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TitleDeformation of the northern Sumatra accretionary prism from high-resolution seismic reflection profiles and ROV observations
AuthorMosher, D CORCID logo; Austin, J A, Jr; Fisher, D; Gulick, S P S
SourceMarine Geology vol. 252, issue 3-4, 2008 p. 89-99,
LinksSupplementary Data - Données supplémentaires
Alt SeriesEarth Sciences Sector, Contribution Series 20070360
Alt SeriesUniversity of Texas, Institute for Geophysics, Contribution 1983
PublisherElsevier BV
Mediapaper; on-line; digital
File formathtml; pdf (Adobe® Reader®)
AreaIndian Ocean; northern Sumatra; Sunda Trench; Aceh Basin; Indonesia
Lat/Long WENS 91.5000 95.2500 6.0000 3.0000
Subjectsgeophysics; tectonics; marine geology; structural geology; deformation; geophysical surveys; seismic reflection surveys; seismic profiles, marine; plate tectonics; plate margins; subduction zones; tectonic setting; tectonic elements; tectonic evolution; tectonic interpretations; displacement; accretion; bathymetry; structural analyses; structural features; faults; faults, normal; faults, strike-slip; folds; joints; fractures; basin evolution; subsidence; sedimentation; sedimentary structures; bedding planes; talus; marine sediments; mass wasting; earthquakes; seismicity; strain; tsunami; photogeology; photography; 2004 Great Sumatran-Andaman earthquake; West Andaman Fault zone; Indian-Australian Plate; Aceh Plate; Burma Plate; multibeam bathymetry; remotely operated vehicle (ROV) observations; videos; deformation zones; accretionary wedges; thrust folds; forearcs; basin fill; sediment samples; biological samples; plumose structures
Illustrationssketch maps; digital elevation models; seismic reflection profiles; photographs; block diagrams
ProgramGeoscience for Oceans Management, Geohazards and Constraints to Offshore Development
AbstractFollowing the 2004 Great Sumatran-Andaman Mw ~9.2 earthquake, high-resolution seismic reflection, multibeam bathymetric and remotely operated vehicle data were acquired to investigate the tectonic framework of the rupture zone and search for evidence of seafloor and near-surface displacement. Three distinct regions off northern Sumatra were investigated; 1) a portion of the Sunda Trench, 2) the adjacent
frontal deformation zone, and 3) the seaward flank of the Aceh (forearc) Basin. A thick (N1.5 km) sediment section within the Sunda Trench shows evidence of shallow normal faulting, possibly representing early stages of assimilation into the accretionary wedge. The frontal deformation zone consists of ridges of predominantly landward-verging thrust folds. Seaward-verging backthrust faults at or near the base of the steep slope commonly reach the seafloor. We do not observe a single, laterally extensive structural offset at the deformation front that might be interpreted as contributing to the 2004 tsunami. Rather, a series of small-offset (tens of metres) faults were noted across this broad zone of the frontal accretionary wedge. The western boundary of the Aceh (forearc) Basin is the West Andaman strike-slip fault, juxtaposing the accretionary complex's forearc high with basin fill sediments. Neither the seismic nor ROV data show evidence of recent seafloor displacement along the fault trace. Basin infill demonstrates consistent alongstrike patterns of tilting and seaward subsidence during sedimentation, while modern fill is flat-lying and coherent across the entire basin. Intercalated chaotic layers interpreted as mass transport deposits may record a history of seismicity, but recent examples of such deposits were not observed on the modern seafloor, either seaward of the deformation front or in the Aceh Basin. Lack of any evidence of faulting, offset or disruption of sediments within Aceh Basin suggests that there was little impact of the 2004 earthquake in this area. Distributed faults throughout the frontal deformation zone, combined with observations of landward-verging folds at the deformation front, folding within piggy-back basin sediments, and lack of
evidence of disruption along the West Andaman Fault zone and within the forearc basin all support strain partitioning across the margin. A proposed strong wedge interior may act as a backstop during major thrust events, constraining deformation to the frontal deformation zone and the slope apron. Tsunami generation in response to the 2004 event did not result from surficial displacements along a single fault or narrow fault zone at the toe of the deformation front, but was more likely a result of vertical displacement across the entire outer forearc.

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