Structural electrical anisotropy in the crust at the South-Central Chilean continental margin as inferred from geomagnetic transfer functions

Induction vectors, as a visualization of geomagnetic deep sounding transfer functions, display an unique pattern at the South Chilean continental margin between latitudes 38 degrees-41 degrees S and longitudes 71 degrees-74 degrees W: at long periods of approx. 3000 s their real parts are uniformly deflected from the W-E direction (which would be expected due to the coast effect and/or anomalies beneath the roughly N-S striking Andean mountain chain) to the NE. Attempts to model this behavior with simple and geologically realistic 3-D models failed, but a reasonable data fit was obtained by employing 2-D models with a structurally anisotropic, lower crust. This anisotropy hints at a deeply fractured, fluid-rich crust with a major strike direction of 40 degrees-50 degrees (SW-NE), oblique to the continental margin and in accordance with the regional stress field in the region of the volcanic arc. A surprising result is that the anisotropy persists in the forearc and may even reach until the continental slope near the trench. (c) 2008 Elsevier B.V. All rights reserved.