The Gradient Magneto-Telluric Method at the Sea Floor

The magneto-telluric method is a technique used to estimate earth resistivity profiles and can theoretically be implemented either by measuring electric and magnetic field components or by measuring magnetic gradients and magnetic field components. The gradient method, although theoretically possible, is impractical at the atmosphere-earth interface because the magnetic gradients associated with the naturally occurring ULF magnetic field fluctuations are very weak (on the order of 10-10 pT/m). In this paper, the gradient method is analyzed at the sea-seafloor interface and is shown it is practical because the vertical gradients are much stronger (on the order of 10 pT/m) so they can be detected with sensitive magnetic gradiometers such as superconducting gradiometers. If successfully developed, this technique will provide a practical approach to the determination of seafloor resistivity with compact, i.e., local field sensing, instrument packages.