HR: 1340h
AN: T53B-1418    [Abstracts]
TI: Small scale seismic velocities and change in fluid pressure along the decollement by 2D quantitative imaging
AU: Agudelo, W
EM: agudelo@geoazur.obs-vlfr.fr
AF: GEOSCIENCES AZUR-UMR 6526 IRD - Institut de Recherche pour le Developpement Observatoire Océanologique de Villefranche sur Mer, B.P. 48 Quai de la Darse, Villefranche-sur-mer, EU 06230 France
AU: * Ribodetti, A
EM: ribodeti@geoazur.obs-vlfr.fr
AF: GEOSCIENCES AZUR-UMR 6526 IRD - Institut de Recherche pour le Developpement Observatoire Océanologique de Villefranche sur Mer, B.P. 48 Quai de la Darse, Villefranche-sur-mer, EU 06230 France
AU: Collot, J
EM: collot@geoazur.obs-vlfr.fr
AF: GEOSCIENCES AZUR-UMR 6526 IRD - Institut de Recherche pour le Developpement Observatoire Océanologique de Villefranche sur Mer, B.P. 48 Quai de la Darse, Villefranche-sur-mer, EU 06230 France
AU: Operto, S
T53B-1418 AF: GEOSCIENCES AZUR-UMR 6526 IRD - Institut de Recherche pour le Developpement Observatoire Océanologique de Villefranche sur Mer, B.P. 48 Quai de la Darse, Villefranche-sur-mer, EU 06230 France
AU: Delouis, B
EM: delouis@geoazur.unice.fr
AF: GEOSCIENCES AZUR-UMR 6526 IRD - Institut de Recherche pour le Developpement Observatoire Océanologique de Villefranche sur Mer, B.P. 48 Quai de la Darse, Villefranche-sur-mer, EU 06230 France
AB: Numerous studies involving forward modeling and inversion of multichannel seismic reflection data have been carried out to constrain seismic velocity enhancement due to fluids inside and below the decollement and the presence of a low velocity zone associated with fluids in the sediment beneath it. However, the small scale velocities inside and below the decollement are still poorly known. We develop a technique based on conventional preserved amplitude prestack depth migration/inversion (PSDM) coupled with a specific post-processing of the tomographic model to analyse the physical properties along the decollement. The specific post-processing sequence allows us to: (1) mitigate effects of limited source bandwith and source-receiver aperture range from the tomographic images; (2) obtain the absolute values of the seismic velocities; (3) obtain the correct geometry of seismic reflectors reaching the theoretical seismic resolution of the source wavelet. During the post-processing sequence the model space exploration is made automatically via a random search, and optimal models are determined using the very fast simulated annealing algorithm. We present an application to multichannel seismic reflection data to obtain 2-dimensional quantitative imaging of the decollement on a profile located on the Ecuadorian margin. Preliminary results suggest that the decollement is a 50 to 70-m-thick layer with a generally negative velocity perturbation around -50 m/s that can reach locally values down to -150m/s. This relative velocity decrease is interpreted as changes in pore fluid pressure.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: Fall Meeting 2005