HMS Scott survey of Sumatra subduction zone

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).

Image of HMS Scott bathymetry

Above: Bathymetry collected by HMS Scott, illuminated from direction 225.
Dashed lines show the approximate rupture areas and small circles aftershocks
within the first two weeks following the 26 December 2004 (red) and 29 March 2005 (orange) earthquakes.

Key findings

Important results of the survey were as follows:

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.

Please contact us for reprints.

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.

Acknowledgements

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.