从漫射场的方位平均相干性反演衰减
On the retrieval of attenuation from the azimuthally averaged coherency of a diffuse field
摘要：
有人建议，地震衰减α可以从经验相干性（预白化的环境地震噪声记录的互谱）与衰减贝塞尔函数Jo（ωr/c）exp（-αr）的比较中推断出来。然而，分析表明，相干性强烈地依赖于环境噪声强度的方向性。即使相干性是方位平均的，建议的衰减相关性exp（-αr）也不适用。实际上，在高度定向的噪声场中，相干性与衰减无关。还认为相干性的空间和方位角平均值可能导致与可能模拟exp（-αr）等因素的波速变化相关的相位抵消。从经验相干性与Jo（ωr/c）exp（-αr）的比较中推断衰减是有问题的。
英文摘要：
It has been suggested that seismic attenuation αcan be inferred from comparisons of empirical coherencies (the cross spectra of pre-whitened ambient seismic noise records) with attenuated Bessel functions Jo(ωr/c) exp(-αr). Analysis shows here, however, that coherency depends strongly on the directionality of ambient noise intensity. Even if coherency is azimuthally averaged, the suggested attenuation dependence exp(-αr) does not apply. Indeed in highly directional noise fields, coherency is independent of attenuation. It is also argued that spatial and azimuthal averages of coherency can incur phase cancellations related to variations in wavespeed that may mimic factors like exp(-αr). Inference of attenuation from comparison of empirical coherencies to Jo(ωr/c) exp(-αr) is problematic.
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