HR: 16:45h
AN: U14A-03    [Abstracts]
TI: Landslides and mass wasting offshore Sumatra - results from the Sumatra Earthquake HMS Scott survey January-February 2005
AU: * Tappin, D R
EM: drta@bgs.ac.uk
AF: British Geological Survey, Kingsley Dunham Centre Nicker Hill, Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Henstock, T
EM: then@soc.soton.ac.uk
AF: National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH United Kingdom
AU: McNeill, L
EM: lcmn@noc.soton.ac.uk
AF: National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH United Kingdom
AU: Grilli, S
EM: grilli@oce.uri.edu
AF: University of Rhode Island, Department of Ocean Engineering, Narragansett, RI RI 02882 United States
AU: Biscontin, G
EM: gbiscontin@tamu.edu
AF: Texas A&M University, Department of Civil Engineering, College Station, Houston, TX TX 7843-31 United States
AU: Watts, P
EM: Philwatts@appliedfluids.com
AF: Applied Fluids Engineering, inc, Private Mail Box #237, 5710 E. 7th Street, Long Beach, CA 90803 United States
AB: Earthquakes are a commonly cited mechanism for triggering submarine landslides that have the potential to generate damaging tsunamis (e.g. Papua New Guinea 1998). Notwithstanding, the Indian Ocean earthquake of December 26th 2005 has been cited as the cause of both far field and local tsunami runups that have been measured at over 35 metres on the west coast of Sumatra. On the basis of present modelling this seems to be the case. However, if earthquakes are such a common trigger for landslides then the magnitude 9.3 earthquake of December 26th might be expected to have caused numerous seabed failures within the area of rupture that may have contributed to local tsunami runup. This contribution discusses the seabed morphology offshore of Sumatra acquired during the survey carried out by HMS Scott in January and February 2005. Utilising a unique high resolution 12 kHz, 361-beam hull-mounted Sass IV sonar, over 40,000 square kilometres of seabed were mapped. The objective was to identify seabed movements that were the result of the earthquake and to identify submarine slope failures that may have contributed to the tsunami. This paper reports on the results of the survey using Fledermaus imaging software. The area mapped is an accretionary complex formed as the two plates have converged over the past 40 million years. From the data several seabed failure mechanisms of different ages have been identified. Along the plate margin in the west of the survey area the deformation front comprises a series of young thrust folds up to 1000m in elevation and tens of kilometres in length. In places the seaward faces of these folds have failed cohesively and slumped blocks 100's of metres high and up to several kilometres long have been displaced up to 13 kilometres onto the inner trench floor. At other locations older episodes of failure are identified by the presence of displaced slumped blocks located on the crests of the folds; the slumps thus predating uplift. Where young thrust folds are absent, the outer margin of the accretionary prism is deeply dissected and comprises a steeply sloping seabed incised by numerous gullies and slide scars. Here, mechanisms of failure are incremental, and take place mainly through headwall erosion. There are small cohesive failures, although most sediment appears to be shed from the gullies onto the inner trench through channels incised into the seabed. Sediment overflow from the channels has resulted in the construction of sediment fans upon which are located giant sediment waves.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 3022 Marine sediments: processes and transport
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3070 Submarine landslides
DE: 9340 Indian Ocean
SC: Union [U]
MN: Fall Meeting 2005