Seismic imaging of steep dips with low fold data: Case studies for Broken Hill and the Lachlan Fold Belt  

Authors / CoAuthors

Jones, L.E.A. | Fomin, T. | Drummond, B.J.

Abstract

In hard rock regions, a large range of stacking velocities is required to correctly stack reflectors of different dips. Typically, horizontal reflectors stack at 6000 m/s, whereas reflectors with dips of 60 degrees stack at 12,000 m/s. For high fold (vibroseis) data, correct stack of conflicting dips can be achieved by dip moveout (DMO) correction. However, for lower fold (dynamite) data, the sparse offset distribution complicates application of DMO. An alternative technique involves producing stacks with different stacking velocities and stacking these stacks. This technique was applied to two data sets, low fold dynamite from Broken Hill, and high fold vibroseis data from the Lachlan Fold Belt. The Lachlan data set was used as both full 60 fold and 10 fold (reduced by selecting every 6th shot). Velocity analysis, both analytical and empirical, was carried out to determine the stacking velocities. Stacking velocity increases with dip angle (cos-1theta), but the velocity range across which an event stacks coherently increases more rapidly (approximately cos-3theta). The most critical area for analysis is the first 2 seconds of data, due to greater sensitivity of NMO to stacking velocity. The optimum number of stacks is an important consideration, based on the number of stacks in which an event contributes coherently to the sum. A range of stacking algorithms was tested, including nth root stacks and coherency weighting. The Broken Hill stack data showed simultaneous imaging of horizontal and dipping events. For the Lachlan reduced fold data, horizontal and moderate to steeply dipping events were stacked successfully. Comparison of these results with the post-DMO stack of the full 60 fold data demonstrates the validity of the technique.

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nonGeographicDataset

eCat Id

40435

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Keywords

• External PublicationAbstract

( Theme )

• seismic sections

( Theme )

• seismology

• AU-NSW

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2003-01-01T00:00:00

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Creative Commons Attribution 4.0 International Licence    

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[-35.0, -30.0, 140.0, 150.0]

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