USArray
A Continental-scale Seismic Observatory

Magnetotelluric Array

Summary

From 2006-2018, the EarthScope USArray magnetotelluric (MT) program collected observations of the Earth's naturally occurring electric and magnetic fields. These efforts were facilitated under a partnership between IRIS and Oregon State University (PI: Adam Schultz). 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 called the MT-Transportable Array (MT-TA) targeted regions identified by the MT science community (2006-2011 Pacific Northwest, 2011-2013 Mid-Continent Rift, 2014-2017 Eastern North America, 2017-2018 Northern Great Plains). The MT-TA stations were spaced in 70-km grids and operated continuously for several weeks, producing observations needed to resolve the conductivity structure of the crust and uppermost mantle. These observations may be integrated with other datasets to identify zones of fluid, melt, ores, and other markers that relate to the structure and evolution of the North American continent. Continuous telluric (ambient electric field) and geomagnetic field timeseries are available from IRIS and also processed into transfer functions that are available for for MT-TA and other contributed MT datasets. The USArray MT program also provided instruments and limited support (i.e. instrument preparation and data handling) for PI-driven Flexible Array (MT-FA) studies.

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), 20 stations in the Mississippi Embayment (late 2016), and 5 stations in the Great Plains (early 2017) as a complement to the MT-TA.
  • Under a supplemental award from the NSF to assist 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"

EarthScope MT completed its surveying efforts across the Great Plains in 2017-2018, filling in a large gap in coverage and creating a continuous swath of MT observations across two-thirds of the U.S.

 

 

Installing an MT-TA station (NDD28) near New Johns Lake, North Dakota on October 19, 2017.

Status Map

Footprints of MT-TA (by year), MT-BB, and MT-FA (iMUSHMOCHA onland, and MAGIC) stations that were operated from 2006-2018 during EarthScope. Click to enlarge

MT After EarthScope

Under the "Seismological Facilities for the Advancement of Geoscience" award from NSF (2018-2023), IRIS is establishing comprehensive PI support to use MT instruments from the PASSCAL Instrument Center. In addition, a grant from NASA is supporting continued regional MT surveys in the southwestern U.S. Andy Frassetto serves as the MT Program Manager at IRIS overseeing these activities. The scientific goals of the NSF- and NASA-funded MT activities are advised by members of the MT science community serving on the Electromagnetic Advisory Committee (EMAC), chaired by Ninfa Bennington.