P. Pushkarev

Magnetovariational Method in Deep Geoelectrics

Deep resistivity structure of the Earth’s crust and upper mantle can be studied by two natural-source methods: magnetotelluric (MT) sounding, which uses electric and magnetic field variations, and magnetovariational (MV) sounding, which uses magnetic field variations only. Integrated MT and MV data interpretation is a multicriterion problem. MT and MV data have different sensitivity to resistivity structures, as well as different robustness to their 2-D approximation. We consider two approaches to MT and MV data integrated interpretation: parallel inversion and successive inversions of data components. In the first case, the selection of weights of data components is critical. We suggest successive inversions approach and test it on model data, calculated for the schematic 2-D resistivity model of the Kyrgyz Tien Shan, and experimental data, collected along the profile in the Cascadia subduction zone.

Induction Sounding of the Earth’s Mantle at a New Russian Geophysical Observatory

Deep magnetotelluric (MT) sounding data were collected and processed in the western part of the East European Craton (EEC). The MT sounding results correspond well with impedances obtained by magnetovariation (MV) sounding on the new geophysical observatory situated not far from the western border of Russia. Inversion based on combined data of both induction soundings let us evaluate geoelectrical structure of the Earth’s crust and upper and mid-mantle at depths up to 2000 km, taking into account the harmonics of 11-year variations. Results obtained by different authors and methods are compared with similar investigations on the EEC such as international projects CEMES in Central Europe and BEAR in Fennoscandia.