150 Seismic Imaging Several refraction profiles were then implemented with a total spread length of 203 m for each profile. The 10 Hz vertical geophones, 48 in total, were spread with a receiver spacing of 2.5 m for source offsets ranging from 1 to 7.5 m and 5 m for source offsets larger than 7.5 m. The source was a weight dropper (10 kJ) shooting at 3 points: shot point 1 (SP01) with a 1 m offset from geophone 1, shot point 2 (SP02) with a 1 m offset from both geophones 24 and 25, and shot point 3 (SP03) with a 1 m offset from geophone 48. Figure 6.2 shows a diagram of the acquisition spread and the three common shot-gathers of the 10EST04 profile. Figure 6.2 Refraction seismic acquisition: spread and the three-common shot-gathers of the 10EST04 profile. Adapted from Mendes et al. (2014). Full details describing the acquisition and seismic hybrid processing of this field example are presented in Mendes, Mari and Hayet, 2014 (Mendes et al., 2014). This chapter presents only a brief outline. The first step was to derive a depth velocity model for the shallowest region from the processing of first arrivals (direct, diving or refracted waves). The Plus-Minus method of refraction interpretation (Hagedoorn, 1959) using the first-arrival time information was used to produce an interval velocity depth model: the weathered
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