During January and February, 2005, the Royal Navy survey vessel HMS Scott conducted bathymetric mapping of part of the Sumatra subduction zone. The work concentrated on the southern 450km of the 2004 rupture (within Indonesian waters) and on the deeper water around the trench and the slope of the accretionary wedge, although some coverage of the Aceh forearc basin was also obtained (see below for coverage map).
Important results of the survey were as follows:
1. The combination of regional coverage but high-resolution data allows us to study processes at a wide range of scales
2. Two main morphologies are present: (1) where folds at the front of the accretionary wedge are clear and undegraded, (2) where the entire lower wedge is eroded.
3. Where they are present, the frontal thrust folds are clear over lengths of 20-80km, and segmentation in these accommodates a change in the trend of the plate boundary.
4. Most of the folds are strongly asymmetric with a shallow slope to the seaward side, strongly implying that the fault beneath them dips to seaward (landward vergence).
5. Small (10-100m in elevation) tectonic features are widespread near the deformation front, seaward of the frontal folds. Their location suggests that they represent rupture to the seafloor during major plate boundary earthquakes.
6. Erosion of the accretionary wedge is pervasive.
7. Coherent landslides do occur at the deformation front, but are not common (only 6 are clearly identifiable within the survey, and most of these must be older than about 10000 years).
A paper on our interpretation of the data has been published and it would be appropriate to cite that if you make use of the data: TJ Henstock, LC McNeill, and DR Tappin, Seafloor morphology of the Sumatra subduction zone: Surface rupture during megathrust earthquakes? Geology, v34, pp485-488, 2006.
Abstract: High-resolution multibeam bathymetry data from the Sumatran subduction zone reveal the regional and local morphology, including small-scale fault-related features and landslides that may be linked to earthquakes in the recent geological past. The accretionary prism is steeply sloped and pervasively eroded, with evidence of unusual landward vergence (seaward fault dip) of the frontal thrusts. Small-scale (5-100 m height) fault scarps, folds, and troughs are common along the seaward edge of the frontal thrust at the deformation front. A model of back-thrust fault slip or bending moment folding during plate-boundary slip, such as during the 2004 M9.2 megathrust earthquake, can explain the position of these features on the seaward fold limb of a seaward-dipping thrust. We infer that in major Sumatran (and other similar settings) plate-boundary earthquakes, coseismic surface rupture may occur at the prism toe.
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The data are made available to download on behalf of the United Kingdom Royal Navy and UK Hydrographic Office on our ftp site. Please see the file readme.txt for information about the data structure and formats.
Data were gathered by HMS Scott, a UK Royal Navy Survey vessel during Marine Scientific Research coordinated by the Joint Environment directorate of Defence Intelligence. The Royal Navy, British Geological Survey, Southampton Oceanography Centre, UK Hydrographic Office and the Government of Indonesia cooperated on this project.