Detailed seafloor morphology in the epicentral region of the Great Sumatra-Andaman earthquake from the compilation of 2005-2006 French and British swath bathymetric data
Abstract
The 26th December 2004 Great Sumatra Earthquake is the second largest earthquake (Mw=9.1) recorded during the past century. In order to investigate the sea-floor morphology and potentially recent fault activity related to the seismic activity, swath bathymetric mapping was conducted by the French vessel R/V Marion Dufresne during Sumatra-Aftershocks 2005 cruise and complemented during SAGER-OBS in 2006. The 2005 box was a 370 km x 75 km strip located between northern Sumatra and the Indonesia/India boundary (Sibuet et al, 2005). These data complemented the data acquired by HMS Scott (Henstock et al, 2006) earlier in 2005. This year, we filled the gap in the 2005 surveys and added two more boxes. Box A is located over the outer ridge and wedge, east of the area covered during the Sumatra Aftershocks cruise. Box B is in the vicinity of the epicentre and completes the existing data set on the outer ridge, north of the West Andaman Fault (WAF). These data, combined with the HMS Scott data represent about 70 percent of the surface area between west Simeulue Island and the India-Indonesia boundary, from the trench to north- west Sumatra. This dataset provides for the first time the detailed morphology of the vast epicentral region, which permits us to identify fine-scale as well large-scale geo-morphological features related to subduction processes. New data outline the major discontinuity of the deflection of the outer ridge where it crosses the WAF. As identified last year, some of the active deformation in the wedge and at the base of the outer ridge could be interpreted as the emergence of major splay faults that may accommodate part of the December 26th earthquake thrusting. Apart from thrusting, the upper part of the wedge shows folds and pull-apart basins that indicate a significant strike motion. To the south, the outer ridge is well developed in the continuity of Simeulue Island forming a 60 km wide, relatively smooth 1000 m deep plateau. The entire data-set outlines the narrowing of the wedge to the south and the evolution of the outer arc high bounding a nearly undeformed forearc basin domain, significantly less developed to the south in response to the evolution of the obliquity of the convergence. The data also confirms the important role of the WAF in this evolution as a major upper plate boundary. In conclusion, these bathymetric data, together with the 3.5 kHz data and deep seismic data will help to better determine the morpho-tectonic evolution of the Sumatra convergent margin from Indian waters to the west of Simeulue Island, an area which was strongly affected by the December 2004 earthquake.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.U53C..05G
- Keywords:
-
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413);
- 7240 Subduction zones (1207;
- 1219;
- 1240);
- 8104 Continental margins: convergent;
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413)