For 2-D seismic data, the [[prestack trace]]s are sorted into groups associated with one midpoint on the earth's surface. The 3-D seismic data are sorted into discrete areas called bins. All actual midpoints that fall into the bin area belong to that bin. In effect, a grid is laid over the actual midpoints. Each bin has an in-line and cross-line dimension. The [[fold]] of each bin is the number of traces captured by that bin. Through the [[Basic seismic processing#Common midpoint (CMP) stack|stacking]] process, all traces within a bin are summed to create a single stack trace, greatly improving signal quality. | For 2-D seismic data, the [[prestack trace]]s are sorted into groups associated with one midpoint on the earth's surface. The 3-D seismic data are sorted into discrete areas called bins. All actual midpoints that fall into the bin area belong to that bin. In effect, a grid is laid over the actual midpoints. Each bin has an in-line and cross-line dimension. The [[fold]] of each bin is the number of traces captured by that bin. Through the [[Basic seismic processing#Common midpoint (CMP) stack|stacking]] process, all traces within a bin are summed to create a single stack trace, greatly improving signal quality. |