# Translations:The wave equation/9/en

A wavefront also can refer to the leading edge of a waveform. A wavefront chart (Figure 4) is a plot of horizontal distance *x* versus depth z on which wavefronts have been drawn emanating from a source. The wavefronts show the position of a traveling seismic disturbance at successive times. The shapes of the wavefronts depend on the velocity distribution of the rocks. On such charts, raypaths corresponding to different move-outs also can be drawn. These raypaths are perpendicular to the wavefronts for isotropic media. Sometimes, wavefront charts are drawn that are specific for a particular location where velocity varies laterally; in such cases, the wavefront charts are asymmetric. For the case in which velocity varies only with depth, the wavefront chart is symmetric with respect to the vertical raypath.