MIGRATION OF SHALLOW SEISMIC-REFLECTION DATA

We present an analysis of migration effects on seismic reflection images of very shallow targets such as those that are common objectives of engineering, groundwater, and environmental investigations. We use an example of seismic reflection data from depths of 5 to 15 m that show negligible effect from migration, despite the apparent steep dip on the seismic section. Our analysis of the question of when to migrate shallow reflection data indicates it is critical to take into account the highly variable near-surface velocities and the vertical exaggeration on the seismic section. A simple set of calculations is developed as well as a flow chart based on the ''migrator's equation'' that can predict whether migration of an arbitrary shallow seismic section is advisable. Because shallow reflection data are often processed on personal computers, unnecessary migration of a large data set can be prohibitively time-consuming and wasteful.