HR: 0800h
AN: T41C-0705    [Abstracts]
TI: Investigation on subduction erosion of the Central Costa Rica margin with seismic wide- angle data
AU: * Zhu, J
EM: jzhu@ifm-geomar.de
AF: IFM-GEOMAR,SFB574, Wischhof strasse 1-3, Kiel, 24148, Germany
AU: Flueh, E R
EM: eflueh@ifm-geomar.de
AF: IFM-GEOMAR,SFB574, Wischhof strasse 1-3, Kiel, 24148, Germany
AU: Kopp, H
EM: hkopp@ifm-geomar.de
AF: IFM-GEOMAR,SFB574, Wischhof strasse 1-3, Kiel, 24148, Germany
AU: Klaeschen, D
EM: dKlaeschen@ifm-geomar.de
AF: IFM-GEOMAR,SFB574, Wischhof strasse 1-3, Kiel, 24148, Germany
AB: Seismic wide-angle investigations along the Pacific margin off Central Costa Rica were carried out using closely spaced ocean bottom hydrophones and seismometers along two parallel strike and two parallel dip lines, intersecting at the mid slope. The structure and the P-wave velocities of the subducted oceanic Cocos Plate and overriding Carribean Plate were determined by modeling the wide-angle seismic data combined with the analysis of coincident reflection seismic data and the use of synthetic seismograms. Detailed velocity-depth distributions of two dip-lines and two strike-lines on the continental slope will be presented. Below the slope sediment, a wedge-shaped body, the margin wedge is defined by high velocities (4.3-6.1 km/s). This wedge shows a high velocity gradient zone in the uppermost one to two km, underlain by a low velocity gradient to the plate boundary. Between the subducted plate and overriding plate the low velocity zone including a lense-type structure is seen. This Megalens (4.0-4.3 km/s) and the subducted sediment comprise a low velocity zone (LVZ) all along the plate boundary. This LVZ is constrained by joint analysis of reflection seismic data and wide-angle data. The thickness of the wedge varies along the strike, this is associated with the subduction of the extension of Quepos Plateau, which also resulted in uplift of the margin. The extensional forearc environment is manifested by the normal faults indicated on the the multi-channel seismic (MCS) data. The Megalens is most probably comprised of material transferred from upper margin wedge at the tip of the wedge. The velocity structure within the Megalense resembles the velocities at the tip of the wedge, and is clearly lower than the oceanic crust, but higher thn subducted sediment. If this interpretation is valid, this material has been transported 16 km landward, which implies it was detached from the upper plate 0.2 Ma ago.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935, 7294)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting