2009 Honorary Lecturer, South and East Asia

Seismic prospecting involves interpreting traveltime and amplitude anomalies. While the former can be understood using ray theory, the latter requires appreciation of the wave nature of the seismic propagation. In this context, the concept of Fresnel zones provides a handy, powerful tool–unencumbered by formidable mathematics–for understanding the relation between the lateral size of a subsurface anomaly and observed seismic amplitude. Starting with a brief historical review of wave theory, we  discuss why wavefront propagates only forward, although Huygen’s construction also permits backward wave propagation. Using the concept of Fresnel zones, zero-offset seismic sections from a terminating reflector and a finite circular disk are discussed in detail and limits of vertical and lateral seismic resolution derived heuristically for finite S/N data. The presentation will bring out the importance of Fresnel zones not only in resolution studies but also for the correct determination of minimum migration aperture for optimum imaging.