The three-dimensional refraction trajectories and travel times in seismic broadside refraction shooting across simple steeply dipping or faulted hypothetical structures are determined when the shotpoint is displaced from the axis. No curved surfaces are assumed and the diffractions to be expected from the structural discontinuities are evaluated. An approximate method for correcting arc time measurements taken over the opposite side to that of the shotpoint is investigated while the conversion of times to dip is discussed. Discussion is also given to the differences in the diffraction time curves caused by changing the shotpoint from the up to the down side of a fault and the relationship these curves have with the refraction time curves in both arc and broadside shooting.
The results of these studies indicate the care that should be taken in distinguishing between refracted and diffracted events, and in relating a measured broadside time to a particular point on the refractor. The latter may lead to significant error when simple mid-point depth computations, often resorted to in field work, are employed.