Anomalous Rapid Voltage Decay in Transient Electromagnetic Data Caused by IP Effect: A Synthetic Study

Summary The induced polarization (IP) effects, associated with polarizable bodies, are increasingly observed in the transient electromagnetic (TEM) surveys, often characterized by rapid voltage decay followed by sign reversal. In a field TEM survey over a Volcanogenic Massive Sulfide (VMS) deposit, which exhibits high IP properties, an anomalous voltage decay without sign reversal was observed. To enhance data interpretation, we developed a 1D model using Cole-Cole parameters derived from spectral induced polarization (SIP) measurements of borehole core samples from the VMS area. The synthetic data exhibit rapid decay without sign reversals, consistent with the field observations. By performing both resistivity-only (RO) and IP-incorporated inversions, the results demonstrate that only the IP-incorporated inversion accurately fits the data and provides a reliable interpretation. This highlights the importance of carefully analyzing anomaly late-time voltage decay in TEM data, particularly in scenarios with moderately resistive backgrounds or deeply buried polarizable bodies. This study advocates for an approach that integrates IP effects to provide more accurate and reliable evaluations in regions with polarizable targets such as sulfides or clays.