5 Results and interpretation

The unmigrated stacked section obtained from the landstreamer data (Figure 5a) is focused on the bedrock reflection. The reflection can be mapped in high resolution and has good lateral continuity. Some areas, especially on the western side of the profile where the main city is located, show a less clear bedrock reflection. The weathering layer thickness appears to be less than 50 m, with the top of the bedrock at most places close to the surface. The bedrock mostly shows a rough surface morphology characterized by steps that could represent fault displacements or partial erosional surfaces (Figure 5a). As the bedrock reflection is relatively shallow there was no attempt to migrate these data (Black et al., 1994).
The first-break traveltime tomography of the wireless data and the landstreamer reflection results show good correspondences, suggesting a good correspondence between the two processing methods. The tomography results show a good-quality image along the whole profile, also close to the main city as the short offsets are better picked than at far offsets on the wireless recorders. As for the landstreamer section, the weathering layer (with a velocity of about 1300 m/s) has a thickness that goes from 10 to 50 m. The bedrock shows a rough surface with clear steps also in the tomography results (Figure 5b).