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Bedrock mapping of buried valley networks using seismic reflection and airborne electromagnetic data

In glaciated terrain, buried valleys often host aquifers that are significant groundwater resources. However, given the multitude of scales and spatial complexity, buried valleys often remain undetected or insufficiently mapped. Accurate and thorough mapping of bedrock topography is a
crucial step in detecting and delineating buried valleys and understanding process formation. We develop a 3D bedrock mapping procedure supported by the combination of seismic reflection data and helicopter time-domain electromagnetic data with water well records for the Spiritwood buried valley
aquifer system in Manitoba, Canada. The limited spatial density of water well bedrock observations precludes complete depiction of the buried valley bedrock topography and renders the water well records alone inadequate for accurate hydrogeological model building. Instead, we leverage the
complementary strengths of seismic reflection and airborne electromagnetic data for accurate local detection of the sediment-bedrock interface and for spatially extensive coverage, respectively. Seismic reflection data are used to define buried valley morphology in cross-section beneath 2D survey
lines distributed over a regional area. The 3D model of electrical conductivity derived from inversion of the airborne electromagnetic data is then used to propagate buried valley morphology over the entire survey area. Propagation is performed using a spatially-variable assignment of the electrical
conductivity at the sediment-bedrock interface for different parts of the valley morphology identified in the seismic cross-sections. The 3D locus of points defining each morphological valley feature is constructed using a path optimization routine between seismic survey lines that utilizes
deviation from the assigned electrical conductivities as the cost function. Our resulting map represents a bedrock surface of unprecedented detail with more complexity than has been suggested by previous investigations. Our procedure is largely data-driven with an adaptable degree of expert user
input that provides a clear protocol for incorporating different types of geophysical data into the 3D bedrock mapping procedure.









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