# Dictionary:Raypath

A line everywhere perpendicular to wavefronts (in isotropic media). A raypath is characterized by its direction at the surface, often expressed as stepout:

where =angle with vertical, *V*=instantaneous velocity, and *p*=*raypath parameter* (q.v.). While seismic energy does not travel only along raypaths (i.e., seismic energy would reach points by diffraction even if the raypath were blocked), raypaths constitute a useful method of determining arrival time by ray tracing. Note that raypath bending depends on changes in velocity, not changes in acoustic impedance. Raypaths are usually shown on wavefront charts; see Figure W-3.