3-D High-Resolution Reflection Seismic Imaging Of Unconsolidated Glacial Sediments

Shallow 3-D reflection seismic techniques have been used to map glacial deposits overlying the<br>Swiss Molasse Basin. A dense distribution of source and receiver positions resulted in a small CMP<br>bin size of 1.5 m x 1.5 m and a high fold >40. Common processing operations such as<br>deconvolution and bandpass filtering successfully enhanced shallow reflections relative to sourcegenerated<br>noise. Erroneous stacking of refracted and guided waves was avoided by careful selection<br>of top mutes. Three-dimensional migration of the stacked data yielded a reliable high-resolution<br>image of the shallow subsurface (cl50 m). Based on borehole information a continuous reflection<br>at 20 to 40 ms (-14 to -35 m) can be correlated with an interface between near-surface lacustrine<br>deposits and underlying glacial tills. A total of five major subsurface units can be distinguished on<br>the basis of their characteristic seismic facies.