Amplitude-offset relationships over shallow velocity inversions

The amplitude and phase of reflected seismic data can vary significantly with the offset distance between source and receiver. Analysis of amplitude-offset relationships in high-resolution seismic data from areas of shallow permafrost in the Beaufort Sea is undertaken in this paper. Reflection attributes produced by energy partitioning at interfaces under nonnormal angles of incidence were studied by means of ray tracing and the Zoeppritz equations. Observed amplitude and phase variations were found to cause CDP stacking techniques to degrade reflection data quality, particularly where the zone of interest features velocity inversions or is shallow in relation to receiver lengths. In these cases velocity analysis based on coherency measures may result in the selection of incorrect stacking velocities.