Long-Range Correlations in the Diffuse Seismic Coda

TLDR

The late seismic coda may contain coherent information about the elastic response of Earth. We computed the correlations of the seismic codas of 101 distant earthquakes recorded at stations that were tens of kilometers apart. Stacking cross‑correlation functions of codas revealed a low‑frequency coherent component whose Rayleigh and Love wave pulses exhibit expected polarization and group velocities, the cross‑correlations possess the surface‑wave Green tensor symmetries, and the results demonstrate that diffuse waves from distant sources can recover direct waves between two points, suggesting broader applications.

Abstract

The late seismic coda may contain coherent information about the elastic response of Earth. We computed the correlations of the seismic codas of 101 distant earthquakes recorded at stations that were tens of kilometers apart. By stacking cross-correlation functions of codas, we found a low-frequency coherent part in the diffuse field. The extracted pulses have the polarization characteristics and group velocities expected for Rayleigh and Love waves. The set of cross-correlations has the symmetries of the surface-wave part of the Green tensor. This seismological example shows that diffuse waves produced by distant sources are sufficient to retrieve direct waves between two perfectly located points of observation. Because it relies on general properties of diffuse waves, this result has potential applications in other fields.