Figure is the result of an industry standard Kirchhoff migration of the Marmousi synthetic using first-arrival traveltimes calculated with a finite-difference eikonal equation solver. The faults and beds in the upper portion are well imaged; however, the anticlinal structure below 2300 m and the target zone at a lateral position of about 6500 m and depth of 2500 m is not imaged.
The migration result corresponds exactly to the observations made in comparing the acoustic wavefield modeling to contours of first-arrival traveltime. The upper 1500 m to 2000 m of the migration which is well imaged corresponds to the wavefields and contours of Figure . In this part of the model, the first-arrival traveltimes accurately parameterize the high energy portion of the wavefield. The left and right sides of the figure are nicely imaged because the velocity model is relatively simple in these areas. The central portion of the image, at the target zone, corresponds to the wavefields and traveltime contours of Figure . The propagation here is complicated by the overlying faults which contain fast and slow velocity regions, and by the high velocity salt which partially overlays the target.
The properties of first-arrival traveltimes described in the preceding section, as well as the observation that Kirchhoff migration using first-arrival traveltimes produces an acceptable image of the upper part of the Marmousi synthetic, motivated the development of the layer-stripping method described next.