IRIS has partnered with Oregon State University to collect regional magnetotelluric (MT, see Kelbert et al. for more details) surveys across the contiguous United States. This effort utilizes a pool of long-period MT instruments that are owned by the National Science Foundation (NSF) and maintained by OSU and the PASSCAL Instrument Center. During 2019 and 2020 we are operating MT stations in parts of California, Nevada, Arizona, and Utah (see map) under a grant from NASA's Heliophysics Science Division. These activities extend observations made by the NSF-EarthScope USArray MT Transportable Array.
EarthScope MT observations were used to study different geologic features and processes across North America, but have become critical to help characterize the hazard to human infrastructure posed by the interaction of space weather with a variability conductive subsurface. Strong geomagnetic storms can interact with resistive regions of the lithosphere to generate electric currents that overwhelm utility assets, such as the electric power grid. A Presidential Executive Order in March 2019 resulted from the growing awareness in the Federal government to the hazards posed by geomagnetically induced currents (GICs). These issues are discussed in the 2015 National Space Weather Stategy and National Space Weather Action Plan and an updated 2019 National Space Weather Strategy and Action Plan. The Executive Order calls for the completion of MT surveying across the contiguous U.S. by 2023, which would significantly improve the characterization of hazards from GICs. The NASA surveys are the first step in accomplishing this task.
Above: Completed EarthScope (white), USGS (yellow), and NASA (red) MT stations with NASA sites planned for 2020 (open)
Below: Installation of an MT station in the Mojave Desert, CA in spring 2019