93 2. Surface geophysical methods Figure 2.28 Example of a 3D shot point. You can see the refracted wave, the reflected wave, the air wave, and the surface wave. The air wave is aliased. After Mari and Mendes (2019). The processing sequence of each shot includes amplitude recovery, deconvolution in the 15–150 Hz frequency bandwidth, tail mute, static corrections computed with the GRM method. The deconvolution is done to increase the resolution and attenuate the surface waves. A tail mute is used to kill the air waves and the surface waves. The static corrections are done to compensate the effects of the weathering zone. In the example, the 3D static corrections are very weak. The data are sorted in Common Mid-Point gathers (CMP). Normal Move Out (NMO) corrections are done with a stacking velocity model obtained by velocity analysis. Surface consistent residual statics are computed to enhance the signal to noise ratio and preserve the high resolution of the data in the CMP stack procedure. The 3D block is composed of 13 in-line sections 1 m apart. Each section is composed of 44 CMP points 1 m apart. Figure 2.29 shows an example of in-line and crossline seismic sections extracted from the 3D block. The two sections presented (section 6 in the in-line direction, and section 23 in the crossline direction) intersect in the middle of the 3D block. They have been filtered in the 15-100 Hz bandwidth, which provides an excellent signal-to-noise ratio.
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