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Abstract:
Seismic interferometry is a methodology to recover the signals of waves propagating between seismic stations from records of
random wavefields such as the ambient seismic noise or the coda of an earthquake. Teleseismic body waves excited by a very
deep earthquake close to Kamchatka are investigated to unveil the composition of the teleseismic wavefield at long propagation
times which is key to understand how teleseismic waves can be reconstructed by seismic interferometry. Waves at high frequencies
around 1s period are shown to be scattered strongly in the Earth crust where they are quickly attenuated. At low periods,
seismic waves circle the Earth for many hours as surface waves with clear arrivals of the different orders. At intermediate periods
around 40s waves still propagate for several hours but individual arrivals cannot be identified in the data any more – indicating
a randomization process. It is shown here that to a large extent this randomization is due to the interaction with the Earth’s 1D
structure that does not alter the azimuthal distribution of the wavefield. Even after 8 h the seismic energy propagates dominantly
along the great circle and the mean free time of the azimuthal randomization is estimated to 10 h. This means that the recovery of
the teleseismic wavefield by seismic interferometry is strongly dependent on the distribution of ambient sources. For a successful
application of seismic interferometry sources need to be present at suitable distances on the great circle connecting the stations.
