Translations:Dictionary:Fig W-6/2/en

FIG. W-6. Wavefront methods. (a) Reversed time-distance curves showing both primary and secondary head waves. (b) Arcs of radii (t_n–t)/V₁ about geophone positions (where t_n=arrival time at geophone n) locate wavefront at time t. Symmetry of critical angles shows refractor dip and reconciling the traveltimes locates the refractor. (c) Extension to a second refractor; new arcs are drawn about points where wavefronts impinge on the first refractor to locate the wavefronts in the second layer.