The conductivity of the solid Earth, and of its seas, plays a critical role in mediating the risk that space weather poses to electrically grounded infrastructures, most obviously the transmission grids that enable electrical power to be transported over long distances. These grids are vital for modern energy systems as we exploit power sources (e.g. wind, solar, hydro, nuclear) that are often distant from population centers.
However, over the past 80 years, we have learned that grid operations can be disrupted when geomagnetic storms induce significant electric fields at the surface of the Earth. The size of those fields is strongly dependent on ground conductivity and on proximity to highly conducting sea water.
Marshalko et al.  use a range of conductivity models to estimate the geoelectric fields induced in the eastern United States by a moderate magnetic storm. These models include both realistic and simplified models of the 3D conductivity structures within the Earth, as well as changes in sea conductivity arising from variations in sea depth.
The results confirm that there are strong enhancements of the geoelectric field close to coasts, and also arising from inhomogeneities in ground conductivity. These enhancements contribute significantly to the voltages that arise from integration of geoelectric fields (as along grid lines), showing the importance of 3D conductivity when assessing space weather risks to transmission grids.
The results highlight that the enhancement of geoelectric fields has a component parallel to the coast, as well as perpendicular to the coast. Thus, it has potential to impact grounded infrastructures (e.g. grid lines, pipelines, rail systems) where these run parallel to coasts (a common occurrence due to land topography and focusing of population centers near coasts).
Citation: Marshalko, E., Kruglyakov, M., Kuvshinov, A., Murphy, B. S., Rastätter, L., Ngwira, C., & Pulkkinen, A. . Exploring the influence of lateral conductivity contrasts on the storm time behavior of the ground electric field in the eastern United States. Space Weather, 18, e2019SW002216. https://doi.org/10.1029/2019SW002216
—Michael A. Hapgood, Editor, Space Weather