Magnetotelluric Array

Summary

Since 2006, the EarthScope USArray magnetotelluric (MT) program has facilitated observations of the Earth's naturally occurring electric and magnetic fields. A backbone network consisting of seven stations (MT-BB) provided reference observations across the United States from 2008-2015. In addition, yearly campaigns of temporarily deployed instruments call the MT-Transportable Array (MT-TA) have targeted areas identified by the MT community (2006-2011 in the Pacific Northwest, 2011-2013 in the Mid-Continent Rift, 2014-2017 Eastern North America). These stations were spaced in an approximate 70-km grid and operated for around three weeks to resolve the conductivity structure of the crust and uppermost mantle. These observations are often integrated with other geophysical data to identified zones of fluid, melt, ores, and other markers bearing on the structure and evolution of the North America. Data are archived with IRIS and processed into transfer functions that are available for for MT-TA and other stations. The USArray MT program also provides instruments and limited support (i.e. instrument preparation and data handling) for PI-driven Flexible Array (MT-FA) studies.

The MT instruments are operated and maintained by the National Geoelectromagnetic Facility at Oregon State University under a subaward (PI Adam Schultz) from IRIS. Andy Frassetto serves as the MT program lead at IRIS. The scientific and operational goals of the MT program are overseen by members of the EarthScope community serving on the Electromagnetic Advisory Committee (EMAC), chaired by Rob Evans.

Key Developments

With approval from NSF, six of seven MT-BB stations (excluding the Blacksburg, VA site) have been decommissioned and their instruments have been converted for temporary deployment.
The 2014-2018 EarthScope MT Siting Plan was adopted by the EMAC, finalizing the remaining targets for the MT-TA during EarthScope.
The USGS deployed 22 MT stations in Florida (early 2015) and 20 stations in the Mississippi Embayment (late 2016) as a complement to the MT-TA.
Under a supplemental award from the NSF reflecting the National Space Weather Action Plan, MT-TA stations were collected across New England in 2016-2017, which completed MT-TA along the Eastern Seaboard.
The EMAC, in consultation with IRIS governance and MT-program management at IRIS and OSU, has approved a change in the MT Siting Plan to work in the Great Plains at full spacing during the 2017-2018 field campaigns.

The "Golden Spike"

Stations planned for operation in 2017-2018 across the Great Plains will connect MT-TA footprints collected separately over the previous decade of EarthScope MT. This will create a continuous swath of MT observations across a large portion of the U.S. We anticipate the completion of field operations in late 2018. As opposed to recent years working on the East Coast, stations in the Dakotas collected during the fall of 2017 offer comparatively more solitude!