investigations aimed to analyze the variability of the electrical conductivity (or resistivity) of the subsoil with different levels of depth of investigation.
Electrodes A and B were positioned in the investigated areas from which the electric current is sent. The current generates an electrical voltage which is sensed by two other electrodes, M and N.


The survey data are processed to obtain a map of the soil resistivity which is interpreted by the experts. It is possible to analyze the stratigraphy of the subsoil by identifying the various geological or man-made formations this way. The image shows the map of the area between the Temple of Neptune and the Temple of Hera.

How do we read a resistivity map?

Let’s look at the results of the investigations carried out in the area of ​​the baths and imagine exploring the subsoil at various depth levels (indicated on the left of the legend). The areas with greater resistivity have colors tending to fuchsia and indicate the presence of travertine, a sedimentary rock. The areas with a color tending to blue have a lower resistivity and instead indicate the presence of alluvial deposits.