Ultra‐shallow seismic imaging of the top of the saturated zone

Abstract

We collected ultra‐shallow seismic‐reflection data to image the near‐surface stratigraphy of a Kansas River point bar. We were successful in identifying a discontinuous clay layer and the top of the saturated zone at depths of 0.95 and 1.4 m. Seismic walkaway data collected using various .22‐caliber ammunition show that decreased source energy is necessary to generate higher frequencies and prevent clipping of critical near‐offset traces needed to identify ultra‐shallow reflections. The seismic reflections exhibited average normal moveout velocities of 180–195 m/s with dominant frequencies of 200–450 Hz. Coincident subsurface features were also imaged using 200‐MHz ground‐penetrating radar. This study presents the shallowest seismic reflection from the top of the saturated zone reported in the literature to date and further demonstrates the potential of using seismic‐reflection methods for ultra‐shallow imaging of the subsurface as a stand‐alone tool or in conjunction with other high‐resolution geophysical techniques.