Analysis of isopach maps: Isolation and enhancement of thickness anomalies by digital filtering

Abstract

The isolation of interesting geophysical anomalies by the method of anomaly separation, and the enhancement of latent diagnostic features within the data by calculation of the second vertical derivative, are well-established techniques in the interpretation of gravity and magnetic data as practised in exploration geophysics. The application of these techniques to seismic depth maps was pioneered by Dobrin and Rimmer in 1964. In this paper, the techniques are applied to isopach maps based on seismic reflection data. A demonstration of these techniques shows that the exact locations of local thinning, such as those due to synsedimentary structural growth, or of local thickening, may be determined even in the presence of pronounced regional changes in thickness and in areas where they are not readily apparent on the original maps. The diagnostic value of both methods is illustrated by examples based on data from concession block 9 12 in the Norwegian sector of the North Sea. These examples refer to local thinning of stratigraphic intervals overlying salt plugs at depth. It is pointed out that the methods are equally applicable to other exploration situations where the isolation and enhancement of variations in stratigraphic thickness is important.