158 Seismic Imaging Adjacent dispersion images were displayed during picking to follow the lateral evolution of different modes and to avoid mode misidentification. The fundamental mode was clearly identified all along the line, whereas the first higher mode was only partially shown, as seen in Figure 6.10. Figure 6.10 Pseudo-sections of SW phase velocity picked for (a) the fundamental and (b) first higher modes along the line after dispersion stacking, represented as a function of the wavelength λ and the spread mid-point position. From Pasquet and Bodet (2017). A model with vertical velocity variation below each extraction window was assumed, therefore, the initial model chosen for the inversion is a one-dimensional stack of 10 homogeneous elastic layers based on a P-wave velocity model and geological information. A neighborhood algorithm (NA) without lateral constraints performs the inversion of the dispersion curves. The results for Xmid = 30 m and Xmid = 110 m are displayed in Figure 6.11.
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