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AuthorsDe Lorenzo, S.* 
Del Pezzo, E.* 
Bianco, F.* 
TitleFrequency dependent Qα and Qβ in the Umbria-Marche (Italy) region using a quadratic approximation of the coda-normalization method
Issue Date2013
Series/Report no.3/193 (2013)
KeywordsSeismic attenuation
coda normalization method
Subject Classification04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis 
AbstractThe coda normalization method is one of the most used methods in the inference of attenuation parameters Qα and Qβ . Since, in this method, the geometrical spreading exponent γ is an unknown model parameter, the most part of studies assumes a fixed γ , generally equal to 1. However γ and Q could be also jointly inferred from the non-linear inversion of codanormalized logarithms of amplitudes, but the trade-off between γ and Q could give rise to unreasonable values of these parameters. To minimize the trade-off between γ and Q, an inversion method based on a parabolic expression of the coda-normalization equation has been developed. The method has been applied to the waveforms recorded during the 1997 Umbria-Marche seismic crisis. The Akaike criterion has been used to compare results of the parabolic model with those of the linear model, corresponding to γ = 1. A small deviation from the spherical geometrical spreading has been inferred, but this is accompanied by a significant variation of Qα and Qβ values. For almost all the considered stations, Qα smaller than Qβ has been inferred, confirming that seismic attenuation, in the Umbria-Marche region, is controlled by crustal pore fluids.
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