| Abstract |
Along with transient electromagnetics (TEM), the magnetotelluric (MT) method has been applied in recent decades to image subsurface resistivity, with deep conductive bodies frequently observed extending into geothermal reservoirs. However, acute resistivity contrasts close to shorelines significantly affect MT data: the measured responses may become significantly distorted compared to a forward response that would not account for this effect. This has the potential to bias the inverted resistivity features, which may result in hiding deeper subsurface features and obstruct geothermal exploration. In this work, the coastal effect is briefly reviewed and cases from geothermal prospecting in Iceland are discussed. Although the coastal effect is well understood in theory, its influence on more recent electromagnetic methods has not been fully explored in Icelandic geothermal contexts, since the increasing availability of high-resolution seafloor models, along with improved numerical tools, offers new opportunities to revisit and better understand these effects. This contribution provides a brief conceptual overview of the coastal effect, supported by forward modeling, illustrating how underlying low-resistivity structures could be masked in some cases. The results show how both past and future near-shore MT soundings can benefit from implementation of high-resolution bathymetric data. |