HR: 0800h
AN: U11A-0806    [Abstracts]
TI: Seafloor Morphology of the 26 December, 2004 Earthquake Rupture Zone: Results From the First Seafloor Survey Onboard the HMS Scott, 2005
AU: * Henstock, T
EM: then@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, Southampton, SO14 3ZH United Kingdom
AU: McNeill, L
EM: lcmn@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, Southampton, SO14 3ZH United Kingdom
AU: Tappin, D
EM: drta@bgs.ac.uk
AF: British Geological Survey, Keyworth, Nottingham, NG12 5GG United Kingdom
AB: The 26 December 2004 Sumatra to Andaman Islands subduction zone earthquake was the second largest earthquake recorded. The Royal Navy's HMS Scott conducted the first multibeam bathymetric survey over the rupture zone in early 2005. This is the first time a high resolution deep-water survey has been carried out so soon after an earthquake of this magnitude. Existing geophysical data in the earthquake rupture zone are rare and therefore the general subduction zone structure is poorly known. Data were collected in the southern and initial part of the rupture zone offshore Sumatra, including the plate boundary and lower accretionary prism, the southern termination of the earthquake rupture and probable segment boundary, and parts of the forearc basin and outer arc high system. The lower prism forms a steep slope (up to 15 percent) which then levels onto a broad plateau and extends landward to the outer-arc high and forearc basin. The prism is heavily eroded except for the youngest frontal thrusts, due to low terrestrial sediment input which ponds in the forearc basin. Segmentation of the frontal thrust ridges reflects the major segment boundary and change in trend of the deformation front at the southern termination of the 2004 rupture. The asymmetry of many of the youngest thrust ridges suggests they are underlain by seaward-dipping (landward-vergent) faults. Pull-apart basins and shear zones associated with NNW-trending dextral faulting are common along the outer-arc high structure (West Andaman fault) at the seaward edge of the forearc basin.
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