Special Issue Shallow seismic reflection section—Introduction

For those interested in shallow seismic reflection (SSR) techniques, this special issue of G E O P H Y S I C S is likely to serve as a useful reference for years to come. The idea for this issue grew out of discussions that took place at the Shallow Seismic Reflection Workshop at the Lawrence Berkeley Laboratory, California, in September 1996. The content of those discussions is the subject of a published report elsewhere (Steeples et al., 1997). Several workshop participants and their colleagues contributed to the papers in this issue as authors and as reviewers. The articles include case histories, novel uses of the SSR technique, state-of-the-art planning considerations for 3-D SSR surveys, and some examples of problems unique to SSR surveying. With regard to SSR surveys as compared to those undertaken at greater depths, the physics of the earth remains constant; however, the relative importance of various aspects of the physics varies significantly between the two. For example, frequency filtering often can remove low-frequency surface waves from high-frequency SSR data, but this is not necessarily the case for reflection data gathered at greater depths. Conversely, removing shallow refractions from SSR data is a problem rarely encountered in deeper surveys. The modern use of SSR methods can be said to have begun with Schepers (1975), who produced some excellent shallow P-wave reflection results in Germany that were not appreciated fully in North America until the 1980s. Even earlier, Evison (1952) had contemplated the problems and frustrations involved in detecting seismic reflections in the shallow zone. Work by Pakiser and his colleagues at the U.S. Geological Survey appears to be the first published example of the successful use of seismic reflection at depths shallower than 50 m (Pakiser and Mabey, 1954; Pakiser et al., 1954; Pakiser and Warrick, 1956; Warrick and Winslow, 1960). This effort was abandoned because of the high cost of the surveys and because, in the absence of digital processing, the technique did not work well in many of the locations surveyed. In addition, Pakiser and his colleagues were called upon to implement a major program analyzing deep crustal structure to help detect underground nuclear explosions and to discriminate them from earthquakes,