Programa de Pós-Graduação em Geofísica - CPGF/IG
URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2355
O Programa de Pós-Graduação em Geofísica da UFPA (CPGF) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA). Foi o segundo no Brasil a formar recursos humanos em Geofísica em nível de pós-graduação stricto sensu. Criado em 1972, funcionou até 1992 junto com os Cursos de Pós-Graduação em Geoquímica e Geologia.
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Item Acesso aberto (Open Access) Exemplo de bom condicionamento inconveniente causado numericamente na inversão gravimétrica para a estimação das densidades de uma camada(Universidade Federal do Pará, 2014) SOARES, William Pareschi; MARTINS, Cristiano Mendel; http://lattes.cnpq.br/8303640454649778A well-conditioned sensitivity matrix can be inconvenient for estimating densities of a layer? We found an example of this inconvenience numerically caused in the gravimetric inversion when the horizontal dimensions of the elementary sources that make up the interpretive model are very small. Amazingly in this case a gravity inversion to obtain the equivalent layer is not effective and does not fit the data. We found that in this case the well-conditioning of the sensitivity matrix occurs simultaneously with low singular values. This feature of the sensitivity matrix leads to severe loss of resolution and leads to biased estimates and very smooth. It happens that part of the resolution would be mathematically possible to be obtained is lost due to this phenomenon numerical computational degradation of the sensitivity matrix . We present a procedure for repayment of the resolution for mapping the density distribution of a layer, which enables new perspectives on gravimetric applications, including environmental studies. We skirted the numerical problem with a semi-heuristic approach which extends the horizontal dimensions of the elementary sources and subsequently corrects the estimates. We obtained with this new procedure in synthetic tests the distribution of the density contrast outlining lateral contacts between regions of different density contrasts, which would only be possible to recover elemental sources larger. We apply this methodology to the dataset of the Thomas Farm landfill site landfill.Item Acesso aberto (Open Access) Procedimentos lineares de inversão gravimétrica para estimar o relevo 3D do embasamento de bacias sedimentares(Universidade Federal do Pará, 2013) RAMOS, Laisse Costa; MARTINS, Cristiano Mendel; http://lattes.cnpq.br/8303640454649778The technological improvement has provided the acquisition of a large volume of geophysical data, which is why the work of interpretation of gravity anomalies and pet relief sedimentary basins increasingly demand innovation in computational and mathematical formulation that allows for such offer. In order to obtain effective and computationally efficient solutions propose two new methods that incorporate linear inversion procedure for the solution of a nonlinear inversion problem. The first proposed method approximates the solution of the nonlinear inversion by linear inversion procedures and applies corrections in iterations from the initial approach, obeyed until the convergence criterion. The second method proposed solution approximates the nonlinear inversion of the linear inversion procedures only on the first iteration, the second iteration from the additional iterations are applied for correction. The investments made in the two new methods and nonlinear inversion, are stabilized by Tikhonov regularization functional first order (smoothness). The observations are modeled by a set of 3D vertical rectangular prisms whose thicknesses are parameters that define discreetly relief estimated at some points. The realization of nonlinear inversion procedure was necessary to validate the estimated basement relief of sedimentary basins produced by the new proposed methods, this validation is given by comparing the results obtained by the procedures of linear inversion with the inversion of nonlinear . We also evaluate the efficiency and effectiveness of the proposed methods and nonlinear inversion from synthetic tests. The proposed methods have proved more efficient than the nonlinear inversion method, since reduced computational time required to recover virtually identical reliefs. As regards efficiency, we conclude that the proposed methods are as effective as the non-linear inversion, since the estimates of the basement relief scale and are equivalent to each other in shape.Item Acesso aberto (Open Access) Transformação de estimativas suaves aplicadas à interpretação de relevos descontínuos do embasamento(Universidade Federal do Pará, 2014-08-21) MOREIRA, Mayra Moura; SANTOS, Darcicléa Ferreira; http://lattes.cnpq.br/5813659873067927We present a method to delineate the basement relief of sedimentary basins composed by vertical faults and horizontal plans. We assume density contrast between the basement and the sediments constant or decrease with depth, and known. The developed method determines the vertical positions for horizontal plans and horizontal positions for vertical faults through an smooth initial solution of the basement relief. We produce this smooth solution through an efficient method which delineates the smooth basement relief. The horizontal positions of two adjacent faults estimates the extension of only one horizontal terrace. Similarly, the vertical position of two adjacent horizontal terraces estimates the extension of the fault between them. The performance of the proposed method is compared with the computational time of two other inversion methods, which stabilize the solution applying the Total Variation functional. The proposed method always produced solutions in less computational time as compared with the computational time required by other methods. Tests on synthetic data contaminated with zero-mean Gaussian pseudorandom noise with a standard deviation of 0.1 mGal show which proposed method produced satisfactory results and estimated basement topographies close to simulated basement topographies. The proposed method was applied to two sets of real Bouguer anomalies: Steptoe Valley (United States) and San Jacinto Graben (United States). The method produced estimated basement topographies presenting high-angle faults in accordance with the available geological information, which the basins above mentioned were formed by extensional tectonics with the consequent formation of structural settings of sedimentary basins conditioned by normal faults.