Estimating quality factor from surface seismic data: A comparison of current approaches |
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| Authors: | Bonnie Ives de Castro Nunes Walter Eugênio de Medeiros Aderson Farias do Nascimento José Antonio de Morais Moreira |
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| Institution: | aPrograma de Pós-graduação em Geodinâmica e Geofísica, Brazil;bDepartamento de Geofísica, Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte — UFRN, 59.072-970, NATAL, RN, Brazil;cINCT–GP. Instituto Nacional em Ciência e Tecnologia em Geofísica do Petróleo (CNPq), Brazil |
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| Abstract: | The performances of the spectral ratio (SR), frequency centroid shift (FCS), and frequency peak shift (FPS) methods to estimate the effective quality factor Q are compared. These methods do not demand true amplitude data and their implementations were done following an “as simple as possible” approach to highlight their intrinsic potentials and limitations. We use synthetic zero-offset seismic data generated with a simple layer-cake isotropic model. The methods can be ranked from simple to complex in terms of automation as: FPS, FCS and SR. This is a consequence of: (i) peak identification consists basically of a sorting procedure, (ii) centroid estimation involves basically the evaluation of two well-behaved integrals, and (iii) implementation of the SR method involves at least choosing a usable frequency bandwidth and fitting a gradient. The methods can be ranked from robust to sensitive in the presence of noise content in the sequence SR, FCS, and FPS. This is consequence of: (i) the gradient estimate associated to the SR method averages out the noise content in the entire usable frequency bandwidth, (ii) in the presence of moderate-to-high noise level, the centroid estimation is biassed towards overestimating Q due to noise contribution in the tail of the amplitude spectrum, and (iii) peak identification is unstable due to local noise fluctuation in the amplitude spectrum around the peak frequency. Regarding the stability of the estimates relative to the attenuation amount, SR and FCS methods show similar behaviours, whereas FPS method presents an inferior performance. This fact is an indirect consequence of the sensitivity of FPS method to the noise content because the higher is the attenuation the lower is the signal-to-noise ratio. Finally, regarding the robustness of the methods to the presence of dipping layers, only SR and FCS methods provide good estimates, at least to typical dips in non-faulted sedimentary layers, with the estimates obtained with SR method being more accurate that those obtained with FCS method. Except in relation to the automation complexity, which is less important than the performances of the methods, SR method was superior or showed similar performance to FCS method in all scenarios we tried. |
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| Keywords: | Attenuation Quality factor Comparison of Q estimates Spectral ratio Frequency centroid shift Frequency peak shift |
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