Seismic reflections from depths of less than two meters

Three distinct seismic reflections were obtained from within the upper 2.1 m of flood-plain alluvium in the Arkansas River valley near Great Bend, Kan sas. Reflections were observed at depths of 0.63; 1.46, and 2.10 m and conf irmed by finite-difference wave-equation modeling. The wavefield was densel y sampled by placing geophones at 5-cm intervals, and near-source nonelasti c deformation was minimized by using a very small seismic impulse source. F or the reflections to be visible within this shallow range, low seismic P-w ave velocities (<300 m/s) and high dominant-frequency content of the data ( similar to 450 Hz) were essential. The practical implementation of high-res olution seismic imaging at these depths has the potential to complement gro und-penetrating radar (GPR), chiefly in areas where materials exhibiting hi gh electrical conductivity, such as clays, prevent the effective use of GPR . Potential applications of these results exist in hydrogeology and environ mental, Quaternary, and neotectonic geology.