EARTHSCOPE BACKBONE MAGNETOTELLURIC STATION AT BRANDEN, MISSOURI

The Earthscope program is a multiyear program to study the four-dimensional structure of the North American continent. A vital component of this program is USArray, which consists of a series of permanent and portable seismic, magnetotelluric and GPS recorders. The magnetotelluric portion consists of seven backbone (permanent) and twenty transportable systems. The transportable systems will be deployed in various regions of the US throughout the duration of Earthscope for a period of approximately one month and at a station spacing of approximately seventy kilometers. The backbone stations consist of a long period magnetotelluric system recording time-varying electrical and magnetic signals between 2 and 100,000 seconds. The seven backbone stations are located throughout the US with one being in the south-central US at Branden, Missouri. The Branden, Missouri station was partially installed in June, 2007 with two perpendicular electric field sensors with each dipole being approximately 300 meters long. A fluxgate magnetometer and data recording system (NIMS) were buried in separate 2 m deep vaults. Four hours of data were recorded to determine the noise levels at the site, which were found to be satisfactory. The installation of the permanent magnetotelluric recording equipment will occur in the Spring of 2007, and by the Fall of 2007 all backbone sites will be installed and running. The systems will telemeter data to a quality control and processing group, and then the processed data will be transmitted to the IRIS Data Management Center, where they will be freely available. These transportable and backbone magnetotelluric stations will provide the first systematic, continental-scale imaging of the electrical conductivity structure of the lower crust and upper-to-mid mantle in the US. When combined with the seismic array results, they will aid in determining the thermal, mineralogical and fluid makeup of the mantle and crust in the US. More information of the Branden site can be found at http://geosciences.missouristate.edu/faculty/Mickus/mtsparta.htm.