HR: 16:30h
AN: U54A-03    [Abstracts]
TI: Post-Earthquake Multibeam Bathymetry and Backscatter Survey of 6400 sq. km. of the Accretionary Complex / Forearc in the Area of the Main 12 Sept. 07 Earthquake Rupture Zone
AU: * Orange, D L
EM: DOrange@BlackGoldEnergy.com
AF: Black Gold Energy LLC, Plaza City View 5th Floor Jl. Kemang Timur No. 22, Jakarta, 12510, Indonesia
AU: Teas, P A
EM: PTeas@BlackGoldEnergy.com
AF: Black Gold Energy LLC, Plaza City View 5th Floor Jl. Kemang Timur No. 22, Jakarta, 12510, Indonesia
AU: Decker, J
EM: JDecker@BlackGoldEnergy.com
AF: Black Gold Energy LLC, Plaza City View 5th Floor Jl. Kemang Timur No. 22, Jakarta, 12510, Indonesia
AU: Baillie, P
EM: peterb@tgsnopec.com.au
AF: TGS-Nopec, Level 5, 1100 Hay Street, West Perth, WA 6005, Australia
AU: Djajadihardja, Y S
EM: iyung@ceo.bppt.go.id
AF: BPPT, BPPT Building II - 19th Floor Jl. M. H. Thamrin No. 8, Jakarta, 10340, Indonesia
AU: Danque, H
EM: hdanque@gmail.com
AF: AOA Geophysics Inc., 7532 Sandholdt Rd., Suite 6, Moss Landing, CA 95039, United States
AU: Digby, A
EM: adrian_digby@aoageophysics.com
AF: AOA Geophysics Inc., 7532 Sandholdt Rd., Suite 6, Moss Landing, CA 95039, United States
AU: Rathore, S
AF: AOA Geophysics Inc., 7532 Sandholdt Rd., Suite 6, Moss Landing, CA 95039, United States
AU: Patton, J
EM: jpatton@coas.oregonstate.edu
AF: Oregon State University - College of Oceanic and Atmospheric Sciences, 104 COAS Admin. Building, Corvallis, OR 97331, United States
AB: When the 12 September M8.4 Southern Sumatra Earthquake hit, TGS-Nopec was carrying out a multibeam survey in the Sunda Straits, between Java and Sumatra. Working in collaboration with UTIG, OSU, BGR, and BPPT, we designed a 48 hour target-of-opportunity survey in the forearc region of the earthquake in an area where two trench perpendicular multibeam and seismic lines had previously been acquired by BGR. The objectives of the survey were to fill in an area of previously unsurveyed seafloor, and to acquire a data set for before and after comparison with the BGR data. Approx. 1100 line km of multibeam data were acquired between 17 and 20 September on a series of trench-perpendicular lines spaced 8km apart (weather limitations constrained the line orientation). Steep slopes and high backscatter seafloor result in some areas of data dropout. Using a fixed swath width and equi-distant beam spacing, bathymetric grids have been created at a range of scales that provide detailed imagery of the seafloor. The toe of slope is at ~6000m, with several normal faults cutting the seafloor on the incoming plate. The toe region of the accretionary complex shows individual folds 10-40km long, with both seaward and landward vergence. Fold wavelength is ~4km, with fold axes showing a trend slightly oblique to structures higher up on the accretionary complex. The folds in the toe region are cut by ENE trending high angle faults. 20km landward of the toe, in water depths of 5000-3000m, there is a 10km wide region of complex geomorphology and steeper slopes (locally 20 degrees and higher) showing a more degraded character with numerous slump headscarps and linear canyons 5-10km long. Although the slope is dissected by numerous slumps we observe no evidence for recent slope failure in the adjacent forearc basins. We interpret this region to be the seafloor projection of a significant thrust ramp in the accretionary complex. Landward of this area we identify 2 continuous ridges over 80km long, but that in detail show an irregular seafloor morphology. At 2500m water depth, 65km from the toe of slope, a significant geomorphic break with 10-20 degree slopes extends the length of the survey area, with water depths shoaling to 800m. We interpret this to be the surface projection of an out-of-sequence thrust. Although we identify some large debris blocks (>1km in length) in the adjacent forearc basin, the blocks appear rounded, with no obvious source or associated smaller scale debris that would suggest relatively recent emplacement. We find no clear evidence for any large recent slope failures associated with the M8.4 Earthquake or its aftershocks.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 3070 Submarine landslides
SC: Union [U]
MN: 2007 Fall Meeting