GNGTS 2015 - Atti del 34° Convegno Nazionale

148 GNGTS 2015 S essione 3.3 gained widespread interest also in TDEM, FDEM and LOTEM prospecting, as documented in many papers, recently appeared (e.g., Chang-Chun and Bin, 1994; Hoheisal et al. , 2004; Zaslavsky et al. , 2011; Marchant et al. , 2014). In the present MT simulations, the 3D body is a dispersive conductive prism immersed in a non-dispersive resistive half-space. This resistivity contrast is motivated by previous simulations on 1D and 2D models. Dispersive conductive layers sandwiched between dispersion-free resistive layers (1D), and dispersive conductive, infinitely long prisms hosted in a dispersion-free resistive half-space (2D) have shown the most remarkable distortions (Mauriello et al. , 1996; Esposito and Patella, 2009). Moreover, such a model, by a proper choice of the prism’s size and depth, can be useful to interpret MT data in the prospection for oil and geothermal reservoirs (Pellerin et al. , 1996; Zhdanov and Keller, 1994). A MT field dataset, related to a geothermal exploration program in the eastern Snake River Plain, Idaho, (Stanley, 1982), is re-analyzed within a 3D framework, in order to highlight the greater interpretative potential that rises from the inclusion of 3D dispersion effects in MT data analysis. 3D simulation of dispersive effects inMT. Fig. 1 shows the 3Dmodel assumed for studying the IP effects in MT and the responses generated by the body. A horizontal dispersive prism with resistivity ρ 0 =10 Ωm is buried in a non-dispersive half-space with resistivity 200 Ωm. The Fig. 1 – At the top the 3D mode and the selected profiles with corresponding station sites on the left, on the right the model seen from above. At the bottom modulus (top diagrams, in Ω m) and phase (bottom diagrams, in deg.) of the two orthogonal TM and TE modes of the MT apparent impedivity response against distance (in m) along the profile. The blue curves refer to the reference not dispersive response, while the red curves to the dispersive case.