Can complete Green's function be retrieved from ambient seismic noise?

Theoretical studies on ambient seismic noise (ASN) predict that complete Green's function between seismic stations can be retrieved from cross correlation. However, to date only surface waves portion of the Green's function has been retrieved in most studies involving real data. Here using seismic arrays in the Kaapvaal craton (South Africa) and the Great Slave Lake region (northern Canada), we show that Moho-reflected body wave (SmS) and its multiples near their critical distances can be identified with ASN. This is expected because previous studies showed that SmS and its multiples have comparable amplitude to surface waves when the crustal structure is simple (Mori and Helmberger, 1996). By detailed array analysis of the cross correlation functions, we show that the precursors before surface waves are caused by an uneven distribution of noise sources, such as mining activity and wind-topography-interaction, can cause surface wave precursors. These precursors can mask weaker body wave phases. We specifically found that “voids” or “holes” in noise source distribution cause surface wave precursors as well. These results imply that to obtain the complete Green's function requires a better understanding of the noise sources.