HR: 15:10h
AN: S53D-06    [Abstracts]
TI: The 7-sec Microseism Origin Investigated From Amplitude Variations and Polarization of Noise.
AU: * Stutzmann, E
EM: stutz@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, 75005, France
AU: Schimmel, M
EM: schimmel@ija.csic.es
AF: Institute of Earth Sciences "Jaume Almera" - CSIC, Lluis Sole i Sabaris s/n, Barcelona, 08028, Spain
AU: Patau, G
EM: patau@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, 75005, France
AU: Weissenbach, D
EM: weissen@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussieu, Paris, 75005, France
AB: In the absence of earthquakes, broadband seismic signal is dominated by a peak of noise around 7 sec of period, called microseisms. Variations of this peak amplitude are investigated using the 30 stations of the GEOSCOPE global network. For each station, power spectrum estimates of the seismic noise are averaged over sequences of 24 hours. The noise level of 10 years of continuous data has been computed. Variations of the seismic noise amplitudes are similar every year. We observe seasonal variations of the 7-sec microseismic peak that are correlated with the station latitude. For stations close to the equator the peak has constant low amplitude over the year. The maximum amplitude of the 7-sec peak is observed for stations in the southern hemisphere between June and September that is during local winter. Similarly, high noise level is observed for stations in the Northern hemisphere between November and February but with smaller amplitude than in the Southern hemisphere. These noise level variations are well correlated with the location and intensity of storms in the oceans that are stronger and more frequent in winter. In order to locate the source of the microseisms, we systematically computed the degree of polarization of noise sequences and when the noise is polarized, the source back azimuth is estimated using the method of Schimmel and Gallart (2004). The computation is performed using EGEE computing grid. The variation of the microseim sources can then be followed over the year and compared to the storm locations.
DE: 7200 SEISMOLOGY
DE: 7255 Surface waves and free oscillations
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: 2007 Fall Meeting