27 1. Wave propagation with a cross-line spread. In this figure, the horizontal axis represents the in line offset x, consequently the waves appear with a hyperbolic shape on the T-X diagram. a b c d Figure 1.4 Seismic spreads (a), T-X curves (b), In-line shot (c), Cross-line shot (d). Figure 1.5 shows examples of 2D shot points with split-dip spreads (top) and end-on spreads (bottom). For the end-on spread, the 2 shots are obtained with the source located at the 2 extremities of the receiver line. One shot is called a direct shot, the other a reverse shot. Figure 1.6 shows examples of 3D shot points with cross spread, the cross-line offset varying between 0 and 40 m. With a lateral offset of 40 m, reflected events are clearly visible, as indicated on Figure 1.4-d.
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