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- Volume 5, Issue 1, 1987
First Break - Volume 5, Issue 1, 1987
Volume 5, Issue 1, 1987
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Variable density Bouguer processing of gravity data from Herault, France
Authors F. Rimbert, J.C. Erling and J. LakshmananThe Herault permit for oil is located in the south of France in very hilly terrain between Mount Aigoual (1500 m) and the sea at Sete. In the preliminary stage of exploration, it was decided that new Bouguer maps, including a variable density one, and a surface density map should be produced. France is covered by a national gravity map published by BRGM on a scale of 1:80000. It was decided that the original data should be recovered and new data acquired to infill the blanks in order to get stations on an average grid of 1.2 by 1.2 km. The existing data had been acquired along roads with a station spacing of 800 to 1200 m, but the road lines were 3 to 6 km apart. Very detailed mining gravity data were also available from the area around Lodeve. After appropriate sampling of the latter data set, 2041 old stations were retained and 619 new stations were planned (Fig. 1). In most of the permit, the new stations were located along tracks or footpaths over the hills, whereas the old grid was located mainly in the valleys. With 2660 stations in total, the number of stations per 100 km2 varies between 60 and 70, and the largest remaining blanks in very inaccessible areas are about 3 by 3 km in size. The data from these stations were processed using a generalised Nettleton method. After isostatic corrections, structures show up much better on the variabie density Bouguer anomaly map, facilitating interpretation. The surface density map shows the low density of the granites, and the high density of the Permian and Jurassic dolomites.
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The determination of the far-field signature of an interacting array of seismic sources from near-field measurements - results from the Delft Air Gun Experiment
More LessData from the Delft Air Gun Experiment demonstrate the success of a new method to determine the far-field signature of a marine seismie source array from nearfield measurements. The method requires the wavefield of the array to be measured in the near field with hydrophones of known relative sensitivity and in a known geometrical configuration with respect to the monopole source elements within the array. If there are n such source elements, at least n near-field hydrophones are required to determine the wavefield. The results from a North Sea line shot with a tuned airgun array show that the signature deconvolution for the wavelet calculated from these near-field measurements is at least as effective as the signature deconvolution for the measured far-field signature. The same line was shot again with the air guns out of synchronisation by as much as 100 ms; the data from the near-field hydrophones allow a deterministic signature deconvolution to be performed to yield a section very similar to that obtained with the tuned array. Without this signature deconvolution on the detuned data, the recovered section is unacceptable. The full power of the method lies in its ability to specify the whole wavefield for each shot. Thus shot-to-shot variability and source directivity may be taken into account in processing. This power has not been exploited in the results presented here.
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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)