Anisotropy and phase splits in magnetotellurics

摘要: Abstract Several recent papers suggesting that the electrical conductivity of lower crust and upper mantle are anisotropic have been based upon magnetotelluric (MT) observations ‘phase splits’, MT analogue shear wave splitting. The emphasis on phase rather than amplitude-response results from distorting effect variations in overlying crust. These distort amplitude response deeper levels make inferences difficult. At long periods needed to probe at upper-mantle depths, response, a tensor, is negligibly affected by small scale However, half-space with uniform but independent polarization direction no split occurs. Using simple layered models we demonstrate produced change interface between isotropic layers; maximum difference reflecting contrast (gradient) principal conductivities layer layer's conductivity. In general case, where none axes lie plane surface, orientation which occurs (i.e. axis tensor) determined horizontal projection tensor's ellipsoid. such cases will not be aligned parallel any axes. splits consequence spatial differences or gradients conductivity, intrinsic bulk properties (tensor) itself this respect fundamentally different