HR: 11:05h
AN: S52A-03 INVITED    [Abstracts]
TI: Identifying Higher-Mode Surface Waves From Noise Cross-Correlations
AU: * Baig, A M
EM: Adam.Baig@obs.ujf-grenoble.fr
AF: LGIT Université Joseph Fourier, BP 53, Grenoble Cedex 9, 38041, France
AU: Campillo, M
EM: Michel.Campillo@obs.ujf-grenoble.fr
AF: LGIT Université Joseph Fourier, BP 53, Grenoble Cedex 9, 38041, France
AB: The cross-correlations of seismic noise over long distances offers a new type of data in geophysical studies. Recognizing that the cross-correlation between stations is proportional to the elastic Green's function, we can free ourselves of the resolution problems inherent in illuminating a study area from the uneven distribution of earthquakes: an even distribution of stations over the study area will allow for even resolution. However, because earthquakes occur at various depths, they can excite certain phases much more energetically than those observed in the cross-correlation data, which are dominated by the fundamental-mode surface wave. These higher-mode surface waves and body wave phases are sensitive to deeper structures within the Earth compared to the fundamental mode. Though these higher-mode surface waves and body waves are subdued, they are present in the noise cross-correlations. We use a time-frequency stacking algorithm, based on the S-transform, coupled with a filter designed from the multi-channel coherence across an array, to enhance these faster arrivals. We observe a coherent phase arriving well before the fundamental-mode surface waves that we interpret to be a higher-mode surface wave. Observations like these will be necessary to take advantage of the increased resolution offered by noise cross-correlations input into tomographic inversions while simultaneously placing constraints on upper mantle structure.
DE: 3255 Spectral analysis (3205, 3280)
DE: 7200 SEISMOLOGY
DE: 7255 Surface waves and free oscillations
SC: Seismology [S]
MN: 2007 Fall Meeting