Abstract
Investigation of the difference between the seismic derived velocities and the check-shot and sonic log velocities, to examine what effect the difference might have on the determination of the true velocity distribution was conducted. Since the investigated area is
assumed to be located on a hinge-line, sediments have been deposited in different environments and thus a change in lithology in both vertical and horizontal directions is expected. In such a situation, an assumption of constant velocity would not be valid, since
rapid changes in velocity from one point to another may occur. Therefore, determination of the true velocity functions in the area is an
important task, requiring as much accuracy as possible.
The velocity data available for this analysis consists of borehole velocity survey and sonic log measurements from nine boreholes. The data set also includes seismic reflection velocity measurements from 54 seismic profiles. The first part of the analysis determines interval and average velocities from these data sources. A critical comparison of these different determined velocities has been done. The derived average and interval velocities are finally corrected using the mean average and interval velocity error, in order to compensate for a systematic biasing influence observed from the well ties. Contour plotting of the seismic velocities shows a general
increasing velocity with depth, as expected with normal compaction. Generally, the velocity plots represent a reasonable correlation with the geological expectation of the subsurface structure. The interpretation of the depth and velocities maps for individual seismic sequences, together with all available geological and geophysical data, will lead to a more complete final interpretation in the study area.