Navegando por Assunto "Steptoe Valley - NV"

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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/1870725463184491
We 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.
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/1870725463184491
We 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.
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/5813659873067927
We 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.