GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 3.1 589 GEOLOGICAL MODELLING IMPLICATIONS OF DIFFERENT INVERSION STRATEGIES FROM AEM DATA A. Rapiti 1 , F. Jørgensen 2 , A. Menghini 3 , A. Viezzoli 3 , G. Vignoli 4 1 Dept. Of Earth Sciences, Univ. of Pisa, Pisa, Italy 2 Central Denmark Region, Viborg, DK 3 Aarhus Geophysics, Pisa, Italy 4 DICAAR, Univ. of Cagliari, Cagliari, ITA and GRUK, GEUS, Aarhus, DK The purpose of the present study is to show what can be achieved from AEM data by using different inversion approaches and the associated geological modelling implications. Groundwater has been poorly understood in the Peace Region of NE British Columbia (Canada), an area of significant natural gas development. The Peace Project is a collaborative effort aimed at providing baseline information to First Nations communities and government to help make informed groundwater management decisions. The present study is part of The Peace Project designed to locate and map shallow aquifers. The study area is situated in the Peace Region, involving an area of about 1960 km 2 . The dataset consists of approximately 4500 line-km of AEM data (Viezzoli et al. , 2018), located in the North Western part of the Peace River Project (Fig. 1). The geological setting of the area is dominated by its position between the Cordillera Orogenic Belt, to the west, andAlberta Foreland Basin to the east. According to the stratigraphy of the nearby areas (Jørgensen et al. , 2016), the lithostratigraphical formations that are within the expected penetration depths of the SkyTEMmethod (2-400 m) are, from below: the Nordegg Formation composed by calcareous mudstones, the Buckinghorse Formation composed by shales, silty mudstones and siltstones, the Sikanni Formation composed by alternating layers of sandstone and siltstone, the Sully Formations composed of mainly shales and siltstones and the Dunvegan Formation mainly composed by sandstone with subordinate conglomerates (Jørgensen et al. , 2016). Quaternary deposits include different kind of depositional facies. Among these, one can find the resistive glaciofluvial deposits and conductive glaciolacustrine deposits. In 2017, Aarhus Geophysics Aps processed a portion of the EM dataset in the north-west corner of the Peace project area, starting from raw data, adopting state of the art methodologies aimed at reducing artefacts in the data, and therefore in the derived models (Auken et al. , 2009). The geological and hydrogeological interpretations, for the entire dataset in the North Western area, were carried out by GEUS in 2017. Fig. 1 - Right panel: Canada - adapted from www.google.it/maps. Central panel: The green polygon is the Peace Project MainArea - adapted from www.geosciencebc.com . Left panel: The red polygon outlines the area of the dataset located in the N-W part of the Peace River Project. The two solid red lines (A-B) are two cross-sections used for testing different types of regularization. The black polygon (Area1), within the red one, outlines the area involved in the present study. Adapted from Petrel Robertson, 2015