Valeria Cristina Ferreira Barbosa - Academia.edu (original) (raw)

Uploads

Papers by Valeria Cristina Ferreira Barbosa

15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017

The main goal of Euler deconvolution is to define the source nature and its depth position. Besid... more The main goal of Euler deconvolution is to define the source nature and its depth position. Besides that, it estimates base level of the data and horizontal positions of the sources. To define the correct structural index most authors take advantage of the clustering in depth estimates. Some authors assume constant, linear or nonlinear base levels in their formulation, thus they estimate or eliminate this parameter from their analysis. With a tentative structural index, we take advantage of base level clustering when the correct structural index is used. We modeled three bodies with different structural indices and show that minimum variation of depth is sufficient to indicate the correct structural index when no interfering anomalies are present. In the presence of interfering anomalies, the minimum variation of base level estimates indicates the correct structural index. We simulated constant and nonlinear base levels in our tests. Application to a real data set shows that nonlinear base level is present possibly due to interfering anomalies. These results are valid independent of geomagnetic field incidence.

15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017

Euler deconvolution is a technique based anomaly measurements, its derivatives and structural ind... more Euler deconvolution is a technique based anomaly measurements, its derivatives and structural index. The objective is to estimate the base level of the data, horizontal and vertical positions of the source, usually assuming a tentative structural index. Derivatives are calculated using different techniques and different methodologies exist to indicate the correct structural index. Most of the approaches define the correct depth estimates based on structural index estimated. We modeled anomalies magnetized by vertical and inclined directions, generated by an isolated magnetic monopole and calculated its analytical derivatives in order to show what expect from Euler deconvolution estimates for single sources. We then analyzed estimates over the sourceinfluence area and at the borders. These examples clearly show an outstanding pattern for depth and base level estimates when the correct structural index is used. The estimates at these cases, and only at these cases, are constant over the anomaly position. For these cases, this pattern can clearly identify the correct structural index, related to the nature of the source.

SEG Technical Program Expanded Abstracts 2017

The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural ... more The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural index – SI) and its depth position. To define the correct structural index most authors take advantage of the clustering in depth estimates. With tentative structural indices, we take advantage of base level clustering when the correct SI is used. We modeled three bodies with different structural indices simulating interfering magnetic anomalies; even when we assume a null base level in the data the base level estimated by Euler deconvolution generate a nonlinear pattern. The minimum standard deviation of base level estimates over an area delineated by depth estimates can define the correct SI. Application to a real data set shows a nonlinear pattern of the estimated base level, possibly due to interfering anomalies. Our result may infer that the real body of the study is a plug intrusion.

Geophysical Journal International, 2016

The Python code that produces the results presented here is available under a BSD 3-clause open-s... more The Python code that produces the results presented here is available under a BSD 3-clause open-source license at github.com/pinga-lab/paper-moho-inversion-tesseroids Moho model and data: The Moho depth model for South America and the data used to generate it are available under a Creative Commons Attribution 4.0

Journal of Applied Geophysics, 2016

Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3... more Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3D geometry of ore deposits. This task can be achieved by different gravity-gradient inversion methods, many of which use a voxel-based discretization of the Earth's subsurface. To produce a unique and stable solution, an inversion method introduces particular constraints. One constraining inversion introduces a depth-weighting function in the first-order Tikhonov regularization imposing a smoothing on the density-contrast distributions that are not restricted to near-surface regions. Another gravity-gradient inversion, the method of planting anomalous densities, imposes compactness and sharp boundaries on the density-contrast distributions. We used these two inversion methods to invert the airborne gravity-gradient data over the iron-ore deposit at the southern flank of the Gandarela syncline in Quadrilatero Ferrifero (Brazil). Because these methods differ from each other in the particular constraint used, the estimated 3D density-contrast distributions reveal different geologic features of ore deposit. The depth-weighting smoothing inversion reveals variable dip directions along the strike of the retrieved iron-ore body. The planting anomalous density inversion estimates a compact iron-ore mass with a single density contrast, which reveals a variable volume of the iron ore along its strike increasing towards the hinge zone of the Gandarela syncline which is the zone of maximum compression. The combination of the geologic features inferred from each estimate leads to a synergistic effect, revealing that the iron-ore deposit is strongly controlled by the Gandarela syncline.

73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011

ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast ... more ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast distribution defined on a user-specified grid of prisms. Our method consists of an iterative algorithm that does not require the solution of large equation system. Instead, the solution grows systematically around user-specified prismatic elements called “seeds”. Each seed can have a different density contrast, allowing the interpretation of multiples bodies with different density contrasts. The compactness of the solution is imposed by means of a regularizing function that favors compact bodies closest to the priorly specified seeds. The solution grows by accreting neighboring prisms of the current solution. The prisms for the accretion are chosen by systematically searching the set of current neighboring prisms. Therefore, this approach allows that the columns of the Jacobian matrix be calculated on demand. This is a known technique from computer science called “lazy evaluation”, which greatly reduces the demand of computer memory and processing time. Test on synthetic data from multiple buried sources at different depths and on real data collected over iron deposits located in the Quadrilátero Ferr'ifero, southeastern region of Brazil, confirmed the ability of our method in detecting sharp and compact bodies.

9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, 2005

We have provided supplementary material to our article titled “3-D radial gravity gradient invers... more We have provided supplementary material to our article titled “3-D radial gravity gradient inversion” and whose authors are Vanderlei C. Oliveira Jr, and Valeria C. F. Barbosa. In this material, we presented extra results obtained by inverting the gravity-gradient data from a survey over the Vinton salt dome (Louisiana, USA). In these extra results, we investigate the effect on the results caused by the assumption of uncertainties in the density contrast of the cap rock with the host rocks.

10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007

13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013

Contents of this paper were reviewed by the Technical Committee of the 13 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 13 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.

15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017

The main goal of Euler deconvolution is to define the source nature and its depth position. Besid... more The main goal of Euler deconvolution is to define the source nature and its depth position. Besides that, it estimates base level of the data and horizontal positions of the sources. To define the correct structural index most authors take advantage of the clustering in depth estimates. Some authors assume constant, linear or nonlinear base levels in their formulation, thus they estimate or eliminate this parameter from their analysis. With a tentative structural index, we take advantage of base level clustering when the correct structural index is used. We modeled three bodies with different structural indices and show that minimum variation of depth is sufficient to indicate the correct structural index when no interfering anomalies are present. In the presence of interfering anomalies, the minimum variation of base level estimates indicates the correct structural index. We simulated constant and nonlinear base levels in our tests. Application to a real data set shows that nonlinear base level is present possibly due to interfering anomalies. These results are valid independent of geomagnetic field incidence.

15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017

Euler deconvolution is a technique based anomaly measurements, its derivatives and structural ind... more Euler deconvolution is a technique based anomaly measurements, its derivatives and structural index. The objective is to estimate the base level of the data, horizontal and vertical positions of the source, usually assuming a tentative structural index. Derivatives are calculated using different techniques and different methodologies exist to indicate the correct structural index. Most of the approaches define the correct depth estimates based on structural index estimated. We modeled anomalies magnetized by vertical and inclined directions, generated by an isolated magnetic monopole and calculated its analytical derivatives in order to show what expect from Euler deconvolution estimates for single sources. We then analyzed estimates over the sourceinfluence area and at the borders. These examples clearly show an outstanding pattern for depth and base level estimates when the correct structural index is used. The estimates at these cases, and only at these cases, are constant over the anomaly position. For these cases, this pattern can clearly identify the correct structural index, related to the nature of the source.

SEG Technical Program Expanded Abstracts 2017

The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural ... more The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural index – SI) and its depth position. To define the correct structural index most authors take advantage of the clustering in depth estimates. With tentative structural indices, we take advantage of base level clustering when the correct SI is used. We modeled three bodies with different structural indices simulating interfering magnetic anomalies; even when we assume a null base level in the data the base level estimated by Euler deconvolution generate a nonlinear pattern. The minimum standard deviation of base level estimates over an area delineated by depth estimates can define the correct SI. Application to a real data set shows a nonlinear pattern of the estimated base level, possibly due to interfering anomalies. Our result may infer that the real body of the study is a plug intrusion.

Geophysical Journal International, 2016

The Python code that produces the results presented here is available under a BSD 3-clause open-s... more The Python code that produces the results presented here is available under a BSD 3-clause open-source license at github.com/pinga-lab/paper-moho-inversion-tesseroids Moho model and data: The Moho depth model for South America and the data used to generate it are available under a Creative Commons Attribution 4.0

Journal of Applied Geophysics, 2016

Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3... more Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3D geometry of ore deposits. This task can be achieved by different gravity-gradient inversion methods, many of which use a voxel-based discretization of the Earth's subsurface. To produce a unique and stable solution, an inversion method introduces particular constraints. One constraining inversion introduces a depth-weighting function in the first-order Tikhonov regularization imposing a smoothing on the density-contrast distributions that are not restricted to near-surface regions. Another gravity-gradient inversion, the method of planting anomalous densities, imposes compactness and sharp boundaries on the density-contrast distributions. We used these two inversion methods to invert the airborne gravity-gradient data over the iron-ore deposit at the southern flank of the Gandarela syncline in Quadrilatero Ferrifero (Brazil). Because these methods differ from each other in the particular constraint used, the estimated 3D density-contrast distributions reveal different geologic features of ore deposit. The depth-weighting smoothing inversion reveals variable dip directions along the strike of the retrieved iron-ore body. The planting anomalous density inversion estimates a compact iron-ore mass with a single density contrast, which reveals a variable volume of the iron ore along its strike increasing towards the hinge zone of the Gandarela syncline which is the zone of maximum compression. The combination of the geologic features inferred from each estimate leads to a synergistic effect, revealing that the iron-ore deposit is strongly controlled by the Gandarela syncline.

73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011

ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast ... more ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast distribution defined on a user-specified grid of prisms. Our method consists of an iterative algorithm that does not require the solution of large equation system. Instead, the solution grows systematically around user-specified prismatic elements called “seeds”. Each seed can have a different density contrast, allowing the interpretation of multiples bodies with different density contrasts. The compactness of the solution is imposed by means of a regularizing function that favors compact bodies closest to the priorly specified seeds. The solution grows by accreting neighboring prisms of the current solution. The prisms for the accretion are chosen by systematically searching the set of current neighboring prisms. Therefore, this approach allows that the columns of the Jacobian matrix be calculated on demand. This is a known technique from computer science called “lazy evaluation”, which greatly reduces the demand of computer memory and processing time. Test on synthetic data from multiple buried sources at different depths and on real data collected over iron deposits located in the Quadrilátero Ferr'ifero, southeastern region of Brazil, confirmed the ability of our method in detecting sharp and compact bodies.

9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, 2005

We have provided supplementary material to our article titled “3-D radial gravity gradient invers... more We have provided supplementary material to our article titled “3-D radial gravity gradient inversion” and whose authors are Vanderlei C. Oliveira Jr, and Valeria C. F. Barbosa. In this material, we presented extra results obtained by inverting the gravity-gradient data from a survey over the Vinton salt dome (Louisiana, USA). In these extra results, we investigate the effect on the results caused by the assumption of uncertainties in the density contrast of the cap rock with the host rocks.

10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007

13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013

Contents of this paper were reviewed by the Technical Committee of the 13 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 13 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.