Inversion of IP-affected electrical-source transient electromagnetic data observed in the groundwater survey from eastern Tibet, China

Recent advancements in the signal-to-noise ratio of transient electromagnetic (TEM) devices have highlighted the significance of induced polarization (IP) effects in areas containing polarizable materials such as clays or sulfide minerals. These effects are characterized by an abnormally rapid decay followed by late-time negative values in the voltage response, which often lead to unsatisfactory outcomes in conventional resistivity-only inversion workflows. Previous research demonstrated that incorporating the Cole-Cole complex resistivity model into an inversion workflow enhances the characterization of this phenomenon. In a recent hydrological survey in eastern Tibet, China, significant TEM-IP-affected phenomena were observed during the implementation of an electrical-source TEM system to map the distribution of groundwater. In this instance, data from two representative survey lines were inverted using a modified quasi-two-dimensional (2D) regularized Newton inversion scheme, which simultaneously extracted the DC resistivity and three IP parameters: chargeability, time constant, and frequency dependence. The results revealed clear conductive polarization distributions against the resistive host, correlating well with groundwater-enriched weathered layers, as confirmed by borehole lithological logs. Consequently, conductive polarization signatures were identified as potential key indicators of groundwater presence considering potential associations with clay and shale. This case study emphasizes the significance of accounting for potential IP effects in TEM surveys and highlights the advantages of multiparametric inversion for achieving more accurate results and enhancing the interpretation of subsurface properties.