152 Seismic Imaging • velocity analysis by velocity scan to produce a velocity model; • normal move-out (NMO) corrections to flatten the reflected arrivals. Figure 6.4 illustrates the main evolution of field data during the processing sequence. Special attention was focused on the residual section (Figure 6.4-bottom right), which clearly shows high apparent velocity events associated with reflected waves. Figure 6.4 Deconvolution and wave separation for shot point 1 of the 10EST04 profile. Top left: deconvolution by spectrum equalization in the 12–160 Hz frequency bandwidth. Top right: Extraction of direct and refracted waves by SVD filter. Bottom left: Extraction of surface waves (Pseudo Rayleigh waves) by F-K filter. Bottom right: Reflected waves and residual noise. Adapted from Mendes et al. (2014). Chapter 4 contains more information about the processing sequence, which readers should look through to gain further insight into the method. The NMO correction produced a single fold section (Figure 6.5 left). We considered the traditional definition for reflectivity, RZi = (Zi+1 –Zi) / (Zi+1+Zi) where Zi is the acoustic impedance (product of the density by velocity) at cell i and Zi+1 is the acoustic impedance at cell i+1. Nevertheless, density was neglected in our reflectivity
RkJQdWJsaXNoZXIy NjA3NzQ=