HR: 0800h
AN: GP11A-0819    [Abstracts]
TI: Project CMICMR: Long Period Magnetotellurics on Iceland
AU: * Golden, S
EM: golden@geophysik.uni-frankfurt.de
AF: Institute for Meteorology and Geophysics, University of Frankfurt, Feldbergstr. 47, Frankfurt/Main, D-60323 Germany
AU: Bj\"ornsson, A
EM: ab@unak.is
AF: Faculty of Natural Resource Sciences, University of Akureyri, Nordurslod, Akureyri, 600 Iceland
AU: Beblo, M
EM: beblo@geophysik.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, University of Munich, Theresienstr. 41, Munich, D-80333 Germany
AU: Junge, A
EM: junge@geophysik.uni-frankfurt.de
AF: Institute for Meteorology and Geophysics, University of Frankfurt, Feldbergstr. 47, Frankfurt/Main, D-60323 Germany
AB: The method of long period magnetotellurics can be used to determine the electrical conductivity distribution within the earth for depths reaching into the upper mantle. Knowledge of this conductivity distribution can provide important constraints for geodynamical models, complementing constraints derived from other, especially seismic, data. Earlier magnetotelluric studies by other authors give detailed insight into the conductivity distribution within the Icelandic crust, revealing e.g. a good crustal conductor beneath most of Iceland. However, they don't reach the upper mantle due to a limitation of their period range to less than 2000~s and the shielding effects of the good crustal conductor. To surpass this limitation three long period magnetotelluric field stations were set up on Iceland by Beblo and Bj\"{o}rnsson in 1999. To ensure the continuation of these measurements and to analyze and interpret the resulting data, a joint project between the universities of Akureyri (Bj\"{o}rnsson), Munich (Beblo) and Frankfurt (Junge) was initiated in 2001, titled ``Continuous Monitoring of the Icelandic Crust and Mantle Resistivity'' (CMICMR). Since the beginning of the project a huge data set has accumulated, mostly from the following field stations: Akureyri (2000--present), H\'{u}safell (2000--present), Skrokkalda (2000--2002), Gr\'{\i}mstadir (2002--present) and St\'{i}flisdalsvatn (fall~2003). The recorded time series are sampled at periods around 1~s and contain long continuous sections, some of them covering several months. While most of the stations used a conventional land based magnetotelluric instrument setup, the station St\'{\i}flisdalsvatn was an experiment to apply the method of lake bottom magnetotellurics for the first time in Iceland: the station used a prototype of the new data logger Geolore (Geophysical longtime recorder), which was developed at Frankfurt University, optimized for shallow under water applications. Recording the electric field components in the very stable environment of a lake bottom results in nearly drift free time series, hardly achievable by land based measurements. A number of people, K\"{o}nig, Salat and Golden, have worked on the analysis of the collected data. The most important result so far is a conductivity maximum at periods of about 5000~s, which can be explained by a good conductor in about 200--300~km depth. Two possible explanations for this conductor are partial melt within a plume head or enhanced melting at the ridge, but further modeling efforts are necessary to differentiate between these or other interpretations. On the poster an overview on the current state of the CMICMR project is given, with special emphasis on new results, such as those from the lake bottom experiment.
UR: http://www.geophysik.uni-frankfurt.de/em/icelmt/
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 0694 Instrumentation and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting