Abstract

A new 3D seismic reflection data set has been used to map the shallow subsurface beneath a key region of the Swiss Rhine Valley. Seismic signals generated by a pipegun were recorded with single 30-Hz geophones distributed across a 277.5 × 357.0-m area. The dense distribution of sources and receivers resulted in a binning grid of 2.12 × 2.12 m and an average fold of ∼22. To improve the visibility and continuity of reflections, a novel processing strategy was designed and applied to the acquired data. A combination of regridding and sharing traces in the common midpoint (CMP) domain resulted in increased S/N ratios with only minor loss of resolution. This prestack interpolation method yielded composite CMPs distributed on a 1.5 × 1.5-m binning grid and an increased average fold of ∼44. The composite CMPs were subjected to a combined linear and hyperbolic τ–p processing scheme that led to the effective separation of reflections from source-generated noise. Finally, 3D depth migration of the stacked data produced high-resolution images of the subsurface from ∼15 to ∼130 m depth. On the basis of characteristic seismic facies and information from nearby boreholes, four principal lithological units were identified. At increasing depths they were glaciofluvial sand and gravel, glaciolacustrine clay and silt, morainal deposits, and sandstone basement. These lithological units were separated by three principal reflecting boundaries that were mapped through the data volume using semiautomatic tracking procedures. The deepest boundary defined a trough-shaped basement structure.

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