Estimating the Geoelectric Field and Electric Power Transmission Line Voltage During a Geomagnetic Storm in Alberta, Canada Using Measured Magnetotelluric Impedance Data: The Influence of Three‐Dimensional Electrical Structures in the Lithosphere

Estimating the effect of geomagnetic disturbances on power grid infrastructure is an important problem since they can induce damaging currents in electric power transmission lines. In this study, an array of magnetotelluric (MT) impedance measurements in Alberta and southeastern British Columbia are used to estimate the geoelectric field resulting from a magnetic storm on September 8, 2017. The resulting geoelectric field is compared to the geoelectric field modeled using the more common method that uses a piecewise‐continuous 1‐D conductivity model. The 1‐D model assumes horizontal layers, which result in orthogonal induced electric fields while the measured MT impedance data can account for fully 3‐D conductivity structure. The geoelectric field derived from measured MT impedance data is partially polarized in southern Alberta, and the geoelectric field magnitude is largest in northeastern Alberta where the resistive Canadian Shield outcrops. The induced voltage in the Alberta transmission network is estimated to be ∼120 V larger in northeastern Alberta when using the measured MT impedances compared to the piecewise‐continuous 1‐D model. Estimated voltages on transmission lines oriented NW‐SE in southern Alberta are 10%–20% larger when using the MT impedances due to the polarized geoelectric field. As shown with forward modeling tests, the polarization is due to a feature in the lower crust (20–30 km depth) called the Southern Alberta British Columbia conductor that is associated with a Proterozoic tectonic suture zone. This forms an important link between ancient tectonic processes and modern‐day geoelectric hazards that cannot be modeled with a 1‐D analysis. Plain Language Summary Solar activity creates a stream of charged particles that perturb the Earth's magnetic field leading to phenomena such as the Northern Lights. These perturbations in the geomagnetic field create geoelectric fields in the Earth. During periods of intense solar activity, strong geoelectric fields result in electric currents in power transmission lines which can cause power outages and damage to transformers. In this study, the geoelectric fields in Alberta during a geomagnetic storm are estimated using two different methods. The more common method assumes that the Earth consists of conductive layers while the other method incorporates the effects of 3‐D geological structures and lateral variations in conductivity. Results indicate that lateral variations in electrical conductiv