GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.1 591 depth of 300 m. The model b loses sensitivity in the central part, below the conductive layer (Buckinghorse). The starting model of the few-layers inversion was parameterized with 3 layers and a homogeneous half-space of 100 Ωm (Fig. 2, left panels, c). The few-layers approach can resolve boundaries of glaciofluvial deposits but, it is not able to fully resolve the structure of glaciolacustrine deposits. The model loses sensibility for the Nordegg Formation. The data Misfit is generally acceptable except in the left part of the profile. Locally the model does not fit the data. The sharp inversion is parameterized with 30 layers (β1=27, β2=15, σH=2%, σV=10%, refer to Vignoli et al. , 2014) and a homogeneous half-space of 100 Ωm is used as starting model. The sharp is clearly the most effective one in terms of reconstruction of geometries and retrieval of the correct resistivity values. The response of the strongly resistive formation (Nordegg) is clear as well as the lower contact of the Buckinghorse Formation. Results on real data. 30% of the cross sections, located in the Area 1, have been inverted. The settings are the ones tested in the synthetic modelling. The inversion results gradually change (Fig. 2, right panels), passing from models that do not fit adequately the data but are capable of discerning basic resistivity structures, to models rich-in detailed resistivity features, but, at the same time, capable of reconstructing blocky solutions. We start from a simple model made up of few main blocks with different resistivity values to detailed geophysical model with quasi-smooth resistivity variations. The details of sharp inversion on a selected cross section are shown below. A rough geological interpretation has been undertaken on cross section “A” (sharp model n.4 in Fig. 2) starting from the geological interpretation (Fig. 3, lower panel) carried out by Fig. 3 - Upper panel: Cross sections A: geological interpretations of the sharp result. Bedrock formation boundaries are delineated by thick grey lines. Interpretations in the drift succession are delineated by thin black dotted lines. Models are shaded with DOI and show associated data misfit (red line). Lower panel: GEUS geological interpretation. Vert. Exag. 10x.