Introduction

The use of synthetic models is invaluable in our attempt to better process reflection seismic data Audebert et al. (1994). The obvious benefit of these models is, of course, that they immediately provide the answer to the underlying question: What is under the surface where the survey is being done? Since the answer is known, individual problems can be isolated. Thus, if the project focus is on testing prestack migration and a synthetic model is used, the known velocity function is exactly correct. On the other hand, if the prestack migration algorithm works, then velocity functions can be modified to find how bad the input velocity function can be before the image is severely distorted Biondi (1990); Etgen (1990); van Trier (1990).

In this paper, only the prestack migration algorithm will be analyzed. Specifically, problems encountered with the imaging, and some techniques for solving those problems, will be covered. The model used for this project is complex, and thus provides for many interesting imaging problems. It will be shown that for such a complex setting, simple zero-offset migration techniques are not effective, and that more complex migration techniques which account for lateral velocity variations and depth conversion are necessary for a good image. In addition, the paper will demonstrate that even this sophisticated migration algorithm cannot take care of all imaging problems, and that other techniques need to be used in conjunction with the prestack migration algorithm. Specifically, a technique of changing the input velocity function will be implemented. By changing the input velocity of the salt from P-wave to S-wave, reflections from this wavefield are stacked in the image.