Inter-source body wave propagations derived from seismic interferometry

P>Seismic interferometry combined with source-receiver reciprocity has recently been employed to extract inter-source wave propagations. In this study, we applied the technique to seismograms of earthquakes that occurred at depths of 300-500 km beneath the Bonin Islands. The wavelets of direct P- and S-waves generated by the deep earthquakes were examined to compute cross-correlation functions (CCFs). We stacked the CCFs observed at receivers around the stationary point whose location could be estimated by the ray tracing technique, because the phases in such CCFs potentially emerge at similar lag times; that is the stationary phases. The results demonstrate the retrieval of direct P- and S-waves propagating between pairs of deep earthquakes; in particular, direct P waves are reconstructed for most event pairs. The following points should be considered to effectively retrieve the propagation of body waves: (1) it is important to design a geometry in which the stationary phase derived from two earthquakes can be observed at the employed stations, (2) the lag time difference of the stationary phases that emerge in the employed CCFs should be as small as possible and (3) the direct waves associated with deep earthquakes have a large amplitude at stations employed for cross-correlation, which is accomplished by both low noise level at the stations and the radiation pattern of the sources.