Abstract: Geomagnetic storms can cause power grid instabilities and blackouts due to excessive geomagnetically induced currents (GICs) flowing in electric transmission systems. In this study, we assess regional vulnerability to GICs by modeling the geoelectric fields induced by significant historic geomagnetic disturbance events in the presence of 3D subsurface geology using data from the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) magnetotelluric array, Australia‐Wide Array of Geomagnetic Stations (AWAGS) magnetometer array, and Geoscience Australia geomagnetic observatory network. We analyze the vertical component of the magnetic field with respect to the horizontal magnetic‐field polarization for two magnetic storms and gain insight into the inductive effects associated with field polarization orientations in the 3D case. We also analyze the telluric field intensity and polarization for a unit geomagnetic field polarized in northerly and easterly directions at AusLAMP sites and find that in the presence of 3D geology the induced field has a very polarization‐sensitive anomaly. We model the geoelectric fields in southeastern Australia for the 1989 “Québec storm.” The induced ground electric fields are typically in the range 1,000–2,000 mV/km with a few sites within 2,000–5,000 mV/km on highly resistive regions and in coastal areas, and below 300 mV/km on inland sedimentary basins. The current study focuses on magnetic field variations with periods between 120 and ~20,000 s due to bandwidth limits in our magnetotelluric tensor data and the Nyquist limit for the 60 s sampling of our geomagnetic‐field data. Hence, our modeled maximum values should be considered lower estimates of potential real values. Plain Language Summary: We assess Australia's vulnerability to electric currents caused by geomagnetic storms. We use data from recent and historic geophysical studies to represent a range of possible geomagnetic‐field variations (including the extreme 1989 “Québec storm” event), and we use a three‐dimensional mathematical representation of the electrical conductivity of Australia's regional geology to represent the natural conductors in which electric currents can flow. Our analysis shows that the spatial variability of ground electric currents that can be caused by geomagnetic storms is closely associated with geologic structure. We find that ground electric currents are stronger in places where there are large differences between the conductivities of subsurface geologic structures. These include, for example, electrically resistive rocks near coastlines that are adjacent to deep and highly conductive oceans or, inland, where there are big contrasts between the electrical conductivities of different rock types. Away from such natural differences in electrical conductivity ground electric currents tend to be weaker. Every country on Earth has different types of rock that make up its geology, and many countries are bounded by an ocean. Vulnerability to electric currents caused by geomagnetic storms is an increasingly important issue, particularly in light of the mushrooming reliance of societies on high‐tech solutions to modern needs. The method we have developed for this research is readily extensible to other places to assess the risk posed by ground electric currents. <b>Citation:</b> Wang, L., Duan, J., Hitchman, A. P., Lewis, A. M., & Jones, W. V. (2020). Modeling geoelectric fields induced by geomagnetic disturbances in 3D subsurface geology, an example from Southeastern Australia. <i>Journal of Geophysical Research: Solid Earth</i>, 125, e2020JB019843. https://doi.org/10.1029/2020JB019843

The surface electric field induced by external geomagnetic source fields is modeled for a continental-scale 3-D electrical conductivity model of Australia at periods of a few minutes to a few hours. The amplitude and orientation of the induced electric field at periods of 360 s and 1800 s are presented and compared to those derived from a simplified ocean-continent (OC) electrical conductivity model. It is found that the induced electric field in the Australian region is distorted by the heterogeneous continental electrical conductivity structures and surrounding oceans. On the northern coastlines, the induced electric field is decreased relative to the simple OC model due to a reduced conductivity contrast between the seas and the enhanced conductivity structures inland. In central Australia, the induced electric field is less distorted with respect to the OC model as the location is remote from the oceans, but inland crustal high-conductivity anomalies are the major source of distortion of the induced electric field. In the west of the continent, the lower conductivity of the Western Australia Craton increases the conductivity contrast between the deeper oceans and land and significantly enhances the induced electric field. Generally, the induced electric field in southern Australia, south of latitude −20°, is higher compared to northern Australia. This paper provides a regional indicator of geomagnetic induction hazards across Australia. <b>Citation:</b> Wang, L., A. M. Lewis, Y. Ogawa, W. V. Jones, and M. T. Costelloe (2016), Modeling geomagnetic induction hazards using a 3-D electrical conductivity model of Australia, <i>Space Weather</i>, 14, 1125–1135, doi:10.1002/2016SW001436