Converted wave prestack migration in the presence of topography: synthetic cases

Saúl Ernesto Guevara, Gary F. Margrave

Converted waves can provide valuable structural and stratigraphic information, which requires suitable processing methods such as prestack migration. Rough topography, present at many places of interest, can reduce the quality of the resulting images. A method of Kirchhoff prestack migration for converted waves in the presence of topography is presented here. A prestack depth migration code for shot gather data was used. Two different synthetic datasets, containing shot gathers with topography over different subsurface structures, were created using an elastic 2D finite-difference method. An eikonal ray-tracing code was used to create the time tables for P and S waves, and the resulting images are presented in time and depth versions. Depth images resemble accurately the geologic model in depth. However, they also appear to have a number of artifacts, mostly related to other wave modes present in the record, and also related to the migration process.

Future work includes more extended applications of these methods, and increasing the accuracy by taking into account issues such as anisotropy and true amplitude.