Leveraging Legacy Broadband Magnetotelluric Data for Geoelectric Field Hazard Assessment in Southern Italy

Geomagnetically induced currents (GICs) are a significant space weather hazard. Their accurate assessment requires estimating the geoelectric field, which depends on the Earth's subsurface electrical conductivity. While long‐period magnetotelluric (MT) surveys are ideal, archives of legacy broadband MT data, originally acquired for geological exploration, remain underused. We evaluate the feasibility of repurposing such data to reconstruct the geoelectric field during geomagnetic storms. Analyzing the two most intense storms of 2024 (May and October) using data from a broadband MT station in southern Italy, we combined the local MT impedance tensor with 1 Hz magnetic field data from the nearby Duronia geomagnetic observatory. Our analysis focused on the 2–8,000 s period band, critical for GIC assessment. To validate the modeled electric fields, we compared them with corresponding frequency components extracted from direct measurements using empirical mode decomposition. The modeled and observed fields show good agreement, confirmed by mutual information analysis, indicating statistically significant dependence, especially during storm main phases. We further show that reconstruction capability over the available impedance period range is storm‐dependent: for intense events, a tensor limited to ∼1,000 s may still provide a useful first‐order estimate, whereas for moderate storms the loss of long‐period content has a larger impact on accuracy. This demonstrates that legacy broadband MT data can provide quantitative estimates of geoelectric field components relevant to GIC hazard assessment, provided recordings are sufficiently long. Existing MT archives with extended acquisition times can represent a practical and cost‐effective resource for preliminary space weather hazard screening and historical studies.