Azimuthal Effects of Structural Dip and CMP Bin Size on Reflection Travel Times

variations in reflection time in 3D CMP gathers may display properties that appear similar to those expected from HTI anisotropy, but—except for rather extreme situations of structural dip and source-receiver offsets—may be negligible for typical seismic applications in most geologic settings. Further, dip related reflection-time variations associated with positions of CMPs in areal subsurface bins add to the complexities of interpreting travel time for analysis. We start with a back-to-basics examination of simple 2D seismic reflections in a single shot gather and how structural dip affects the geometry of the reflections. We then progress to CMP gathers collected from numerous shots and receivers, and describe the character of reflection hyperbolae in both cases. In particular, we examine the lateral translation of reflection hyperbolae in 2D and 3D shot (field) records, and the symmetry of the reflection hyperbolae in CMP gathers. The transition from 2D to 3D geometry also adds variable source-receiver azimuth as one of the parameters defining the geometry. The geometric effects are considered for shot gathers, single CMP gathers and collections of CMP gathers in areal CMP bins, as well as organized CMP bins associated with 2D stack arrays and 3D hybrid supergathers.