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Discussion papers
https://doi.org/10.5194/se-2019-30
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2019-30
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Feb 2019

Research article | 20 Feb 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

Migration of Reflector Orientation Attributes in Deep Seismic Profiles: Evidence for Decoupling of the Yilgarn Craton Lower Crust

Andrew J. Calvert1 and Michael P. Doublier2,3 Andrew J. Calvert and Michael P. Doublier
  • 1Department of Earth Sciences, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada
  • 2Mineral Systems Branch, Geoscience Australia, Symonston, ACT 2609, Australia
  • 3Centre for Exploration Targeting, School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia

Abstract. Interpretation of deep seismic data is challenging due to the lack of direct geological constraints from drilling and the more limited amount of data available from 2-D profiles in comparison to hydrocarbon exploration surveys. Thus other constraints that can be derived from the seismic data themselves can be of great value. Though the origin of most deep seismic reflections remains ambiguous, an association between seismic reflections and crustal strain, e.g. shear zones, underlies many interpretations. Estimates of the 3D orientation of reflectors may help associate specific reflections, or regions of the crust, with geological structures mapped at the surface whose orientation and tectonic history are known. In the case of crooked 2-D onshore seismic lines, the orientation of reflections can be estimated when the range of azimuths in a common midpoint gather is greater than approximately 20 degrees, but integration of these orientation attributes into an interpretation of migrated seismic data requires that they also be migrated. Here we present a simple approach to the 2-D migration of these orientation attributes that utilises that apparent the dip of reflections on the unmigrated stack, and maps reflector strike, for example, to a short linear segment depending on its original position and a migration velocity. This interpretation approach has been applied to a seismic line shot across the Younami Terrane of the Australian Yilgarn Craton, and indicates that the lower crust behaved differently from the overlying middle crust as the newly assembled crust collapsed during the Late Archean. Some structures related to approximately east-directed shortening are preserved in the middle crust, but the lower crust is characterized by reflectors that suggest N-NNE-oriented ductile flow. Deployment of off-line receivers during seismic acquisition allows the recording of a larger range of source-receiver azimuths, and should produce more reliable future estimates of reflector attributes.

Andrew J. Calvert and Michael P. Doublier
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Andrew J. Calvert and Michael P. Doublier
Andrew J. Calvert and Michael P. Doublier
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Short summary
Deep (> 40 km) seismic reflection surveys are acquired on land along crooked roads. Using the varying azimuth between source and receiver, the true 3-D orientation of crustal structures can be determined. Applying this method to a survey over the ancient Australian Yilgarn Craton reveals that most reflectors in the lower crust exhibit a systematic dip perpendicular to those in the overlying crust, consistent with lateral flow of a weak lower crust in the hotter early Earth 2.7 billion years ago.
Deep ( 40 km) seismic reflection surveys are acquired on land along crooked roads. Using the...
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