Reprocessing of high‐resolution seismic reflection data over groundwater‐bearing glacial deposits near Heby, southeastern Sweden, improved the images of near‐surface structure at this site. Post‐stack time migration and pre‐stack depth migration were tested and compared to determine the improvements on imaging an undulating bedrock surface. The pre‐stack depth migration image displays better continuity of the dipping structures within the glacial sediments and provides a more detailed topography of the bedrock reflector. First‐arrival picks were used to define an initial model for input into tomographic inversion. The tomography result then formed the basis for building the migration velocity model. The final pre‐stack depth migration image shows a strong reflection at around 35 m elevation (about 9 m below the surface) that can be correlated to a thin (0.2 m) hard silt layer. The upper 20 m of overburden is interpreted to consist of clay, and the seismic images show weaker sub‐horizontal reflections within this unit, except for the strong silt reflection, consistent with our modelling results. Below 20 m, sand/gravel sediments are present and overlay the bedrock. Forward modelling based on the pre‐stack depth migration image and subsequent processing shows that pre‐stack depth migration provides a higher resolution image compared with post‐stack time migration. Our study shows that pre‐stack depth migration is preferable to post‐stack time migration even for the shallow near‐surface seismic data acquired at Heby, and that integrating tomography, migration, modelling and geological information provides a better understanding of the structure which these groundwater resources are contained in.

No abstract

No abstract