FRESNEL ZONES IN THE LIGHT OF BROAD-BAND DATA

The investigation of zero-offset response to circular reflectors of increasing Fresnel zone size shows that reflection response is a constant and is independent of reflector size, except when the reflector diameter is so small that the diffractions interfere with the primary reflection. The extent of this effect is dependent upon vertical resolution and the time separation of the primary reflector and the diffraction. Interference occurs for reflectors smaller in diameter than the first Fresnel zone. Migration removes this interference. For broadband data the Fresnel zone solution breaks into two parts: the primary reflector and the edge-effects diffractor. With broadband seismic data, reflections and diffractions separate in time, except at locations near faults or very small bodies. Reflections are the seismic response to interlayer discontinuity and are independent of reflector size. Diffractions are the seismic response to lateral discontinuities and edges and depend on proximity to-and geometry of-the edge. Except in the locale of an edge, broadband reflections and diffractions are separated physically on the section and mentally by the interpreter. Furthermore, standard CMP processing attenuates diffractions, especially when CMP lateral offset is some distance from the diffractor.