Classical processing of 2.5D land seismic surveys has shown to yield unsatisfactory images, even though shot gathers show clear reflections and a good signal to noise ratio. If some major interfaces are easily identified within the stack volume, their 3D geometry remains difficult to appreciate because of a lack of continuity in the cross-receiver line direction. The theoretical aspects of an alternate method allowing a construction of these 3D structures are presented here. This method geometrically migrates picked reflection traveltimes on good quality shot gathers without amplitude or frequency considerations. It is tested on a synthetic dataset from a 3D smoothly deformed reflector that is well recovered by the technique and applied to major reflections of a 2.5D seismic survey, allowing a successful reconstruction of the reflectors. ¿ 1997 American Geophysical Union