HR: 12:00h
AN: S52A-06    [Abstracts]
TI: Coherency of seismic noise, Green functions and site effects
AU: * Prieto, G A
EM: gprieto@stanford.edu
AF: Stanford University, 397 Panama Mall Mitchell Bldg Room 453B , Stanford, CA 94305, United States
AU: Beroza, G C
EM: beroza@pangea.stanford.edu
AF: Stanford University, 397 Panama Mall Mitchell Bldg Room 453B , Stanford, CA 94305, United States
AB: The newly rediscovered methodology of cross correlating seismic noise (or seismic coda) to retrieve the Green function takes advantage of the coherency of the signals across a set of stations. Only coherent signals are expected to emerge after stacking over a long enough time. Cross-correlation has a significant disadvantage for this purpose, in that the Green function recovered is convolved with the source-time function of the noise source. For seismic waves, this can mean that the microseism peak dominates the signal. We show how the use of the transfer function between sensors provides a better resolved Green function (after inverse Fourier transform), because the deconvolution process removes the effect of the noise source-time function. In addition, we compute the coherence of the seismic noise as a function of frequency and distance, providing information about the effective frequency band over which Green function retrieval is possible. The coherence may also be used in resolution analysis for time reversal as a constraint on the de-coherence length (the distance between sensors over which the signals become uncorrelated). We use the information from the transfer function and the coherence to examine wave propagation effects (attenuation and site effects) for closely spaced stations compared to a reference station.
DE: 0520 Data analysis: algorithms and implementation
DE: 3205 Fourier analysis (3255)
DE: 3270 Time series analysis (1872, 4277, 4475)
DE: 3285 Wave propagation (0689, 2487, 4275, 4455, 6934)
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: 2007 Fall Meeting