Core Phases Retrieval from Cross-Correlations of Synthetic Seismic Coda

Traditional seismological observation detects the propagation of elastic waves through the Earth's interior using the energy from earthquakes, which is limited by the earthquake sources spatially and temporally. As a supplement, seismic interferometry constructs the Green's function between two receiver locations by cross-correlating the low-amplitude seismic noise waves recorded at these receivers, which avoid the limitation of geographical distribution of the natural earthquakes. However, the sources generating the body waves are uncertain. It has been suggested to come from the coda of large earthquakes (Lin et al., 2013) or from the ambient noise (Boue et al., 2014; Noshida 2013), which could be frequency-dependent (Boue et al. 2014). Due to the heterogeneities in the earth, coda waves travels through the interior of Earth with multiple reverberating and scattering, which tends to make the wavefield isotropic enough to follow the equipartition condition that required by seismic interferometry. We successfully retrieved body-wave core phases from synthetic coda waves with seismic interferometry. Our results show that reverberation is an important contribution to the source of the core phases signal at the long periods passband.