Empirical Green's function (EGF) retrieval and turning ambient noise into useful signal by crosscorrelation or seismic interferometry (Curtis et al., 2006) has been a popular topic in recent years in the seismological community. Many have discussed how the interstation distance or its equivalent affects the accuracy of the Green's function that can be retrieved by crosscorrelation of long-range noise between two stations (e.g., Snieder, 2004; Bensen et al., 2007; Halliday and Curtis, 2008; Tsai, 2009; Kimman and Trampert, 2010). It is generally accepted that the necessary or optimum interstation distance strongly depends on source distribution, length of records (and, hence, is naturally related to source distribution), and the duration of the Green's function to be retrieved. Noise generated by a surface source can be efficiently used to reconstruct the Green's function of surface waves if we focus on the accuracy of the phase, and not be too concerned with the amplitude accuracy of the retrieved Green's function (Halliday and Curtis, 2008; Kimman and Trampert, 2010).

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