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- Volume 4, Issue 11, 1986
First Break - Volume 4, Issue 11, 1986
Volume 4, Issue 11, 1986
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Calculation of pre-Zechstein Bouguer anomaly in northwest Germany
By H.J. HermesThe gravitational influence of the sedimentary sequence from the surface to the base of the Zechstein (Late Permian) in northwest Germany has been calculated. The structure of the sedimentary sequence is known from interpretation of seismic reflection data. Corrections were ca1culated by taking the differences between the densities of the sedimentary rocks and an assumed density of 2.65 g cm-3 for the pre-Zechstein. Thus a new map showing an improved Bouguer anomaly was obtained, which must essentially depend upon the density distribution below the Zechstein formation. There are several uncertainties: limited data on the densities of the geological formations: deep Tertiary troughs; large Keuper (Upper Triassic) thicknesses; salt domes derived from the Zechstein; and Rotliegendes (Early Permian) troughs in which the base of the Zechstein is at depths of about 10 km. These all cause problems in the determination of the corresponding influences on the gravity. The map of the improved Bouguer anomaly was produced by forward modelling which involved variation of the density values.
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Dereverberation by an adaptive lattice filter
Authors A. Vesnaver and S. PersogliaThe commonly used non-adaptive deconvolution methods (e.g. predictive, homomorphic, frequency domain) are all variations on the same idea. In different ways they derive from the spectrum of the seismic trace an estimate of the basic wavelet. This wavelet is then compressed to improve the resolution and to reduce the reverberations. However, this type of wavelet estimation is statistical, and this is, at the same time, both its strength and its weakness. We know that the greater the statistical weight, the better is the estimate of the seismic wavelet, particularly when the signal-to-noise ratio is poor. On the other hand, if the wavelet is estimated from an excessive amount of data it becomes difficult to follow the variations in space and time of the seismic signal. This limitation is one of the reasons for the study of adaptive and time-varying deconvolution methods. Among the various adaptive techniques (e.g. Widrow's, Kalman's), that which involves lattice filters attempts most faithfully, from a physical point of view, to reproduce and eliminate the short period reverberations in the uppermost layers and the intrabed multipies. These reverberations, together with the waveform induced by the source, the receiver response and the absorption, tend to broaden the wavelet and so reduce the resolution.
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)