Woods Hole Oceanographic Institution

Dr Rob. L. Evans

»Electrical Structure of the Central Cascadia Subduction Zone: The EMSLAB Lincoln Line Revisited
»Electrical Lithosphere Beneath the Kaapvaal Craton
»Gulf Of Mexico Gas Seep
»MELT MT Results
»Wrightsville Beach Geophysics and Hydrology
»MELT Area Off-Axis Structure
»Karst Formation off North Carolina
»Review of Shallow Offshore EM Work
»Towed EM System
»EPR MMR Experiment
»Offshore MT and Subduction Systems
»Shallow Porosity Structure on the Continental Shelf
»Oceanic and Continental Mantle Resistivity
»New Jersey EM Survey
»Eel River EM Survey
»Impact of groundwater on EM data
»Electrical structure of Slave Craton
»Report of Shoreline Change Workshop

Rob L. Evans, Spahr C. Webb, and the RIFT-UMC Team, Crustal resistivity structure at 9 50'N on the East Pacific Rise: Results of an electromagnetic survey, Geophys Res Letts, vol 29, 2002

We report the first results of an extensive electromagnetic survey of the East Pacific Rise (EPR) at 9 50'N which used the magnetometric resistivity (MMR)technique to measure the electrical resistivity structure of the seafloor in the vicinity of the spreading center. Ten seafloor magnetometers were deployed in areas of known hydrothermal activity, in axial sites devoid of venting, and further off-axis to a distance of approximately 4 km. Data collected at offaxis sites show higher seafloor resistivities than at axial sites. This response is opposite to that expected from porosity controlled resistivity structure, with a thicker high-porosity extrusive layer 2A off-axis, as required by seismic data. An explanation for the reduced axial resistivities is that the uppermost few hundred meters of crust are much hotter beneath the ridge crest than a few kilometers off-axis, lowering the pore-fluid resistivity.

FILE » 2001GL014106_7966.pdf

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