Authors / CoAuthors
Jones, L.E.A. | Drummond, B.J.
Abstract
Deep seismic reflection profiling of the crust often images structures with dips that are less than those predicted from outcrop scale geology. This is often explained in terms of the seismic process being tuned to sub-horizontal reflectors. However, for typical acquisition parameters in Australian continental studies, steep dips can be imaged in the near surface, and dips up to 40? near the base of normal thickness crust. The key processing steps for imaging steep reflectors at shallow levels are spectral equalisation to suppress near surface noise, fine-tuned statics corrections and detailed stacking (NMO) velocity analysis, including application of dip moveout (DMO). Two effects on stacking velocity must be considered: (1) A high stacking velocity gradient exists at shallow levels due to the low velocity regolith which can exceed 100 m thickness in many parts of Australia and (2) stacking velocity for dipping reflectors equals V/cos theta, theta being the dip. Since normal moveout is most sensitive to stacking velocity at small two-way travel times, it is impossible to simultaneously stack shallow horizontal and steeply dipping reflectors unless DMO or pre-stack migration is applied. In areas of rapidly varying bedrock topography, refraction statics alone may not be sufficient. A useful technique for fine-tuning refraction statics with automatic residual statics involves keying on deeper, more continuous horizons with minimal sensitivity to stacking velocity. A combination of these steps for both the Lachlan Fold Belt and the Yilgarn Craton successfully imaged reflectors dipping up to 60? and extending from 1 to 2 seconds TWT to base of regolith. Since theory and practice confirm that steep dips can be imaged, the dichotomy between seismic results and geological prediction would therefore indicate that outcrop geology is a poor predictor of regional dip, at least at the scale of the seismic wavelength.
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nonGeographicDataset
eCat Id
41576
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Keywords
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- External PublicationConference Paper
- ( Theme )
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- seismic sections
- ( Theme )
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- seismology
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- AU
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2003-01-01T00:00:00
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geoscientificInformation
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[-44.0, -10.0, 114.0, 156.0]
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