Analysis of the Sign Reversal Phenomena in Grounded-Wire Transient Electromagnetic Response

Summary The transient electromagnetic response is significantly influenced by specific electrical structures and targets, which can lead to distortions and, in severe cases, sign reversal phenomena. Both resistive and conductive polarized targets can contribute to sign reversal. Accurate distinguishing the response characteristics associated with different electrical targets is crucial for enhancing our understanding of underground electrical structures and field exploration. However, systematic research on the causes of this phenomenon remains lacking. We analyzed the Yemaquan skarn-type mineral deposit in the East Kunlun orogenic belt of China as a case study. This mining area comprises resistive granodiorite and conductive, highly polarized carbonaceous rocks, making it an ideal site for investigating sign reversal phenomena. Through forward modeling, we discovered that the presence of low-resistivity and high-resistivity transitional interfaces underground can distort early-time responses, resulting in a numerical decrease in response. Conversely, polarized targets primarily induce sign reversal in late-time responses, indicated by an increase in response values. When resistive and polarized targets coexist, the response data may exhibit multiple sign reversal phenomena. Our conclusions were further validated through field measurement data.