GNGTS 2018 - 37° Convegno Nazionale

592 GNGTS 2018 S essione 3.1 GEUS in 2017 (Viezzoli et al. , 2018). The lithostratigraphic formations observed in this section (Fig. 3, upper panel) are, from below: (1) the Buckinghorse Formation and (2) the Sikanni Formation. On top of these formations, the Quaternary sediments display a degree of vertical variations in resistivity due to the presence of internal heterogeneous structures. The derived geological interpretation using the sharp inversion is characterized by: fully resolved layers thickness within the glacial cover; well resolved small hill structures in the middle of the modern valley, formed by glaciolacustrine deposits; clear resistive response from the heterogeneous bedrock formation; an uncertain interpretation of the lower boundary of Buckinghorse Formation. What is below the Buckinghorse has therefore not been interpreted. Conclusions. The smooth approach may produce suitable models in environments where material properties vary gradually. The few layers approach is useful in models with simple geological geometries whereas the sharp approach provides a good combination of the two. The sharp model is capable of providing compact resistivity structures separated by clear contacts. This makes much easier the identification of the petrophysical interfaces, and, in turn, facilitates their subsequent geological interpretation. The derived preliminary geological interpretation of the cross section in Fig. 3 (LCI inversion result) does not take into account resistivity variations within the glaciofluvial deposits (“gfd” Quaternary unit, Fig. 3). On the other hand, the geological interpretation carried out by GEUS is based on a smooth- SCI inversion. In this type of inversion model parameter information migrates horizontally through spatial constraints, increasing the resolution of layers (Viezzoli et al., 2008). Therefore, in order to locate and map buried valleys within the Quaternary coverage, the quasi-3D SCI sharp inversion has been carried out. We have obtained different reasonable 3D sharp-models that have been used to improve the final geological interpretation. References Auken, E., Christiansen, A.V., Westergaard, J.H., Kirkegaard, C., Foged, N., Viezzoli A.; 2009: An integrated proces- sing scheme for high-resolution airborne electromagnetic surveys, the SkyTEM system. Exploration Geophysics 40, pp. 184–192 Jørgensen F., Menghini A., Juhl Kallesøe A., Vignoli G., Viezzoli A., Pedersen S.A.S; 2016: Structural geology of folded terrain in the Rocky Mountains’ foothills interpreted from SkyTEM. A preliminary study of SkyTEM data collected in the Peace region, NE British Columbia, Canada in ”Danmarks og Grønlands Geologiske undersøgel- se rapport 2016\34”, pp. 2-21. Viezzoli, A., Christiansen, A. V., Auken, E., Sørensen, K.; 2008: Quasi-3D modeling of airborne TEM data by spatial- ly constrained inversion: Geophysics, 73(3), pp. F105-F113. Viezzoli A., Menghini A., Jørgensen F., Høyer A.S.; 2018: Processing and inversion of SkyTEM data leading to a hydrogeological interpretation of the Peace River North-Western Area. Report 2018-06, pp. 2-27. Freely down- loaded from Geoscience BC website: http://www.geosciencebc.com/s/PeaceProject.asp Vignoli G., Sapia V., Menghini A., Viezzoli A.; 2017: Examples of improved inversion of different airborne elec- tromagnetic datasets via Sharp Regularization. Journal of Environmental and Engineering Geophysics, 22, pp. 51-61. Vignoli, G., Fiandaca, G., Christiansen, A. V., Kirkegaard, C., Auken, E.; 2015: Sharp spatially constrained inversion with applications to transient electromagnetic data. Geophysical Prospecting, 63(1), pp. 243-255. Zhdanov, M. S.; 2002: Geophysical inverse theory and regularization problems. Elsevier Science & Technology.