Coast effects on magnetic and magnetotelluric transfer functions and their correction: application to MT soundings carried out in SW Iberia

The coast effect on magnetic and magnetotelluric data acquired near the SW coast in the Iberian Peninsula was investigated using three-dimensional modelling. The ocean was modelled as a layer with constant conductivity (0.3 ohm m) and thickness of 3.5 km. The continental resistivity model was constructed taking into account its electrical structure obtained from previous magnetotelluric studies. The model shows that the ocean-coast effects are important for periods greater than 100–300 s (in this case), affecting both the induction vectors and the impedance tensors. A method for the correction of the coast effects on the impedance tensor is presented. Synthetic data generated from a model including coast effects were corrected using the method and compared successfully with data not showing those effects. As an example the correction has been applied to some magnetotelluric soundings carried out in SW Iberia.