Geoelectric hazard maps for the continental United States

Abstract

In support of a multiagency project for assessing induction hazards, we present maps of extreme‐value geoelectric amplitudes over about half of the continental United States. These maps are constructed using a parameterization of induction: estimates of Earth surface impedance, obtained at discrete geographic sites from magnetotelluric survey data, are convolved with latitude‐dependent statistical maps of extreme‐value geomagnetic activity, obtained from decades of magnetic observatory data. Geoelectric amplitudes are estimated for geomagnetic waveforms having 240 s sinusoidal period and amplitudes over 10 min that exceed a once‐per‐century threshold. As a result of the combination of geographic differences in geomagnetic activity and Earth surface impedance, once‐per‐century geoelectric amplitudes span more than 2 orders of magnitude and are an intricate function of location. For north‐south induction, once‐per‐century geoelectric amplitudes across large parts of the United States have a median value of 0.26 V/km; for east‐west geomagnetic variation the median value is 0.23 V/km. At some locations, once‐per‐century geoelectric amplitudes exceed 3 V/km.

Geoelectric Hazard Maps for the Pacific Northwest

“…In Figure c, we compare our hazard estimates with those obtained previously for the continental United States (Love & Bedrosian, ; Love et al, ). Whereas, we calculate the 1‐min E h analyzed here by convolving geomagnetic time series with magnetotelluric impedances, the hazard maps for the continental United States were indirectly derived: a statistical analysis was performed of historical global geomagnetic variation in terms of the amplitudes of waveforms having specific periods and polarizations and persisting for a given duration of time; the waveforms were convolved with magnetotelluric impedances from various survey sites.…”

Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

“…These include Bedrosian and Love (2015), who use 3-dimensional magnetotelluric EarthScope impedances to estimate the geoelectric response of a simulated time-varying geomagnetic field across northern North America. Love et al (2016a) used these impedances to produce a hazard map of half of the USA by convolving these impedances against latitudedependent maps of extreme geomagnetic activity. Torta et al (2017) improved the estimate of the phase and magnitude of measured geomagnetically induced currents (GICs) in power transmission systems by modeling local 2-and 3-dimensional conductivity structures with their impedances.…”

Rapid prediction of electric fields associated with geomagnetically induced currents in the presence of three‐dimensional ground structure: Projection of remote magnetic observatory data through magnetotelluric impedance tensors

“…This is not the case for a 1‐D conducting Earth. Furthermore, ground electric fields resulting from a GMD of a given magnitude and source magnetic field orientation can be intensified substantially (by up to an order of magnitude) for the 3‐D case relative to the 1‐D case [ Thomson et al ., ; Bedrosian and Love , ; Love et al , ] and can vary dramatically in direction and intensity from one GMD to another since the time‐frequency content of source field intensity and orientation is unique to each GMD. An important consequence of this is that no general linear scaling exists between the ground electric fields predicted from a GMD acting on a 1‐D conductivity model and those predicted from a 3‐D model.…”

“…There is growing recognition that the electrical conductivity of the crust and mantle varies strongly in all three spatial dimensions [ Kelbert et al ., ; Meqbel et al ., ; Schultz et al ., ; Evans et al ., ], and that 3‐D conductivity variations can lead to significant intensification of ground electric fields [ Thomson et al ., ; Bedrosian and Love , ; Love et al , ]. Solutions to calculating ground electric fields in the time domain that are related to GMDs for the coupled ionospheric‐Earth 3‐D induction problem often employ finite difference time domain solutions in massively parallel computing environments [e.g., Simpson , ].…”