The 3-D seismic interpreter works with a volume of data. Normally this is done by studying some of each of the three orthogonal slices through the volume. This chapter explores the unique contribution of the horizontal section to structural interpretation. The interpreter of structure needs to be able to judge when to use horizontal sections and when to use vertical ones in the course of an overall interpretive project.
Figure 3-1 demonstrates the conceptual relationship between a volume of subsurface rock and a volume of seismic data. Consider the diagram first to represent subsur-face rocks and the gray surface to be a bedding plane. The two visible vertical faces of the rectangular solid show the two dip components of the plane; the horizontal face shows the strike of the plane. Now consider the rectangular solid of Figure 3-1 to be the equivalent volume of seismic data. The gray plane is now a dipping reflection and its intersections with the three orthogonal faces of the solid show the two components of dip and the strike as before. Hence the attitude of a reflection on a horizontal section indicates directly the strike of the reflecting surface. This is the fundamental property of the horizontal section from which all its unique interpretive value derives.