Geoelectric hazards generated by a nuclear explosion at the outer edge of Earth’s atmosphere can be strongly affected by the electrical conductivity of rock structures beneath the Earth's surface, according to a study led by the U.S. Geological Survey.
Down to Earth: Complexities of Geology Affect Nuclear Electromagnetic Pulse Hazard
In collaboration with partners at the University of Colorado, USGS researchers used new geophysical survey data to examine a scenario of a nuclear explosion. The scientific investigation was undertaken in response to a March 2019 Executive Order that mandates research into geomagnetic variations associated with electromagnetic pulses (EMPs).
Scientists have known for decades that an EMP can be generated by the action of a high-altitude nuclear explosion on the atmosphere. A low-frequency part of the EMP signal, E3, can induce electric fields in the conductive solid Earth. These geoelectric fields, in turn, can interfere with the operation of electricity power grids. Recognizing the threat posed by EMP weapons, the U.S. Department of Energy, the Department of Defense, the Department of Homeland Security, and the commercially supported Electric Power Research Institute have developed strategies to improve the understanding of the EMP threat to the U.S. national electric power grid.
The study examines a scenario involving an explosion of several hundred kilotons set several hundred kilometers above the eastern midcontinental United States. Using new detailed survey measurements, the investigators show that the surface electromagnetic properties of the solid Earth in this region are geographically complicated, a characteristic that is reflective of the electrical conductivity of underlying rock structures. The researchers also show that these properties of the solid Earth strongly distort the E3 geoelectric field that would impact the region’s electricity power grid system.
The lead author of the report, USGS geophysicist Jeffrey J. Love, notes, "Extremely simple Earth models, such as those now widely used in government and industry reports on power-grid vulnerability, cannot provide accurate estimates of EMP hazards in complex geological settings. Until the effects of the solid Earth are properly accommodated, EMP hazards to the Nation's power grid are not being accurately evaluated."
The USGS Geomagnetism Program provides continuous and real-time records of geomagnetic field variations; disseminates magnetic data to governmental, academic, and private institutions; and conducts research into the nature of geomagnetic variations for purposes of scientific understanding and hazard mitigation.
Love, J. J., Lucas, G. M., Murphy, B. S., Bedrosian, P. A., Rigler, E. J. and Kelbert, A., 2021. Down to Earth with nuclear electromagnetic pulse: Realistic surface impedance affects mapping of the E3 geoelectric hazard, Earth and Space Science, doi:10.1029/2021EA001792.