Shallow seismic reflection does not always work

Shallow seismic reflection has seen widespread use in a variety of environmental, groundwater, and engineering applications over the last 15 years. Seismic reflection, like any other geophysical technique, has reasonably well defined limitations. Besides the well-published resolution limitation, the effectiveness of the technique is strongly dependent, and in many cases controlled, by near-surface conditions. Moisture content, sorting, grain size, organic matter, and consolidation are just a few of the key properties of the near-surface that can dramatically affect the quality of seismic reflection data. In some difficult data areas thoughtful parameter design, high-quality equipment (large dynamic range and small electronic noise), and careful processing can overcome adverse near-surface conditions. Tendencies to suggest that data processing is the key to bringing out reflections on CMP stacks that are not identifiable on shot or CMP gathers leads to overselling the technique and inevitable skepticism by clients and potential clients as to the reliability of shallow seismic reflection. As difficult as it may be for shallow seismic reflection practitioners to admit, shallow seismic reflection simply will not work in some settings and for some targets.