Geological evidences of the fifth model for the tsunami generation in ocean floor off northwest Sumatra during the 2004 Sumatra-Andaman earthquake
Abstract
A common character among fault models proposed for the 2004 Mw 9.3 Sumatra-Andaman earthquake is large slip off northwest Sumatra, which is considered to be responsible for huge tsunami heights of more than 20 m on average, as measured in field surveys along the west coast of Aceh. However, the generation mechanism of the huge tsunami remains unresolved, although five hypothetical models have been proposed. Among them, the fifth hypothetical model was proposed by Hirata et al. [2008a, b] that the 2004 earthquake ruptured updip along the megathrust (plate interface) near the deformation front, but branched onto one of the outer-arc high splay faults: either the Middle Thrust or possibly the Lower Thrust of Sibuet et al.[2007]. To examine the fifth hypothetical model, we have conducted a multi-narrow beam swath bathymetry around the Middle Thrust and Lower Thrust within the well-developed outer-arc high region off northwest of Sumatra as a task of a scientific research cruise KY09-09 using the JAMSTEC R/V Kaiyo during a period from 26 October 2009 to 20 November 2009. After the KY09-09 cruise, we then merged the bathymetry data into that, previously obtained by the previous Japanese research cruise NT05-02, and finally produced a detailed bathymetry data with its grid spacing of 37 m, which is much finer than those (about 100 - 150 m spacing) previously obtained by other foreign cruises. In the survey area, the water depth ranges from 300 m to 3300 m. A prominent feature in the detailed bathymetry is a series of ridge and trough structure trending along the arc in the direction of NNW-SSE, parallel to the strike of the Sumatra Trench. In particular, we can identify a clearly distinguishable fault traces at around 50 km landward from the deformation front located in the toe of the accreationary prism. The fault traces cross, in turn from southeast to northwest, (a) the central axis of a NNW-SSE trending, narrow and long sedimentary trough in the southwest part of the region, (b) the base of the southwesterly dipping slope of a NNW-SSE striking, well-developed ridge, (c) two slope failures with the edges of the rims, which is seen the most sharpest and freshest in the region, on both of the southeastern side and northwestern side of a mountain-like structure, and (d) the eastern edge of a NNW-SSE trending, narrow and long sedimentary trough to the north of 4.5 degree N. We consider this clear fault traces with the two, perhaps fresh, slope failures as the Middle Thrust. Acknowledgements: We thank the Captain and crews of the R/V Kaiyo for their skillful operation during the KY09-09 cruise.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T11B2090H
- Keywords:
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- 3045 MARINE GEOLOGY AND GEOPHYSICS / Seafloor morphology;
- geology;
- and geophysics;
- 3070 MARINE GEOLOGY AND GEOPHYSICS / Submarine landslides;
- 3075 MARINE GEOLOGY AND GEOPHYSICS / Submarine tectonics and volcanism