Frequency dependent Qα and Qβ in the Umbria-Marche (Italy) region using a quadratic approximation of the coda-normalization method
Frequency dependent Qα and Qβ in the Umbria-Marche (Italy) region using a quadratic approximation of the coda-normalization method
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DOI：
10.1093/gji/ggt088
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发表时间：
2013-06
影响因子：
2.8
通讯作者：
S. Lorenzo;F. Bianco;E. Pezzo
中科院分区：
文献类型：
--
作者：
S. Lorenzo;F. Bianco;E. Pezzo
尾波归一化法是推断衰减参数Qα和Qβ最常用的方法之一。由于在这种方法中，几何扩展指数γ是一个未知的模型参数，因此大多数研究都假设γ是固定的，通常等于1。然而，γ和Q也可以从振幅的码归一化谱的非线性反演中联合推断，但是γ和Q之间的折衷可能导致这些参数的不合理值。为了最小化γ和Q之间的折衷，已经开发了基于尾波归一化方程的抛物线表达式的n反演方法。该方法已被应用于1997年翁布里亚-马尔凯地震危机期间记录的波形。Akaike准则已被用于比较抛物线模型与线性模型的结果，对应于γ = 1。已经推断出与球形几何扩展的微小偏差，但这伴随着Qα和Qβ值的显著变化。对于几乎所有考虑的台站，Qα都小于Qβ，证实翁布里亚-马尔凯地区的地震衰减受地壳孔隙流体控制。
SUMMARY 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 ,a n 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.