GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.3 GNGTS 2024 Full-decay spectral modelling of tme-domain induced polarizaton decoupling model and forward meshes with EEMverter A.Bollino 1 , G. Fiandaca 1 1 The EEM Team for Hydro & eXploraton, Department of Earth Sciences “Ardito Desio”, Università degli Studi di Milano, Milano (Italy) Direct current (DC) resistvity and induced polarizaton (IP) geophysical methods are widely used in geophysical near-surface investgatons, gaining informaton about subsurface conductvity structures by injectng electric currents into the ground and measuring electric voltages at diferent locatons. The DC resistvity method provides informaton about the electrical conductve propertes of the subsurface. In contrast, the IP method targets the capacitve characteristcs ofering additonal insight into the physical and electrochemical nature of subsurface materials. The IP phenomenon has been widely investgated both in tme (TDIP) and frequency (FDIP) domains, in the laboratory, or through feld studies. The TDIP has been used for many years for disseminated ores and mineral discriminaton (e.g. Vanhala and Peltoniemi, 1992; Seigel et al., 1997, 2007). Over the last 20 years signifcant advancements in IP research have taken place, partcularly with respect to the spectral content of the IP signal, which can be applied to engineering and environmental problems, such as the detecton of contaminants and old landflls (e.g. Weller et al. 1999; Gazoty et al . 2012; Fiandaca et al., 2015; Johansson et al . 2015), and the derivaton of grain size distributon parameters in unconsolidated sediments (e.g. Vanhala et al., 1992, Kemna et al., 2004, 2012). In the frequency domain, IP phenomena can be represented as a complex conductvity (ω) that varies with frequency (ω), which can be expressed as: (ω)= ( ) (1) where * denotes a complex term, is the magnitude of conductvity, is the phase angle between injected current and measured voltage, is the real component of conductvity, ( ) is the imaginary component of conductvity, is the angular frequency representaton of frequency , and (Binley, 2015). By neglectng electromagnetc (EM) efects, the complex potental is linked to the complex conductvity through Poisson’s equaton: (2) σ* σ* | σ ( ω ) | e iφ ( ω ) = σ ′  ( ω ) + iσ ′  ′  ω | σ ( ω ) | φ σ ′  ( ω ) σ ′  ′  ω ω = 2 π f f i = −1 u* ( ω ) = u ′  ( ω ) + iu ′  ′  ( ω ) ∇ ⋅ j* S ( ω , r ) = ∇ ⋅ [ σ* ( ω , r ) E* ( ω , r ) ]