Determining the electrical conductivity tensor of the lithosphere of the Baltic Shield

Data of magneto variational sounding (MVS) under the IMAGE (International Monitor for Auroral Geomagnetic Effects) project and data of magnetotelluric sounding (MTS) under the BEAR (Baltic Electromagnetic Array Research) project are processed with consideration of the lateral inhomogeneity of the electromagnetic field in order to fully determine the components of the electrical conductivity tensor of Baltic Shield rocks. In the reconstruction of the anisotropy characteristics from the MVS and MTS data, an approximate domain description of the bounded polygon area with an effective electrical conductivity tensor is used. Maps of the lateral distributions of its eigenvalues and the strikeazimuth of maximum electrical conductivity are constructed. According to available experimental data, an azimuth angle of 40°-60° bestdescribes the direction of the principal axis of the tensor with maximum electrical conductivity on the Baltic Shield. Comparison of the results obtained from seismic and electromagnetic data indicates a possible correlation between the strike azimuths of maximum electrical conductivity and low seismic velocities, as well as similarity of the boundaries of the corresponding domain structures of the Baltic Shield.