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, Alan D. Chave and John R. Booker, On the importance of offshore data for magnetotelluric studies of ocean-continent subduction systems, Geophys. Res. Letts, vol 29, 2002

The presence of water in the mantle wedge overlying a subduction zone is expected to significantly enhance electrical conductivity, raising it above that of the cold subducting slab, or surrounding regions of dehydrated mantle. This suggests that magnetotelluric (MT) transects across subduction systems, measuring regional electrical conductivity structure, might be able to indirectly trace the pathways of water migration into the mantle. For ocean-continent subduction, it is logistically simpler to collect MT transects on the continental side of the system. However, we show that such land data are relatively insensitive to details of the electrical connections between the ocean and mantle. In contrast, seafloor measurements on the landward and seaward side of the trench are very sensitive to these electrical connections, and are essential to understanding the electrical structure of the entire subduction system. In particular, the conductivity structure of the hydrated mantle wedge overlying the slab can only be studied using offshore MT data.We demonstrate this result using a model of an ocean-continent system, although our results can be generalised to other subduction geometries.

FILE » 2001GL013960_7967.pdf

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