HR: 14:40h
AN: S23D-05 INVITED    [Abstracts]
TI: Results from SCS Profiling of the Sumatra accretionary prism: insights into tsnamigenesis
AU: * Fisher, D
EM: fisher@geosc.psu.edu
AF: Pennsylvania State University, Department of Geosciences, University Park, PA 16802,
AU: Mosher, D
EM: dmosher@nrcan.gc.ca
AF: Geological Survey of Canada-Atlantic, 1 Challenger Dr., Dartmouth, B2Y 4A2, Canada
AU: Austin, J
EM: jamie@utig.ig.utexas.edu
AF: University of Texas, Institute for Geophysics, Austin, TX 78759-8500, United States
AU: Gulick, S
EM: sean@utig.ig.utexas.edu
AF: University of Texas, Institute for Geophysics, Austin, TX 78759-8500, United States
AU: Moran, K
EM: kate.moran@uri.edu
AF: University of Rhode Island, Graduate School of Oceanography and Engineering, Naragansett, RI 02882, United States
AU: Masterlark, T
EM: masterlark@geo.ua.edu
AF: University of Alabama, Department of Geological Sciences, Tuscaloosa, AL 35487, United States
AB: The SEATOS high resolution single-channel seismic reflection survey of the Sumatran accretionary prism depicts a landward-vergent thrust front, with active folding characterizing part of the December 2004 Mw9.2 earthquake rupture zone. Structure and bathymetry co-vary at distinct wavelengths along a 220-km-long profile crossing the prism and the Aceh (forearc) Basin. At the largest wavelength (tens of kms), the prism surface is defined by a steep (8-12 degrees), 55-km-wide outer slope, a 110-km-wide upper slope forming a broad depression between two forearc highs, and a 25 km-wide, steep inner slope between the landward high and the forearc basin. Anticlinal ridges spaced ~13 km apart display landward- and seaward-vergent folds along the inner and outer slopes, respectively; symmetric folding occurs across the upper slope. We suggest that the long-wavelength variations are consistent with the existence of a strong inner wedge beneath the upper slope. The ~13 km anticline spacing implies deformation of a slope apron deforming independently of this stronger wedge interior. Seismic profiles crossing the toe of the prism image a series of landward vergent, fault-related folds, suggesting that the shallow fill of the Sunda Trench is delaminated from the predominantly seaward-vergent plate boundary system and is uptilted along a triangle zone. Profiles crossing the seaward flank of the Aceh Basin reveal a near- vertical, undulatory deformation front that appears to mark the location of the West Andaman-Mentawai right- lateral strike-slip fault zone. Our model for prism architecture based on these geophysical results involves advance of the strong inner wedge during great earthquakes like the 2004 event, which then peels up shallower and less competent trench fill, deforming the toe and the upper slope of the forearc, producing massive uplift that is likely tsunamigenic. Seismic rupture was limited to the megathrust westward of the West Andaman fault and ROV observations showed no evidence for surface rupture along the strike-slip fault system. These results suggest strong strain partitioning along this oblique margin and highlight the hazards represented by the West Andaman and Sumatran faults.
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: 8005 Folds and folding
DE: 8123 Dynamics: seismotectonics
SC: Seismology [S]
MN: 2007 Fall Meeting