115 5. Geophysical methods • the thickness H of the weathering zone is defined by the 2500 m/s iso-velocity depth map; • the average velocity V₁ within the weathering zone is calculated from the velocity model in the 0 to H depth interval; • the velocity V₂ of the refractor is derived from the velocity model within a narrow depth window (approximately 3 m) just below the interface at depth H. The application of this methodology to the 3D dataset is illustrated in Figure A.1. (a) (b) (c) (d) Figure A.1. 3D static corrections from 3D tomographic inversion after geostatistical processing. (a) Thickness H of the weathering zone. (b) Average velocity V1 in the weathering zone. (c) Velocity V2 below the weathering zone. (d) 3D static correction map (–H/V1 + H/V2).
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