Faculdade de Geofísica - FAGEOF/IG
URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2544
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Navegando Faculdade de Geofísica - FAGEOF/IG por Autor "COSTA, Jessé Carvalho"
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Item Acesso aberto (Open Access) 3D raytracing through homogeneous anisotropic media with smooth interfaces(2002-12) COSTA, Jessé Carvalho; SCHOENBERG, Michael; URBAN, Jaime AntonioTwo-point raytracing problem is solved for events in a piecewise homogeneous and laterally varying 3D anisotropic media by continuation techniques. In conjunction with the shooting method the algorithm can be used for computation of qP, qS1, and qS2 events. The algorithm has the same performance and robustness as previous implementations of the continuation method for tracing rays in isotropic models. Routines based on our algorithm have several useful applications. First, an efficient forward problem solver for traveltime inversion of elastic parameters in the presence of anisotropy. Second, Newton-Raphson iterations during two-point raytracing produce wavefront attributes, slowness and wavefront curvature. These attributes allows the computation of geometrical spreading and second order approximations for traveltimes. Therefore it can be used to investigate the effects of anisotropy on CRS, in simple velocity models.Item Acesso aberto (Open Access) Linearização dos coeficientes de reflexão de ondas qP em meios anisotrópicos(2001-04) GOMES, Ellen de Nazaré Souza; PROTÁZIO, João dos Santos; COSTA, Jessé Carvalho; SIMOES FILHO, Ivan A.The reflection coefficients at a planar interface separating two anisotropic media have a nonlinear dependence on the elastic parameters and densities of both media. Linear approximations on the elastic parameters for the qP wave reflectivity are more convenient for AVO/AVD analysis. We present the solution of the Zoeppritz equations in terms of impedance and polarization matrices. Using this approach and assuming weak impedance contrast and weak anisotropy, a simple derivation of linearized approximations for qP the reflectivity is presented for general anisotropy. The linear approximations of reflection coefficients, qP and converted waves, for qP incidence are very close to the exact results for incidence angles up to 30 degrees considering moderate impedance contrast and anisotropy.Item Acesso aberto (Open Access) Wave equation depth migration using complex Padé approximation(2009-03) PESTANA, Reynam da Cruz; LUCAS, Jacira Cristina de Freitas; COSTA, Jessé CarvalhoWe propose a new method of depth migration based on a constant density variable velocity wave equation in the space-frequency domain. A complex Padé approximation of the wave equation evolution operator is used for wavefield extrapolation. This method mitigates the inaccuracies and instabilities due to evanescent waves and produces images with fewer numerical artifacts than those obtained with a real Padé approximation of the exponential operator, mainly in media with strong velocity variations. Tests on zero-offset data from the SEG/EAGE salt model and the 2D Marmousi prestack dataset show that the proposed migration method can handle strong lateral variations and also has a good steep dip response. We compare the results of the proposed method with those obtained using split-step Fourier (SSF), phase shift plus interpolation (PSPI) and Fourier finite-difference (FFD) methods.