HR: 16:30h
AN: U14A-02    [Abstracts]
TI: Evidence for Seafloor Deformation During Great Subduction Zone Earthquakes of the Sumatran Subduction zone: Results From the First Seafloor Survey Onboard the HMS Scott, 2005
AU: * McNeill, L
EM: lcmn@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, Southampton, UK SO14 3ZH United Kingdom
AU: Henstock, T
EM: then@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, Southampton, UK SO14 3ZH United Kingdom
AU: Tappin, D
EM: drta@bgs.ac.uk
AF: British Geological Survey, Keyworth, Nottingham, UK NG12 5GG United Kingdom
AB: The 26 December 2004 Mw 9.3 Sumatra-Andaman Islands subduction zone earthquake was the second largest earthquake recorded with fault slip up to 10-25 m and provided the first opportunity to investigate evidence of seafloor deformation immediately after an event of this size. The Royal Navy's HMS Scott conducted a bathymetric survey over the rupture zone during Jan-Feb, 2005. The data reveal the geomorphology of the deformation front, accretionary wedge, outer-arc high fault system and forearc basin of the southern 2004 rupture zone. Primary surface rupture during large thrust/reverse fault earthquakes is rare and complex and the nature of shallow slip during submarine subduction zone events is particularly poorly known. Data from the southern part of the 26/12/04 rupture zone reveal numerous small neotectonic features at the toe of the accretionary prism. These take the form of scarps, folds and depressions 5-100 m in height on the seaward limb of the frontal thrust ridges. If these features are formed during coseismic slip and slip is focused on a few faults, they may represent slip during a few or possibly a single great earthquake. The morphology of the frontal thrusts strongly suggests landward-vergent (seaward-dipping) faulting. A model of backthrust fault slip or bending moment folding during coseismic plate boundary slip can explain the position of these features on the seaward fold limb of the frontal thrust. We suggest that rupture may propagate to the seafloor close to the deformation front in major plate boundary earthquakes.
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8004 Dynamics and mechanics of faulting (8118)
SC: Union [U]
MN: Fall Meeting 2005