Tensor Decomposition with Static Shift Correction of the Deep Magnetotelluric (MT) Soundings to Improve the Asthenospheric Depth Values in the Great Hungarian Plain

Abstract

26 deep — broadband — magnetotelluric soundings (MTS) have been carried out in the Eastern part of Hungary in the Great Hungarian Plain. These MT soundings aimed first of all at the determination of the structure of the conducting asthenosphere besides the study of the surface sedimentary cover. As the greater part of the MTS curves are distorted by the basement relief their magnetotelluric structural anisotropy could generaly be high.

Groom-Baily (GB) decomposition has been applied to reduce the 3D near-surface effect to decrease so the structural anisotropy. It resulted in the decrease of the MT anisotropy from 1.5 to 1.1 in a statistical sense. The GB distortion parameters — shear and twist — are in average between 7° and 11° (absolute values). The deviation between the asthenospheric map calculated on the basis of the original ID asthenospheric depths and that obtained after decomposition is relatively small. Besides the decomposition the static shift should have been taken into account because the GB decomposition did not do it. As conclusion the paper gives a corrected asthenospheric map — as a present state of this kind of investigations — for the Great Hungarian Plain with average depth of about 60 km in agreement with the early value of the author from 1963. In addition Bahr’s decomposition parameters have been computed to check the GB strikes in selected sites.