Examples

Figure  contains a simple model consisting of a syncline reflector under an undulating surface. The modeling experiment was done using the algorithm explained in Figure  for a constant velocity and the result is shown in Figure (b). During the modeling, we save a wavefield at the bottom of the topography (Figure (a)). Comparing these two wavefields, we can see the effect of the irregular topography, the wavefield has a big discontinuity at the center and fluctuates on the right half because of the surface topography. Migration was performed using the algorithm shown in Figure  and the results are shown in Figure (d). We can see that the syncline reflector is correctly imaged, but there is background noise. During the migration, we saved a wavefield at the bottom of the topography and it is shown in the Figure (c). This Figure shows artifacts due to inaccuracies in the extrapolation algorithm. The noise comes mainly from the inaccuracies of the modeling and the next section presents an improved scheme which simulates nature more closely.

 

synmdl Figure 5 Synthetic model with a syncline reflector image (lower) under an undulating surface (upper).

 

dataimgtp1
Figure 6 Synthetic examples using the first scheme. (a) : Wave field recorded on the depth level at the bottom of the irregular topography. (b) : Wave field recorded on the irregular surface. (c) : Wave field extrapolated back to the bottom of the topography during the migration. (d) : The subsurface image obtained by the migration from the data in Figure (b).