HR: 16:15h
AN: GP34A-02    [Abstracts]
TI: An Amphibious Magnetotelluric Study at the South Chilean Continental Margin
AU: * Brasse, H
EM: h.brasse@geophysik.fu-berlin.de
AF: FU Berlin - FR Geophysik, Malteserstr. 74-100, Berlin, 12249 Germany
AU: Kapinos, G
EM: kapinosg@geophysik.fu-berlin.de
AF: FU Berlin - FR Geophysik, Malteserstr. 74-100, Berlin, 12249 Germany
AU: Li, Y
EM: yuguo@ucsd.edu
AF: Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0225 United States
AU: Chave, A
EM: alan@whoi.edu
AF: Woods Hole Oceanographic Institution, Deep Submergence Laboratory MS#7, Woods Hole, MA 02543 United States
AB: A large network of long-period magnetotelluric sites was operated in the southern Chilean Andes between latitudes 37.5--41°S. It consists of 3 profiles from the coast of the Pacific Ocean to the volcanic arc, several connecting sites and more detailed investigations around active Villarrica and Llaima volcanoes. In 2004/2005 one profile was extended with sea-bottom stations across the trench towards the Pacific plate as part of the multi-disciplinary TIPTEQ programme. While analysis of offshore data is still ongoing, the onshore data display an unexpected first-order effect: without exception real induction vectors at all sites point consistently NE for long periods over the whole study area, overprinting any other effect which might be connected to conductivity anomalies along the N10°E striking continental margin. While 3-D models with realistic geometries cannot account for this highly anomalous behavior of tippers, quite simple 2-D models incorporating anisotropy explain the data at least qualitatively. The ocean (modeled with crude bathymetry) accounts for the large tipper magnitudes, while an anisotropic layer in the upper-middle crust is responsible for the deflection of vectors. The direction of the highly conductive axis is NW-SE, in good agreement with the multitude of fault systems observed at the surface in the forearc and arc regions. The South Chilean crust has thus to be considered as deeply fractured with far-reaching consequences for migration of fluids and melts, where appropriate conditions exist.
DE: 0905 Continental structures (8109, 8110)
DE: 0925 Magnetic and electrical methods (5109)
DE: 1020 Composition of the continental crust
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1515 Geomagnetic induction
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005