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http://hdl.handle.net/2122/8639
Authors: | De Lorenzo, S.* Del Pezzo, E.* Bianco, F.* |
Title: | Frequency dependent Qα and Qβ in the Umbria-Marche (Italy) region using a quadratic approximation of the coda-normalization method | Journal: | Geophysical Journal International | Series/Report no.: | 3/193 (2013) | Publisher: | Wiley-Blackwell | Issue Date: | 2013 | DOI: | 10.1093/gji/ggt088 | Keywords: | Seismic attenuation coda normalization method |
Subject Classification: | 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis | Abstract: | The 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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