HR: 16:15h
AN: S54B-02    [Abstracts]
TI: PP/PS Wavefield separation by independent component analysis
AU: * van der Baan, M
EM: earmarvb@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment: Earth Sciences, Leeds, LS2 9JT, United Kingdom
AB: In blind signal separation one seeks to retrieve the original source signals that are observed as a linear mixture on an array of sensors. No a priori information is available about waveforms or polarisations of the desired source signals -- hence the term blind. Blind signal separation can be achieved using independent component analysis (ICA) which is a rapidly emerging technology in the field of advanced signal processing. It separates a set of observed signals into the statistically most independent components by appealing to higher-order statistics. ICA retrieves the original source signals blindly if they are statistically independent without the need of further a priori information. There are many promising applications of ICA in geophysical signal analysis. ICA can be used to separate P- and S-waves in 3-component seismic reflection data without knowledge of P- and S-wave near-surface velocities or density. Multi-trace recordings are first transformed to the tau-p domain (i.e., intercept time versus horizontal slowness). It is next assumed that a thin laterally homogeneous layer exists at the surface such that all incoming P-waves with the same slowness have the same incidence angle. The same is then true for all incoming S-wave energy as well. Wavefield separation is then achieved by exploiting statistical differences between P- and S-waves only. An inverse tau-p transform yields finally the desired PP and PS wavefields in the time-offset domain. The usual problems of amplitude indeterminacy and signal identification that occur in ICA are overcome by examining the inner products of the independent comp onents with the original observations to ensure that the retrieved P- and S-waves have the appropriate signs and energies. Mode identification is realised by comparing current polarisations with forward predicted ones for each mode while maximising the coherence with previously determined modes. The ICA wavefield separation technique is exact in a laterally inhomogeneous an isotropic Earth with a homogeneous anisotropic near-surface layer if only upgoing waves are present.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
SC: Seismology [S]
MN: 2007 Fall Meeting