Dissertações em Geofísica (Mestrado) - CPGF/IG
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/4993
O Mestrado Acadêmico pertente a o Programa de Pós-Graduação em Geofísica (CPGF) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).
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Item Acesso aberto (Open Access) Desenvolvimento de técnicas de filtragem e sua aplicação a dados aeromagnéticos da Bacia Amazônica(Universidade Federal do Pará, 1976-08) SILVA, João Batista Corrêa da; LOURENÇO, José SeixasIn this thesis two filtering methods were combined in order to enhance some features in an aeromagnetic map such as lineaments and anomalies caused by sources of large proportions. The visual filtering consisted of stereoscopic examination of pairs of maps. The numeric filtering involved the elimination of the undesirable spectral components (noise) and the enhancement of the desired spectral components (signal). Both methods were tested on aeromagnetic maps of the Middle Amazon Basin. All the numeric filtering operations were done in the space domain by convolving the aeromagnetic data with a 13x13 filter matrix. Special attention was paid to the preliminary analysis of the spectrum, as a guide in filter design. The results of the application of each filter was discussed in detail. A further topic also dealt with was basement fault models. The model analysis established a complementary interpretation method to the filtering methods. A structural interpretation of the Middle Amazon Basin's basement was provided. The dominant aeromagnetic trends were E-W, N60°W, N-S, N45°E and N60°E. Two grabens were quite evident. The younger one trends N-S, while the older one strikes N45°E. Two anomalies caused by sources of intermediate and large proportions (15-60km) exhibit remanent magnetization and high values of negative inclination, which shows that the Amazon Basin would be southernmost in the Paleozoic. In performing the integration of aeromagnetic data with other geophysical data avaiIable, the interpretation from other data proved consistent with the aeromagnetic interpretation, illustrating the reliability of the techniques employed in this thesis.Item Acesso aberto (Open Access) Interpretação quantitativa de anomalias gravimétricas ar-livre da margem continental norte brasileira, setor nordeste(Universidade Federal do Pará, 1990-10-12) CASTRO, David Lopes de; BISCHOFF, Jürgen H.Free-air gravity anomalies across continental margins of passive type present a general standard form. This form can be well explained by a distribution of simple horizontal two-dimensional discontinuities. An automatic process of random search was proposed for quantitative interpretation of the data. Using the method of flexible polyhedron (Simplex), the main parameters of the model were estimated, considering a convenient ration between number of points/number of parameters to be determined. The free-air gravity anomalies over the region of the continental slope can be explained by a single horizontal discontinuity (simple step) and, as the wavenumber domain has information about this anomaly, it was also proposed an iterative graphic procedure for the analysis of the amplitude spectral response for the anomalies. Applying the Fourier transform, it would possible to determine the depth and the off-set of this discontinuity, and, once these parameters are measured, the density is calculated. The basic aim for studying these procedures was to combine the two methods of interpretation in the space and wavenumber domains, in order to obtain a more constrained solution to the geological structure of the studied area. The two interpretative procedures discussed above were applied and their respective capacity of resolution were analysed, over the free-air gravity anomalies of profiles across the continental margin of northeast Brazil, covering the states of Maranhão to Rio Grande do Norte. The survey, called Project EQUANT I, LEG 1, was carried out during the period of August 27 to October 10, 1987, by the Oregon State University (OSU) using the oceanographic ship Prof. W. Besnard of the Oceanographic Institute of São Paulo University (USP). It was demostrated that the inversion done directly in the space domain is more favorable for the interpretation, even for typical anomalies, although the treatment in the spectral domain is relatively simpler.Item Acesso aberto (Open Access) Inversão gravimétrica do relevo de bacias extencionais através da variação total(Universidade Federal do Pará, 2009) LIMA, Williams Almeida; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491We present a gravity inversion method to reconstruct the discontinuous basement relief of a sedimentary basin, whose density contrast between the basement and the sediments is constant, or decreases monotonically with depth, and known. The solution is stabilized using the total variation functional (VT), which does not impose smoothness on the solution. We compare the proposed method with the global smoothness (SG), weighted smoothness (SP) and entropic regularization (RE) methods using synthetic data produced by 2D and 3D basins presenting discontinuous relief. The solutions obtained with the proposed method were better than those obtained with SG and similar to the ones produced by SP and RE. Differently from SP, however, the proposed method does not require a priori knowledge about the basin maximum depth. As compared with RE, the present method is operationally simpler and requires the specification of just one regularization parameter. The VT, SG, and SP methods were also applied to the following areas: Ponte do Poema (UFPA), Steptoe Valley (Nevada, United States), San Jacinto Graben (California, United States) and Büyük Menderes (Turkey). Almost all those areas are characterized by the presence of highangle faults. In all cases, the VT produced basement relief estimates presenting sharp, high-angle discontinuities, in accordance with the tectonic setting of the areas.Item Acesso aberto (Open Access) Inversão gravimétrica do relevo do embasamento usando regularização entrópica(Universidade Federal do Pará, 2007) OLIVEIRA, Alexandre de Souza; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491We present a new gravity inversion method, which estimates the basement relief of a sedimentary basin, whose sediments may present a constant or a decreasing density contrast with depth relative to the basement. The method combines the minimization of the first-order entropy measure with the maximization of the zeroth-order entropy measure of the solution vector (depths to the basement). The interpretation model consists of a set of rectangular juxtaposed vertical prisms with known density contrasts and whose thicknesses represent the depths to the basement relief and are the parameters to be estimated. The minimization of the first-order entropy favors solutions presenting abrupt discontinuities, and the maximization of the zeroth-order entropy is employed just to prevent its excessive minimization. We applied our method to synthetic data simulating: (i) intracratonic basins with smooth or discontinuous relief, and (ii) faulted marginal basins. In the case of a smooth basement relief, it was well delineated by the entropic regularization, and by the global and weighted smoothness. In the case of a faulted basement, either in intracratonic or marginal basins, the entropic regularization and the weighted smoothness delineated the basement relief with good precision, differently from the global smoothness. The entropic regularization, however, did not require the knowledge of the basin’s maximum depth. We applied our method to four sets of real Bouguer anomalies. The first one comes from a profile across a bridge located in the campus of the Federal University of Pará, Belém. The solution delineated the known, discontinuous topography below the bridge. The second set comes from the northern portion of Steptoe Valley, Nevada. The solution delineated a discontinuous basement relief in accordance with the known geological setting of the area. The third set comes from the San Jacinto graben, situated in California, United States. The solution indicated an asymmetric graben, as already reported by other authors. The fourth data set comes from the Büyük Menderes graben, western Turkey. The solutions presented large vertical displacements on the northern border, which is confirmed by geological information.Item Acesso aberto (Open Access) Inversão gravimétrica estável do relevo da base e da variação da densidade com a profundidade em aterros sanitários(Universidade Federal do Pará, 2003-10-21) TEIXEIRA, Wlamir Abreu; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491The present method assumes a decrease in the density contrast of a sedimentary basin according to a hyperbolic law in a waste landfill and uses two approaches: (1) the estimation of the bottom of a waste landfill assuming that the gravity anomaly, the density contrast at the surface and the decaying factor of the density contrast with depth are known; (2) the estimation of the density contrast at the surface and of the decaying factor of the density contrast with depth, assuming that the gravity anomaly and the relief of the waste landfill bottom are known. A variation of the latter approach consists in using the known depth values to the landfill bottom to produce a fitted gravity anomaly and estimate the density contrast at the surface and the decaying factor of the density contrast with depth via minimization of the Euclidean norm of the residual vector between the observed and fitted anomalies. In both cases the interpretation model is a set of vertical rectangular 2D prisms whose thicknesses are parameters to be estimated and represent the depth to the interface separating sediments and basement. The solutions of both problems are stable because of the incorporation of additional a priori information about the smoothness of the estimated relief. The presented method was applied to synthetic data produced by simulated waste landfills having maximum depth to the bottom smaller than 15 m and presenting smooth relief. The results were consistent and demonstrated the effectiveness of the method in both approaches. The method was also applied to the residual Bouguer anomaly from the Thomas Farm, Indiana, USA, leading to the conclusion that the density contrast of the landfill is either constant or present a maximum variation of about 0.09 g/cm3.Item Acesso aberto (Open Access) Inversão gravimétrica estável do relevo do embasamento e da variação da densidade com a profundidade em bacias sedimentares(Universidade Federal do Pará, 2003-10-21) COSTA, Denis Carlos Lima; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491The present method assumes a decrease in the density contrast of a sedimentary basin according to a hyperbolic law and has two objectives: (1) to estimate the basement relief of the sedimentary basin assuming that the gravity anomaly, the density contrast at the surface and the decaying factor of the density contrast with depth are known; (2) to estimate the basement relief, the density contrast at the surface and the decaying factor of the density contrast with depth, assuming that the gravity anomaly and the depth to the basement at a few points are known. In both cases the interpretation model is a set of vertical rectangular 2D prisms whose thicknesses are parameters to be estimated and represent the depth to the interface separating sediments and basement. The solutions of both problems are stable because of the incorporation of additional a priori information about the smoothness of the estimated relief and about the depth to the basement at a few locations, presumably provided by boreholes. The method was tested with synthetic gravity anomalies produced by simulated sedimentary basins presenting smooth relief. The results showed well-resolved estimated relieves. Besides, estimated density contrasts at the surface and the decaying factors of the density contrast with depth close to the true ones were obtained, indicating the potentiality of the proposed method in gravity interpretations of sedimentary basins. The method was applied to the Bouguer anomaly from Recôncavo Basin, producing an estimated relief with a maximum depth of 6 km, a figure similar to the one obtained from seismic interpretations. The estimates of the surface density contrast and of the decaying factor of the density contrast with depth were -0.30 g/cm3 and 30 km, respectively, producing an estimate of 4% for the maximum sediment compaction.Item Acesso aberto (Open Access) Inversão gravimétrica rápida do relevo do embasamento aplicando o funcional da variação total(Universidade Federal do Pará, 2013-08-23) SANTOS, Raphael Di Carlo Silva dos; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491; SANTOS, Darcicléa Ferreira; http://lattes.cnpq.br/5813659873067927We present a new 2D linear inversion gravity method to estimate the discontinuous basement relief of a sedimentary basin. The method uses an interpretation model consisting of a set of 2D juxtaposed horizontal ribbons whose thicknesses are the parameters to be estimated. The density contrast between the basement and the sediments is assumed constant and known. The estimates of the thicknesses were stabilized with the Total Variation functional (TV) which permits solutions presenting local discontinuities in the basement relief. The estimates of the basement relief are produced by solving a single linear system of equations in the L1 norm. Because linear inversion methods underestimate the depth of the basement relief for sedimentary basins thicker than 500 m, we amplify the depth estimates through by modifying the matrix associated with the interpretation model. This procedure in general leads to overestimated depths which are corrected through the expression of the anomaly of a Bouguer slab. Tests on synthetic and real data produced similar results as compared with the nonlinear method, but required less computational time. The ratio R between the computational times required by the nonlinear and the proposed methods to produce similar solutions increases with the number of observations and parameters. For example, for 60 observations and 60 parameters R is equal to 4 whereas for 2500 observations and 2500 R increases to 16.8. The proposed method and the nonlinear inversion method were also applied to real gravity data from Steptoe Valley, Nevada, U.S.A. and from Ponte do POEMA at the Campus of Guamá, in Belém, producing solutions which are similar to the ones produced by the nonlinear method but required a smaller computer time.Item Acesso aberto (Open Access) Uma nova abordagem na interpretação de anomalias gravimétricas em bacias sedimentares - exemplo da Bacia do Recôncavo, Bahia, Brasil(Universidade Federal do Pará, 1990-10-12) MENEZES, Paulo de Tarso Luiz; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491Item 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.