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Abstract

Geomagnetically Induced currents (GICs) arise from rapid geomagnetic field variations caused by highly energized solar wind. These currents flow in the Earth's surface and along conductive man-made infrastructures galvanically connected to Earth, as power systems. Consequently, electric power stability can be compromised and, in extreme cases, can lead to blackouts.Accurate GIC simulations require knowledge of the geomagnetic field variations, the Earth's conductivity, and power grid parameters. To accurately estimate the magnitude of GICs, we need to understand how the conductivity model is affected by geological structures. Testing various conductivity models (e.g., tighter magnetotelluric sounding grid and presence/absence of specific geological structures) can determine the sensitivity of our GIC calculations to different geological structures. This information is vital in accessing the realistic hazard to specific substations of power grids.Additionally, GIC measurements can be used to improve the conductivity model. Since August 30th 2021, we have been monitoring GIC currents flowing through a transformer's neutral at Paraimo (SPI) substation. Comparing with simulations, we noticed a deterioration of correlation at lower frequencies, indicating imprecision of our conductivity model for deeper layers. Given the availability of geomagnetic (at the nearby observatory of Coimbra) and GIC measurements, we can carry on different tests and estimate a local surface impedance. Then, we can invert it to try to extract the 1D ground conductivity structure at depth, using standard MT tools [1,2].[1] 10.1109/UPEC50034.2021.9548157[2] https://doi.org/10.1186/BF03352040