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《Chinese Journal of Geophysics》 2016-09
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On the spatial correlation of seismic noise in an attenuating medium

WANG Kai-Ming;LU Lai-Yu;LIU Qing-Hua;Institute of Geophysics,China Earthquake Administration;  
Traditionally,the tomography based on the correlation of seismic noise primarily uses the phase information of ambient noise correlation function(NCF)to extract the seismic velocity and anisotropy of the Earth with travel time measurement by performing inversion.Researchers recently utilize the amplitude of NCF to extract the Earth′s attenuation.In theory,NCF is proportional to the first kind of zero-order Bessel function in a 2-D elastic case,which is directly extended to the dissipative media by introducing an exponential attenuation coefficient.The attenuation of the structure is then obtained by comparing the observed data from NCF to the Bessel function multiplied by a decaying exponential term.The NCF,however,is affected by azimuth averaging of ambient noise sources distributed in attenuated media.This empirical and simple extension cannot be used to extract a reliable decay coefficient.In this paper,we study the theoretical expressions of NCF in the frequency domain between two stations under different coordinate systems and accordingly different source distributions which are composed ofsuperposition of plane waves.We show that the coherency expressions in dissipative media vary with coordinate systems.The expressions are different for different normalized factors.The attenuation coefficient obtained by fitting the coherency J_0(k_0r)·e~(-α(ω)r) with the observed data is smaller than the real one.
【Fund】: 国家自然科学基金(41174041)资助
【CateGory Index】: P631.4
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