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Interpretation of aeromagnetic data using eigenvector analysis of pseudogravity gradient tensor
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.
(Formerly Geological Survey of Iran, Division of Airborne Geophysics)
2011 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 76, no 3, L1-L10 p.Article in journal (Refereed) Published
Abstract [en]

This study has shown that the same properties of the gravity gradient tensor are valid for the pseudogravity gradient tensor derived from magnetic field data, assuming that the magnetization direction is known. Eigenvectors of the pseudogravity gradient tensor are used to estimate depth to the center of mass of geologic bodies. The strike directions of 2D geological structures are estimated from the eigenvectors corresponding to the smallest eigenvalues. For a set of data points enclosed by a square window, a robust least-squares procedure is used to estimate the source point which has the smallest sum of squared distances tothe lines passing through the measurement points and parallel to the eigenvectors corresponding to the maximum eigenvalues. The dimensionality of the pseudogravity field is defined from the dimensionality indicator I, derived from the tensor components. In the case of quasi-2D sources, a rectangular window is used in the robust leastsquares procedure to reduce the uncertainty of estimations. Based on synthetic data sets, the method was tested on synthetic models and found to be robust to random noise in magnetic field data. The application of the method was also tested on a pseudogravity gradient tensor derived from total magnetic field data over the Särna area in west-central Sweden. Combined with Euler deconvolution, the method provides useful complementary information for interpretation of aeromagnetic data.

Place, publisher, year, edition, pages
USA: SEG , 2011. Vol. 76, no 3, L1-L10 p.
National Category
Physical Sciences
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-142951DOI: 10.1190/1.3555343ISI: 000293522500024OAI: oai:DiVA.org:uu-142951DiVA: diva2:388727
Available from: 2011-01-18 Created: 2011-01-18 Last updated: 2017-12-11Bibliographically approved
In thesis
1. New Techniques for Estimation of Source Parameters: Applications to Airborne Gravity and Pseudo-Gravity Gradient Tensors
Open this publication in new window or tab >>New Techniques for Estimation of Source Parameters: Applications to Airborne Gravity and Pseudo-Gravity Gradient Tensors
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gravity gradient tensor (GGT) data contains the second derivatives of the Earth’s gravitational potential in three orthogonal directions. GGT data can be measured either using land, airborne, marine or space platforms. In the last two decades, the applications of GGT data in hydrocarbon exploration, mineral exploration and structural geology have increased considerably.

This work focuses on developing new interpretation techniques for GGT data as well as pseudo-gravity gradient tensor (PGGT) derived from measured magnetic field. The applications of developed methods are demonstrated on a GGT data set from the Vredefort impact structure, South Africa and a magnetic data set from the Särna area, west central Sweden.

The eigenvectors of the symmetric GGT can be used to estimate the position of the causative body as well as its strike direction. For a given measurement point, the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the source body. For quasi 2D structures, the strike direction of the source can be estimated from the direction of the eigenvectors corresponding to the smallest eigenvalues. The same properties of GGT are valid for the pseudo-gravity gradient tensor (PGGT) derived from magnetic field data assuming that the magnetization direction is known.

The analytic signal concept is applied to GGT data in three dimensions. Three analytic signal functions are introduced along x-, y- and z-directions which are called directional analytic signals. The directional analytic signals are homogenous and satisfy Euler’s homogeneity equation. Euler deconvolution of directional analytic signals can be used to locate causative bodies. The structural index of the gravity field is automatically identified from solving three Euler equations derived from the GGT for a set of data points located within a square window with adjustable size.

For 2D causative bodies with geometry striking in the y-direction, the measured gxz and gzz components of GGT can be jointly inverted for estimating the parameters of infinite dike and geological contact models. Once the strike direction of 2D causative body is estimated, the measured components can be transformed into the strike coordinate system. The GGT data within a set of square windows for both infinite dike and geological contact models are deconvolved and the best model is chosen based on the smallest data fit error.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 800
Keyword
Gravity gradient tensor, pseudo-gravity, magnetic field, eigenvector analysis, least squares algorithm, strike direction, source parameter estimation, analytic signal, Euler deconvolution, joint inversion, infinite dike model, geological contact model
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-143015 (URN)978-91-554-7986-2 (ISBN)
Public defence
2011-03-04, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 730Available from: 2011-02-09 Created: 2011-01-18 Last updated: 2011-03-21Bibliographically approved

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