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3D modeling of buried valley geology using airborne electromagnetic data

Buried valleys are important hydrogeological features of glaciated terrains. They are often rechargeable groundwater resources, but can remain undetected by traditional hydrogeological mapping or prospecting campaigns. Airborne electromagnetic (AEM) surveys provide high density information
at a regional scale which can be highly effective at mapping buried valleys. Using AEM data for the Spiritwood valley aquifer system in Manitoba, Canada, we develop 3D electrical property and geological models of the buried valley network. The 3D models are derived from voxel-based segmentation of
electrical resistivity obtained via spatially-constrained inversion of two separate helicopter time-domain electromagnetic datasets (AeroTEM and VTEM) collected over the survey area. The electrical resistivity does not provide unequivocal information on subsurface lithology. We utilize a cognitive
procedure to interpret the electrical property model geometry and to simultaneously incorporate supporting information into the assignment of lithology in the 3D geological model. In the case of the Spiritwood, supporting information includes seismic reflection data and borehole records, both of
which constrain valley geometry and lithology at specific sites and along transects. The large-scale AeroTEM survey provides the basis for modeling the regional extent and connectivity of the Spiritwood valley aquifer system, whereas the local-scale VTEM survey provides higher near-surface
resolution and insight into the detailed shallow architecture of individual buried valleys and their fill.

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