Potential pitfalls of crooked‐line seismic reflection surveys

Abstract

During the last few years, the Geological Survey of Canada has pioneered the application of seismic reflection profiling to mineral exploration, in close collaboration with Canadian mining companies and with the Lithoprobe project (e.g., Spencer et al., 1993; Milkereit et al., 1994). Because of the rugged terrain in crystalline rock environments (Dahle et al., 1985; Spencer et al., 1993), vibroseis seismic surveys are frequently conducted along existing roads, resulting in extremely crooked survey profiles. Crooked profiling geometry, coupled with the complex nature of the geological targets, pose special challenges for seismic data processing and interpretation. Many common‐midpoint seismic processing techniques are based on an implicit assumption of a straight‐line survey and are most effective with uniform fold and even offset distribution within common‐midpoint (CMP) gathers. However, with crooked‐line acquisition the CMP gathers are characterized by variable fold and uneven offset distribution. Based on experience with several seismic data sets from mining camps, I have identified two potential pitfalls that stem from acquisition along crooked profiles: (1) seismic transparent zones; and (2) coherent noise. To address these problems, I have critically re‐examined the basic aspects of the CMP processing techniques and have developed robust strategies for dealing with crooked profiles. In this paper, I present a field data example to demonstrate the artifacts and also discuss solutions to eliminate them. Although developed for seismic prospecting in mining camps, the methods presented here are applicable to seismic data acquired in any environment.