The impact of multiple transmitters on signal strength in Deep Electrical Resistivity Tomography data: an experiment in the Vajont valley (north-eastern Italy)

Electrical Resistivity Tomography method has boosted its potentials since the development of new-concept resistivity-meters. Key improvements include a much better data quality and the reduced logistics required to operate long spreads in rough terrains. The Multi-Source (MS) resistivity-meter incorporates both these two features and, moreover, its peculiarity of transmitting and receiving with short isolated wires reduces inductive and capacitive coupling in cables and multiplexer. It is a modular system based on stand-alone units remotely controlled via radio signals. Modularity eases the use of the system but the real innovative and most important feature is its capability of injecting current simultaneously with different dipoles. The system was tested in the Vajont valley, in north-eastern Italy, with the purpose of imaging the deep sliding surface of the catastrophic landslide occurred in 1963. An array of potential loggers was laid down parallel to the MS line in order to gain full control on transmitted/received signal character and strength and finally validate the system reliability. The MS waveform was clearly recognisable up to a distance of more than 1 km in single transmitter mode, while using multiple transmitters the threshold distance is probably far beyond and it was not reached. A potential of 0.02 mV was identified as the detection threshold. A one-to-one correspondence was observed, also at maximum offset, between MS measurements and potential values recorded with the data loggers indicating the effectiveness of the tested system in removing self-potentials.