149 6. Hybrid seismic imaging By taking advantage of multi-shot acquisition setups, a stacked dispersion curve can be obtained. The dispersion curve is a diagram of phase velocity versus frequency. S-wave velocity can be obtained by the inversion of dispersion curves, using a global search method with a neighborhood algorithm (NA). The distribution of both velocities is productively combined to evaluate mechanical properties of the subsurface, which are critical properties for many geotechnical foundation designs, aquifer system characterizations and the time-lapse monitoring of shallow water content. 6.1 Refraction-reflection imaging The main purpose of this example is to obtain a complete shallow subsurface image for the reflectivity property through the simple and fast processing of refraction survey data. The refraction survey was carried out near the underground research laboratory of Andra (National Radioactive Waste Management Agency) located in the eastern region of France. The refraction survey, collected by the geophysical company DMT GmbH & Co KG, aimed to estimate the velocity field in the near surface zone (weathering zone) for a reliable evaluation of static corrections. The intention was to improve the processing of a high-resolution 3D seismic survey of 37 km2, which also covered this region (Figure 6.1). Figure 6.1 Plan view of the 3D seismic reflection survey area (magenta polygon) with the location of three relevant 2D seismic refraction profiles (red points): 10EST04, 10EST09, 10EST06. Adapted from Mendes et al. (2014).
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