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Scaling behavior and the effects of heterogeneity on shallow seismic imaging of mineral deposits: a case study from Brunswick No. 6 mining area, Canada
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Geological Survey of Canada, Ottawa, Ontario-Canada.
University of Alberta, Edmonton, Alberta, Canada.
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2013 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, Vol. 90, 1-18 p.Article in journal (Refereed) Published
Abstract [en]

We have studied the scaling behavior of compressional-wave velocity and density logs from an exploration borehole that extends down to about 700 m depth in the Brunswick No. 6 mining area, Bathurst Mining Camp, Canada. Using statistical methods, vertical and horizontal scale lengths of heterogeneity were estimated. Vertical scale length estimates from the velocity, density and calculated acoustic impedance are 14 m, 33 m, and about 20 m, respectively. Although the estimated scale length for the acoustic impedance implies a weak scattering environment, elastic finite difference modeling of seismic wave propagation in 2D heterogeneous media demonstrates that even this weak scattering medium can mask seismic signals from small, but yet economically feasible, massive sulphide deposits. Further analysis of the synthetic seismic data suggests that in the presence of heterogeneity, lenticular-shaped targets may only exhibit incomplete diffraction signals whereby the down-dip tails of these diffractions are mainly visible on the stacked sections. Therefore, identification of orebody generated diffractions is much easier on the unmigrated stacked sections than on migrated stacked sections. The numerical seismic modeling in 2D heterogeneous media indicates that in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), identification of massive sulphide deposits is possible, but their delineation at depth requires detailed velocity modeling and processing algorithms which can handle the anisotropy.

Place, publisher, year, edition, pages
Elsevier, 2013. Vol. 90, 1-18 p.
Keyword [en]
crystalline rock, scattering, heterogeneity, scaling, modeling
National Category
URN: urn:nbn:se:uu:diva-189088DOI: 10.1016/j.jappgeo.2012.12.003ISI: 000316167700001OAI: oai:DiVA.org:uu-189088DiVA: diva2:580613
Available from: 2012-12-23 Created: 2012-12-23 Last updated: 2013-04-22Bibliographically approved
In thesis
1. Seismic investigations in the Brunswick No. 6 area, Canada – Imaging and heterogeneity
Open this publication in new window or tab >>Seismic investigations in the Brunswick No. 6 area, Canada – Imaging and heterogeneity
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Brunswick No. 6 area, which is located in the Bathurst Mining Camp, New Brunswick, Canada, is the focus of this thesis. Almost a decade ago, in order to improve the understanding of the crustal structures and explore for new mineral deposits at depth, three 2D seismic profiles totaling about 30 km and 3D seismic data covering an area of about 38 km2 were acquired from the study area. Petrophysical properties including compressional-wave velocity and density were also measured in two deep boreholes in the area. These data were recovered and reanalyzed, and the improved seismic images interpreted as the main part of this PhD thesis.

A prestack DMO and poststack migration algorithm was considered for processing both 2D and 3D data. Processing of 2D data revealed shallow and deep reflections, which correlate well with surface geology. Steeply-dipping reflections, some of which could host mineral deposits, were imaged down to a depth of 6-7 km. Processing of 3D data showed similar results to the processed 2D profiles. Nevertheless, the non-orthogonal nature of the 3D survey, combined with irregular distribution of offsets, azimuths and trace midpoints, caused a severe acquisition footprint masking reflections in the DMO-corrected unmigrated stacked cube. An FK-dip filter in the wavenumber domain was designed to reduce the effects of the acquisition footprint.

To better understand wave propagation and scattering effects, calculated acoustic impedance log from the available borehole data was used to estimate vertical scale length using a von Karman autocorrelation function. 2D synthetic models representative of heterogeneity in the area were generated accounting for the estimated scale length. Numerical modeling was used to study the scattering effects on the synthetic models, where some predefined targets were superimposed in the provided 2D heterogeneous medium. The effects of variable source frequency, longer horizontal scale length and petrophysical fluctuations of heterogeneous medium were also investigated. The modeling results indicate that, in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), the identification of mineral deposits is possible in the unmigrated stacked sections, but can be challenging in the migrated sections.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 73 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1013
Brunswick No. 6, Mineral deposits, 2D and 3D reflection seismic, Acquisition footprint, Scale length, Heterogeneity, Numerical modeling
National Category
Research subject
Geophysics with specialization in Solid Earth Physics
urn:nbn:se:uu:diva-190479 (URN)978-91-554-8578-8 (ISBN)
Public defence
2013-03-01, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Available from: 2013-02-08 Created: 2013-01-08 Last updated: 2013-04-02

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Cheraghi, SaeidMalehmir, Alireza
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