Detection of 3-D inhomogeneities of the medium at magnetotelluric sounding in the Arctic (numerical experiment)

Abstract

SUMMARY The magnetotelluric sounding (MTS) conducted on drifting ice floes in the Arctic is of particular interest for detection of 3-D inhomogeneities in crustal conductivity. Their manifestations in behaviour of standard magnetotelluric curves are shielded by the well conducting layers of seawater and sediment. As target objects, these inhomogeneities are shown as small changes (only hundredths of per cent) in apparent resistivity, and as very weak variations of vertical magnetic field component. Therefore, accounting for additional data on the vertical electric field component or the electric field potential of the transverse magnetic (TM) mode is of interest. For recording the TM-mode potential, we offer to use the circular electric dipole (CED) located on the ice surface as a receiver in MTS. We investigate possibilities of crustal 3-D inhomogeneity detection using the TM-mode potential received with the CED. A numerical experiment showed that the potential of electric field of the TM-mode on the ice surface reaches values suitable for detection. Examples of the inverse problem solution using synthetic data on the TM-mode field are presented. We found that the information on the depth of 3-D object could be obtained by the analytical continuation of the profile data on the TM-mode potential. Using the MTU-5 Phoenix Geophysics stations for the CED system, we carried out preliminary measurements on the ice surface on the Ob river. We checked the measurement results of the TM-mode potential using the MTS data obtained earlier near the CED system. We compared results of the TM-mode potential calculation for the found 3-D-medium model to the CED experimental data. Our results showed that the potential dependences on the period measured by the СED and those obtained for the 3-D model have similar characteristics. We believe recording the TM-mode potential in the Arctic allows to reveal the existence and characteristics of crustal conductivity 3-D heterogeneities.