Deconvolução de Euler: passado, presente e futuro - um tutorial

Abstract

ABSTRACT. In this tutorial we present a historical overview of the evolution of Euler deconvolution method consisting of three sections. In the first section, we recall the Euler deconvolution 2D and 3D classic formulation as a method to automatically locate sources of potential fields anomalies and point out the difficulties of this formulation: the presence of an undesirable spray of solutions, the empiric criteria used to determine the structural index (a parameter related with the source nature), the feasibility of applying Euler deconvolution to small ground data survey, and the determination of the dip and susceptibility contrast of geological contact (or the product of the susceptibility contrast and the thickness when applied to thin dike). In the second section, we present recent improvements aiming at minimizing some of the difficulties presented in the first section. They include: i) selecting the solutions essentially associated with observations presenting the largest signal-to-noise ratios; ii) using the correlation between the estimated anomaly baselevel and the observed anomaly itself or combining Euler deconvolution with the analytic signal to determine the structural index; iii) combining the results from (i) and (ii) to allow estimating the structural index independently of the number of solutions so that a small number of observations (such as in a ground survey) may be used; and iv) introducing additional equations, which are independent from Euler's equation to estimate the dip and susceptibility of 2D sources. In the third section we provide a short-to medium-term outlook into future developments. The main prospects are: i) furthering the improvements on the problems singled out in the second section; ii) developing methods to take vertical and lateral interferences into accounts; and iii) incorporating Euler deconvolution to constrain the source location estimates and use them in inversion methods to obtain a source delineation in a user-friendly computer environment. Keywords:Euler Deconvolution, Automatic Potential Field Interpretations, Depth Estimation. RESUMO.Neste tutorial apresentamos uma revisão da deconvolução de Euler que consiste de três partes. Na primeira parte, recordamos o papel da clássica formulação da deconvolução de Euler 2D e 3D como um método para localizar automaticamente fontes de campos potenciais anômalas e apontamos as dificuldades desta formulação: a presença de uma indesejável nuvem de soluções, o critério empírico usado para determinar oíndice estrutural (um parâmetro relacionado com a natureza da fonte anômala), a exeqüibilidade da aplicação da deconvolução de Euler a levantamentos magnéticos terrestres, e a determinação do mergulho e do contraste de susceptibilidade magnética de contatos geológicos (ou o produto do contraste de susceptibilidade e a espessura quando aplicado a dique fino). Na segunda parte, apresentamos as recentes melhorias objetivando minimizar algumas dificuldades apresentadas na primeira parte deste tutorial. Entre estas melhorias incluem...

Structural framework of the Jaibaras Rift, Brazil, based on geophysical data

“…The structural index indicates source geometry. It is an exponential factor expressing the fall-off of the field strength versus distance from source ( Barbosa and Silva, 2005). The complexity degree or geometry of the magnetic source index varies from 0 to 3; the higher the value, the higher the tri-dimensionality of the sources (Reid et al, 1990).…”

Estudo comparativo entre duas anomalias magnéticas de corpos alcalinos no alto de cabo frio e em áreas proximais da bacia de santos apoiado por deconvolução de euler

“…A maior diferença encontrada (0,6) entre osíndices estruturais avaliados pelos dois primeiros critérios se verifica no perfil AB da Ilha de Cabo Frio, no qual os clusters azul e vermelho de soluções tendem a se separar. Em tese, a estimativa doíndice estrutural em ambientes geológicos complexos com múltiplas fontes interferentes permanece um problema sem solução para o método tradicional da deconvolução de Euler (Barbosa & Silva, 2005).É possível que a discordância entre as estimativas dosíndices estruturais pelos dois distintos critérios indique a presença de fontes interferentes próximas ou intenso ruído geológico.…”

Magnetometric Characterization of the Rio do Peixe Basin, Brazil

“…The method can be used to estimate the location of a wide variety of geological structures such as faults, magnetic contacts, dikes, and sills. These structures are classified by a parameter denominated as a structural index, which is related to the nature of the anomaly and is, according to Barbosa and Silva [16], the measurement of the magnetic anomaly decay rate with the distance between the source and measurement point. Table 2 compares geological models with the structural index for magnetic data.…”