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- Volume 3, Issue 8, 1985
First Break - Volume 3, Issue 8, 1985
Volume 3, Issue 8, 1985
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Wavelets, well logs and Wiener filters
Authors L.R. Lines and S. TreitelThe deconvolution of source wavelets from seismic traces can provide useful estimates of the earth 's impulse response and thereby aid in geological interpretation. This signal analysis tool has been especially useful in the resolution of thin rock layers and has received widespread application since its development in the 1950s. The deconvolution problem often involves the estimation of a wavelet before removing it by digital filtering. Even in the noiseless case, this task is difficult since the seismic trace can be viewed as the convolution of an unknown wavelet coefficient sequence with an unknown earth impulse response. In cases where multiples have been eliminated, this impulse response becomes transformed into a sequence of reftection coefficients. As pointed out by Ziolkowski (1982), this deconvolution will yield non-unique solutions since it essentially involves solving one equation for two unknown sequences: the wavelet coefficients and the reflection coefficients. However, this inverse problem is not hopeless since the two sequences generally have different statistical properties. Moreover, well log data may be used to sort out the non-uniqueness. The Earth's impulse response derived from well log information and the statistical estimate of the source wavelet can be modified together by least squares inversion in order to model the seismic trace and provide reliable wavelet estimates. Recent wavelet estimation research has shown a similarity between wavelet estimates obtained by least squares inversion and those found by deconvolution of the earth's impulse response from the seismic trace. Upon examination of these procedures, it turns out that least squares inversion with a constrained earth's impulse response is equivalent to deriving the Wiener filter which shapes the earth's impulse response to the recorded seismic trace. When reflection coefficients derived from a well log are simply used as an initial guess for model, parameters, the unconstrained inversion procedure provides wavelet estimates which are similar to wavelet estimates obtained by deconvolution of the earth's impulse response. The similarities are demonstrated for synthetic and real data cases, and explained in heuristic terms.
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On the structural development of the salt dome province in NW Jutland, Denmark, based on seismic studies
More LessAs a result of the renewed interest in Danish salt structures the Geological Survey of Denmark (DGU) engaged the author to outline the structural development of the salt dome province in NW Jutland, which is a part of the Norwegian Danish Basin. The work comprised the interpretation of 79 seismic sections and construction and analysis of 9 two-way time maps, 13 isopach maps and 11 cross-sections (Boldreel 1983, and in preparation). In this article only three two-way time maps, four isopach maps and two cross-sections are diseussed to iIIustrate some of the most important results. Within the area investigated there are seven salt diapirs and one salt pillow. There is a marked correlation between the positions of the stationary salt diapirs and faults in the base of Zechstein, and also between the temporal development of the diapirs and the isopachs of post-Zechstein sediments. The growth of salt pillows started in the Lower Carnian (Upper Triassic). Development of salt diapirs with associated second order peripheral sinks took place asymmetrically without lateral movement of the salt structures. In contrast the one remaining salt pillow, which has not developed diapirically, has moved from its original position in the northern part of the area towards the north-west. The movement of Zechstein deposits is minimal at present thicknesses of 300-600 m and has ceased at present thicknesses of less than 300 m. This leads to the conclusion that the Zechstein sequence does not consist of pure halite.
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A portable seismic computing benchmark
By L. HattonA popular conundrum posed by computational seismologists concerns the performance of various computers on seismic data. Comparing throughputs, i.e. the amount of data which can be processed in some convenient period such as a month or perhaps a British standard business lunchtime, is usually complicated by the use of different seismic software packages, different processing sequences, different data densities, good oldfashioned exaggeration, memory lapses and so on. The only commonly used benchmark to my knowledge is the venerable Whetstone benchmark, designed many years ago to test floating point operations. Unfortunately, this program is very much smaller than typical scientific programs of any kind, let alone seismic programs, and no I/O (input/output) is performed. As a result the Whetstone benchmark is, in my experience, almost useless for testing seismic computer systems.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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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 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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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)