Toward reliable and high-resolution resistivity imaging with Controlled Source EM in land -densifying arrays as a key for success -10 years of progress for geothermal and mineral resources exploration

Abstract

The Controlled Source Electromagnetic (CSEM) method aims to image electrical resistivity at intermediate depths (0-3 km) for geothermal, mineral, and groundwater exploration. It was developed both as a deeper extension of DC resistivity (ERT) and as an active alternative to magnetotellurics (MT), capable of overcoming MT's limitations in challenging environments (noisy areas or weak natural signals). As demonstrated in marine settings, CSEM can provide high resolution and complementary illumination compared to MT. However, due to the significant logistical effort required for land deployment, most land-based CSEM surveys have used only a few transmitter positions (often one or two), effectively resembling CSAMT configurations. This limited source coverage results in poor resolution and unreliable resistivity models, where the acquisition footprint can be difficult to distinguish from actual geology. In this work, we review ten years of progress in land CSEM and demonstrate that dense arrays-with dozens to hundreds of synchronized sources and receivers-are key to achieving the high-resolution imaging originally expected. Despite greater logistical demands, we show that such surveys can be conducted with reasonable effort and cost, making them accessible for both industrial and academic applications. Furthermore, CSEM can be combined with MT at minimal additional cost, improving model constraints and reducing exploration risk.