Missouri State
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Department of
Geography, Geology, and Planning
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The magnetotelluric (MT) site in SW Missouri is part of the EarthScope project (described below). The MT portion has two components: 1) a Backbone which consists of 7 long-period stations installed across the US as a reference network that will operate for the duration of the EarthScope Project (approx. 7-10 years) and 2) a Transportable component which is a mobile array of 20 long-period systems that will each be deployed for a period of 1 month in regions of scientific interest with a station-spacing of around 70 kms.
The MT data are collected as naturally-occurring time-varying Earth electrical and magnetic fields (see the example below). These fields can be combined to provide information about the Earth's electrical conductivity makeup which is most sensitive to the temperature and fluid content within the crust and mantle. Basically lower frequency data provides information deeper into the Earth (up to several ten's to hundred's of kilometers). The MT method is most sensitive to conductors in the crust and upper mantle. Silicate minerals (e.g., quartz) below melting temperatures are very resistive, so natural electrical currents are attracted to regions of low resistivity. Conductivities of silicate minerals in the mantle decrease with temperature, allowing estimates of temperature from MT soundings. Seismic properties of the crust and mantle can be used with electrical conductivity to allow discrimination of the type and state of crust and mantle. More information on the MT portion of EarthScope can be found at http://www.iris.edu/USArray/stationarrays.htm
EarthScope is a National Science Foundation Earth science program to explore the 4-dimensional structure of the North American continent. The EarthScope Program provides a framework for research on fault properties and the earthquake process, strain transfer, magmatic and hydrous fluids in the crust and mantle, plate boundary processes, large-scale continental deformation, continental structure and evolution, and composition and structure of the deep-Earth.
The nucleus of the Program is the EarthScope Facility, consisting of the Plate Boundary Observatory (PBO), the San Andreas Fault Observatory at Depth (SAFOD), and the USArray. The EarthScope Facility is a multi-purpose array of instruments and observatories that will greatly expand the observational capabilities of the Earth Sciences and permit us to advance our understanding of the structure, evolution and dynamics of the North American continent. The Facility is designed to continually incorporate technological advances in geophysics, seismology, magnetotellurics, geodesy, information technology, drilling technology, and downhole instrumentation. More information on the entire EarthScope Project can be found at www.Earthscope.org.
A rough overview of the installation are shown on the following 2 pages. Adam Schultz and Phil Taylor of Oregon State University, and Kevin Mickus and Melida Gutierrez of Missouri State University spent 4 days in June, 2006 installing the MT Backbone station. Two perpendicular electrical fields lines (300 meters long) where trenched and two 6 foot deep holes were drilled to store the 3-component magnetometer and the computer processor.
(click on image to see larger version) Preliminary Data (4 hours of magnetic and electrical fields) (PDF FILE)
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