Deep MT sounding using submarine cable voltages between the Gotland Island and the Swedish Mainland

Using potential variations over a large spacing, studies could be made on electric conductivity distribution deep in the Earth. The only submarine cable located within the ancient continental region is a Gotland cable in the Baltic Sea. The Gotland cable voltage time series are used for estimation of apparent resistivity and impedance phase in a period range up to one day. ID inversion of the observed transfer function is discussed. The conductivity structure obtained is close to the reference profile offered more than twenty years ago for the most ancient Karelian block of the Fennoscandian Shield as well as to the conductivity structure models constructed as a result the shield-wide magnetotelluric and magnetometer array study (BEAR project).