175 5. DEEP ERT/IP for geothermal exploration and de-risking In statistical terms, the IAB currents transmitted during the three days of acquisition are on average of the order of 4.5 A, with minimum values of 3.2 A and peaks of 8.8 A, reached with transmissions in the South-East area on more conductive soils. The average Vmn potentials recorded are of the order of 3 mV, with average apparent resistivities around 20 Ω·m, with the lowest values, around 8–10 Ω·m, measured at depth (Figure 5.11). Figure 5.11 Pseudo-cloud of measured apparent resistivities (on the left) and histogram of measured apparent resistivities (on the right). The cloud of the measured apparent resistivities is displayed on Figure 5.11 (left). The total set of measurements consists of 7072 quadripoles (104 transmissions for 68 receiving dipoles). Before the resistivity measurements were processed from the global set, 147 measurements, equal to about 2%, were removed. Most of them had measured Vmn signal less than 0.01 mV. For the processing of the chargeability measurements, we opted for an arithmetic sampling of the discharge curve, using a delay time of 240 ms and 20 sampling windows of 80 ms. After resistivity inversion, we filtered the chargeability measurements, excluding data with a standard deviation above 10% and IP values outside the 0.01–30 mV/V range. This filtering removed approximately 2500 inaccurate measurements, representing about one-third of the dataset primarily associated with deeper quadripoles where the larger distance between receiver and transmitter resulted in lower potentials (below 0.5–1 mV). The inverted dataset showed average chargeability values around 5 mV/V. 5.3.6 Processing of resistivity and chargeability measurements The investigation enables us to reconstruct three-dimensional models of the distribution of resistivity and electrical chargeability of the subsoil, which highlight the main lithological characteristics of the site. The geological context is relatively
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