Theory and Application of a Short-Offset Transient Electromagnetic Method

The electromagnetic (EM) method constitutes a geophysical technique grounded in the principles of electromagnetic induction. This approach involves scrutinizing and interpreting the responses of the Earth, induced by either natural or artificial electromagnetic sources, to discern the electrical characteristics and spatial distributions of subsurface structures. Traditional artificial-source Transient Electromagnetic (TEM) methods rely on a plane-wave approximation theory, necessitating long offsets that yield weak signals and low resolution. In practical on-site scenarios, exploring near-source areas becomes feasible with appropriate transmitting waveforms and observational techniques. Short-offset grounded-wire Transient Electromagnetic (SOTEM) methods employ discontinuous square wave currents, utilizing long grounded-line sources and short offsets within twice the detection depths to capture pure secondary field signals. In this study, a case study conducted in Xiaoshan, Henan province, is presented to showcase the practical application of SOTEM. The findings reveal that SOTEM methods offer high detection accuracy, large detection depths, convenient and efficient construction, and suitability for application in mountainous terrains. Therefore, the study concludes that employing SOTEM methods is well-suited for deep mineral resource exploration.