The use of electrical resistivity tomographies in active tectonics: examples from the Tyrnavos Basin, Greece

A 2D Electrical Resistivity Tomography (ERT) survey was carried out in the tectonically active Tyrnavos Basin, Eastern Thessaly, Greece. The principal aims of this research are to test the efficiency of this relatively new geoelectrical technique when applied to the recognition and the geometrical characterisation of active faults and to improve our tectonic knowledge of the investigated area. We therefore carried out several tests performing the geophysical prospecting across morphotectonic scarps or fault traces along which the Late Quaternary tectonic activity is well documented by previous structural, stratigraphic, morphotectonic and palaeoseismological researches. The tests concerned the electrode spacing, the maximum depth of investigation, the quality-to-costs ratio, etc. In a second phase of the survey, we applied this geophysical methodology to specific sites along the major tectonic structures bordering the Tyrnavos Basin, in order to obtain, firstly, a better tectonic knowledge of the area, secondly, to solve particular and local geological problems and, thirdly, to help deciding between ambiguities left unsolved by superficial surveys. Accordingly, numerous ERT with different electrode spacing (from 2 up to 50 m) and depth of investigation (from 0.5 to 120 m) were performed with a dipole-dipole array using a multielectrode system, with 32 electrodes equally spaced along a straight line, for data acquisition. Combining advanced technologies for data acquisition and new tomographic techniques for resistivity data inversion, we obtain a large data-set of high-resolution electrical images of the subsurface across active faults. General and particular results concerning the application of ERT techniques for mapping subsurface active faults are discussed, while advantages and limits in applying this geophysical methodology are emphasised.