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Analytic signals of gravity gradient tensor and their application to estimate source location
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
2010 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 75, no 6, I59-I74 p.Article in journal (Refereed) Published
Abstract [en]

The analytic signal concept can be applied to gravity gradient tensor data in three dimensions. Within the gravity gradient tensor, the horizontal and vertical derivatives of gravity vector components are Hilbert transform pairs. Three analytic signal functions then are introduced along x-, y-, and z-directions. The amplitude of the first vertical derivative of the analytic signals in x- and y-directions enhances the edges of causative bodies. The directional analytic signals are homogenous and satisfy Euler's homogeneity equation. The application of directional analytic signals to Euler deconvolution on generic models demonstrates their ability to locate causative bodies. One of the advantages of this method is that it allows the automatic identification of the structural index from solving three Euler equations derived from the gravity gradient tensor for a collection of data points in a window. The other advantage is a reduction of interference effects from neighboring sources by differentiation of the directional analytic signals in x-, y-, and z-directions. Application of the method is demonstrated on gravity gradient tensor data in the Vredefort impact structure, South Africa.

Place, publisher, year, edition, pages
2010. Vol. 75, no 6, I59-I74 p.
Keyword [en]
gravity, Hilbert transforms, meteorite craters
National Category
Earth and Related Environmental Sciences
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-142960DOI: 10.1190/1.3493639ISI: 000285767900028OAI: oai:DiVA.org:uu-142960DiVA: diva2:388742
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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