GB967589A - - Google Patents

Abstract

967,589. Seismic surveying. LITTON INDUSTRIES Inc. March 20, 1963 [March 21, 1962], No. 10953/63. Drawings to Specification. Heading H4D. A seismic surveying system utilizes a short spread of closely-spaced detectors (hydrophones or geophones) and a relatively longer spread of relatively widely-spaced detectors, the signals from both spreads being subjected to normal " move-out correction appropriate to the depth of interest and simultaneously recorded. The signals from the former spread produce a detailed profile recording of the terrain being surveyed whilst those from the latter spread, which produce a less detailed profile, give an enhanced indication of multiple reflections by the absence of full " move-out " correction for such reflections due to the velocity of seismic waves being lower in the shallower strata in which the " multiples " occur than in the deeper strata being surveyed. The closely-spaced spread may be wholly within the length of the more widely-spaced spread in which case some of the detectors may be common to both spreads or separate " in-line " spreads may be employed. In the first case the shot-point is near the common centre of both spreads but in the case of the " in-line " arrangement a preferred position is at the end of the cable. The signals from the two spreads may be recorded by the same or by separate recorders (which may be of the photographic type) and more than two spreads may be utilized. The invention is particularly described in connection with marine seismic work but is also applicable to land geophysical work.