Margin structure and destabilisation processes on the Ecuador margin by 2D quantitative seismic imaging

HR: 1340h
AN: T33C-0571 [Abstracts]
TI: Margin structure and destabilisation processes on the Ecuador margin by 2D quantitative seismic imaging
AU: D'Acremont, E
EM: elia.dacremont@lgs.jussieu.fr
AF: UPMC Laboratoire de Tectonique, Case 129, T46-0, E2 4 Place Jussieu, PARIS, 75252 France
AU: D'Acremont, E
EM: elia.dacremont@lgs.jussieu.fr
AF: UMR GＰsciences Azur 6526 IRD-CNRS-UNSA, BP 48, Villefranche-sur-mer, 06235 France
AU: Ribodetti, A
EM: alessandra.ribodetti@geoazur.obs-vlfr.fr
AF: UMR GＰsciences Azur 6526 IRD-CNRS-UNSA, BP 48, Villefranche-sur-mer, 06235 France
AU: * Collot, J
EM: collot@obs-vlfr.fr
AF: UMR GＰsciences Azur 6526 IRD-CNRS-UNSA, BP 48, Villefranche-sur-mer, 06235 France
AU: Sage, F
EM: sage@obs-vlfr.fr
AF: UMR GＰsciences Azur 6526 IRD-CNRS-UNSA, BP 48, Villefranche-sur-mer, 06235 France
AB: We analyse multichannel seismic reflection (MCS) data collected during the SISTEUR cruise (2000) on the Nazca-north Andean convergent plate boundary in order to investigate the tectonic impact of gas hydrates and underthrusted asperities on the slope destabilization and the crustal thinning processes. We use preserved amplitude prestack depth migration method (PSDM) by considering four MCS lines, three perpendicular and one parallel to the margin. In order to get in depth, 2D quantitative image of seismic reflectors, the accuracy of the tomographic model is gradually improved by iterative corrections of the background velocity model. Close to the Carnegie ridge, the 9 km-thick oceanic crust has strong internal reflectors caused by the Galapagos hot spot activity. Through the margin, a seismic sequence composed of three acoustically strong reflectors images the top of the subducted oceanic crust, the inter-plate dＤollement, and the top of the upper margin. Common Image Gathers (CIG) panels are quite flat and semblance panels are around 1 on these layers. The plate interface is imaged acoustically strong, with discontinuous reflectors dipping landward from the trench, down to a maximum depth of 9-10 km below seafloor. The margin basement has been thinned seaward (less than 2km thick), broken up and uplifted. Seamounts of the Nazca oceanic crust are potential agents for basal erosion and deformation of the upper margin. On two crosscut profiles, the dＤollement dips seaward and strong deep reflectors beneath the upper margin indicate that a large seamount is in the process of being subducted. Shallower, the gas hydrate stability field, illustrated by bottom simulating reflectors (BSR) on seismic profiles, corresponds to a weakness zone. The triggering mechanisms of the slope failure depend on a combination of several parameters. The main one is probably an increase of the slope angle linked to the subduction of asperities like seamounts. A layer of decreased shear strength at the base of the gas hydrate stability field related to pressure or temperature change is another factor. In our study these two factors are joined.
DE: 3002 Continental shelf and slope processes (4219)
DE: 3004 Gas and hydrate systems
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005