HR: 0830h
AN: S11E-0339    [PDF]
TI: Empirical Synthesis of Green functions from the correlation of diffuse waves
AU: * Campillo, M
EM: Michel.Campillo@ujf-grenoble.fr
AF: LGIT Universite Joseph Fourier and CNRS, BP 53 X, Grenoble, 38042 France
AU: Larose, E
EM: Eric.Larose@ujf-grenoble.fr
AF: LGIT Universite Joseph Fourier and CNRS, BP 53 X, Grenoble, 38042 France
AU: Margerin, L
EM: Ludovic.Margerin@ujf-grenoble.fr
AF: LGIT Universite Joseph Fourier and CNRS, BP 53 X, Grenoble, 38042 France
AU: Paul, A
EM: Anne.Paul@ujf-grenoble.fr
AF: LGIT Universite Joseph Fourier and CNRS, BP 53 X, Grenoble, 38042 France
AU: van Tiggelen, B
EM: Bart.Van-Tiggelen@grenoble.cnrs.fr
AF: LPMMC Universite Joseph Fourier and CNRS, BP 166X, Grenoble, 38042 France
AU: Derode, A
EM: arnaud.derode@espci.fr
AF: LOA ESPCI and CNRS, 10 rue Vauquelin, Paris, 75005 France
AU: Abers, G
EM: abers@bu.edu
AF: Department of Earth Sciences, Boston University, 685 Commonwealth Ave, Boston, MA 02215 United States
AB: We show the existence of long range field correlations in the seismic coda of regional records in both Mexico and Alaska. The cross-correlation tensor between the coda records at two points is measured for a set of distant earthquakes. Remarkably, while individual correlations have a random character, the source- averaged correlations exhibit deterministic arrivals that obey the same symmetry rules as the Green tensor between the two points. In addition, the arrival times of these waves coincide with propagating surface waves between the two stations. Thus, we propose to identify the averaged correlation signals with the surface wave part of the Green tensor. However, while time reversal symmetry theoretically imposes that the Green function appears at both negative and positive times, we find experimentally this symmetry to be broken when the distribution of earthquakes is not isotropic around the stations. We explain this observation by the long lasting anisotropy of the diffuse field. This point is further discussed in a companion paper where we prove both experimentally and theoretically that a dominant flux of energy coming from the source can persist in the late coda. Finally, we show that averaged cross-correlations of ambient noise enable the reconstruction of some coherent arrivals. These examples illustrate a novel empirical method that provides synthetic seismograms between two stations, without the knowledge of the precise location and origin times of the sources.
DE: 0935 Seismic methods (3025)
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting