HR: 0800h
AN: S31A-0264    [Abstracts]
TI: Origin of the Seismic Noise Investigated From its Correlation Properties.
AU: * Stehly, L
EM: Laurent.Stehly@obs.ujf-grenoble.fr
AF: LGIT, Universite Joseph Fourier and CNRS, Maison des Geosciences, BP 53, Grenoble, 38041 France
AU: Campillo, M
EM: Michel.Campillo@ujf-grenoble.fr
AF: LGIT, Universite Joseph Fourier and CNRS, Maison des Geosciences, BP 53, Grenoble, 38041 France
AU: Shapiro, N M
EM: nshapiro@fignon.colorado.edu
AF: Laboratoire de Sismologie, 5 Place Jussieu, Paris, 75005 France
AB: We studied the apparent origin of the noise by cross-correlating the vertical component of one year of continuous records of seismic ambient noise at several networks located in North-America, Europe and Tanzania. We measured the amplitude ratio of the Rayleigh waves reconstructed from correlation (Shapiro and Campillo, GRL 2004) for all available station to station paths within the networks for positive and negative correlation times. We determined the seasonally averaged azimuthal distribution of energy flow through the network for 3 different bandwidths: 5-10s, 10-20s and 20-40s. Results for California show that for periods between 5 and 10s the noise is always coming from the coastline. The noise in the band 10-20s is season dependent and has the same apparent origin than for periods between 20 and 40s. This suggests that it is produced by the same mechanism while the noise between 20-40s is not likely produced by the direct action of the swell. Others mechanisms have to be invoked. This means that at periods as short as 15s, the noise could be related to the same source as for long period, namely infragravity waves in the deep ocean. By performing the same analysis with networks in Europe, Tanzania, Eastern US, we were able to identify the main source regions for the noise in the period band between 10 and 20s. They are mainly North Atlantic and north Pacific ocean during the winter and south Indian and pacific ocean during the summer. These distribution of sources share a great similarity with the map of average ocean wave height map obtained by TOPEX-POSEIDON. This suggests that the seismic noise for period larger than 10 s is clearly related to ocean wave activity in deep water.
DE: 4560 Surface waves and tides (1222)
DE: 7200 SEISMOLOGY
DE: 7255 Surface waves and free oscillations
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: Fall Meeting 2005