1. For discrete seismic reflectors, the minimum separation so that one can ascertain that more than one interface is involved. The value depends on the criteria for ascertaining. The Rayleigh resolution limit is λ/4, where λ is the dominant wavelength. The Widess limit is λ/8. Compare detectable limit. 2. Horizontal resolution on unmigrated seismic sections is often taken as the width of the first Fresnel zone (q.v.).