Reverberations, coda waves and ambient noise: Correlations at the global scale and retrieval of the deep phases

- Body-waves retrieval from cross-correlation of continuous records.
- Global scale interferometry in the 5 s to 100 s period band.
- Impact of reverberated waves from large earthquakes.

Cross-correlation of continuous broadband records allows the retrieval of body waves at teleseismic distances. These continuous records mainly contain low-amplitude background noise that comes from ocean-crust interactions, although there are also many transient events of different magnitudes and their coda associated with reverberation and/or scattering. We present an analysis at the global scale of these different contributions in the context of body-wave retrieval using the cross-correlation technique. Specifically, we compare the correlation of long codas after strong earthquakes with those of the quietest days. In the long period range (25-100 s), several phases that propagate in the deep Earth are observed in the correlations of the signals recorded after earthquakes, with some of these phases showing non-physical polarization. At the same time, the global section of correlations shows a series of spurious branches. These features are reproduced with synthetic correlations. A stack of the quietest days of the year shows that body waves are still present, with relative amplitudes that are closer to those expected for the actual Earth response. When considering shorter periods (5-10 s), the reconstruction of the deep phases is not affected by the earthquake coda, due to the dominance of scattering over reverberation.