Evaluation of seismic image quality — Part II: Assessment of velocity models

If we assume that the correct migration algorithm has been used (see part I), errors in seismic images may still be present due to errors in the underlying velocity model. The standard way of detecting velocity errors is to search for misalignments in image gathers. However, the low signal-to-noise ratio of image gathers may make the analysis difficult. Image gathers from CFP gathers have the significant advantage that each member trace involves the contribution of many Fresnel zones and therefore has a relatively high signal content.