88 Geophysics in Geothermal Exploration Figure 2.24 shows the velocity distribution at different depths (15 and 20 m), the 2500 m/s iso-velocity depth map, and a 3D block with vertical velocity sections located at a 0 m, 60 m, and 180 m distance in the crossline direction and velocity map located at 20 m in depth. (a) (b) (c) (d) Figure 2.24 Results of 3D tomography. (a) Velocity distribution at 15 m in depth, (b) velocity distribution at 20 m in depth, (c) 2500 m/s iso velocity depth map, (d) 3D block with vertical velocity sections located at a 0 m, 60 m, and 180 m distance in the crossline direction and velocity map located at 20 m in depth. After Mari and Mendes (2019). Reflection seismic method Seismic reflection is the most widely used seismic technique which has the advantage of providing a picture of the subsurface in two or three dimensions (2D or 3D) in a regular grid (Figure 2.25). 3D data are now increasingly used for field development and production and not only as an exploration tool. Pre-planning of the 3D surveys became then
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