3-D seismic imaging of complex structures in glacial deposits

A small-scale, shallow-penetration 3-D reflection seismic survey has been carried out over stratified glacial formations to test the method's potential for delineating fine structural details with a reasonable field effort and cost. Recording was carried out with a 96-channel engineering seismograph. Blank shotgun shells were used as the energy source. Field records were obtained with usable reflection energy up to 500 Hz, exploring approximately a 220-m cubical volume. Although special processing was required to attenuate strongly dispersed and scattered surface waves, a stacked data volume of good quality has been assembled. More than 15 reflecting horizons with vertical resolution of about 1.5 m were clearly delineated within the Wisconsin sediments. Results are in good agreement with local outcrops and core information. The identified reflectors (interbeds) within the Late Wisconsin tills are extremely important. These reflectors may provide potential "hydraulic channels" for the movement of surface contaminants through the till into underlying aquifers.