Multi-component 3D Inversion of Magnetotelluric Data from Northen Scandinavia

Abstract:

The Magnetotellurics (MT) in the Scandes (MaSca) project aims to bridge the gap of MT measurements in the north-west Fennoscandian Shield. The project focuses on the study of the electrical conductivity structure of the crust and upper mantle. An array of 70 synchronous long period and 236 broad-band MT sites were occupied in summers 2011 to 2013. Large synoptic arrays allows to estimate different magnetotelluric transfer functions, including inter-station transfer functions. We have run 3D inversion using Modular EM system of full impedance tensor, tipper vector and perturbation tensor simultaneously. As a result we have obtained more geologically meaningful results as compared to single transfer function inversion. The final model has less sharp details (smaller model norm). The presence of magnetic transfer functions makes inversion less prone to galvanic distortion influences. The array is located in high latitudes, hence the source field effect might be affecting estimates of transfer functions. In order to reduce the effect we have applied multivariate processing techniques to estimate all the transfer functions. Perturbation tensor is most noticeably affected by the source field therefore we had to exclude some sites and periods from the inversion to improve data fit. Overall we have obtained a consistent data fit for all the transfer functions.