Angle-gather time migration

Introduction

Angle-gather migration creates seismic images collected by the reflection angle at the point of reflection. Major advantages of this approach are apparent in the case of prestack depth migration. As shown by Prucha et al. (1999), the ray pattern of angle-gather migration is significantly different from that of the conventional common-offset migration. The difference can be exploited for overcoming illumination difficulties of the conventional depth migration in complex geological areas.

In this paper, we explore the angle-gather concept in the case of prestack time migration. The first goal of this study is educational. Since we can develop the complete mathematical theory of angle-gather time migration analytically, it is much easier to understand the most basic properties of the method in the time migration domain. The second goal is practical. Angle gathers present an attractive tool for post-migration AVO/AVA studies and velocity analysis, and even the most basic time migration approach can find a valuable place in the complete toolbox of seismic imaging.

We start with analyzing the traveltime relations for the basic Kirchhoff implementation of angle-gather time migration. The analysis follows Fowler's general approach to prestack time migration methods (Fowler, 1997). Next, we derive formulas for the amplitude weighting and discuss some frequency-domain approaches to angle gathers. Finally, we present simple synthetic tests of the method and discuss further research directions.

Angle-gather time migration