Seismic evidence for broken oceanic crust in the 2004 Sumatra earthquake epicentral region

Singh, Satish C. and Carton, Helene and Tapponnier, Paul and Hananto, Nugroho D. and Chauhan, Ajay P. S. and Hartoyo, Djoko and Bayly, Martin and Moeljopranoto, Soelistijani and Bunting, Tim and Christie, Phil and Lubis, Hasbi and Martin, James (2008) Seismic evidence for broken oceanic crust in the 2004 Sumatra earthquake epicentral region. Nature Geoscience, 1 (11). pp. 777-781. ISSN 1752-0894 EISSN:1752-0908 DOI 10.1038/ngeo336

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Abstract

The great Sumatra earthquake of 26 December 2004 was the third largest event to occur in a subduction zone in the past 50 years. The rupture initiated at 30–40 km depth northwest of Simeulue Island1 and propagated for approx1,300 km to the northern Andaman Islands2. The earthquake was caused by sudden slip along the plate interface between the subducting Indo-Australian plate and the overriding Sunda plate3, 4. Although detailed knowledge of the structure of the subduction interface is important to define potential sources of large megathrust earthquakes, available data5, 6, 7, 8 have not provided such information so far. Here we present a high-quality seismic section of the focal region, from the abyssal plain down to 40 km depth below the fore-arc. The seismic data reveal that the subducting crust and oceanic Moho—the crust–mantle boundary—are broken and displaced by landward-dipping thrust ramps, suggesting that the megathrust now lies in the oceanic mantle. We image active thrust faults at the front of the accretionary wedge, consistent with thrust aftershocks on steeply dipping planes. Our observations imply that very strong coupling leading to brittle failure of mantle rocks accounts for the initiation of such an exceptionally large earthquake.

Item Type: Article
Uncontrolled Keywords: 2008AREP;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Nature Geoscience
Volume: 1
Page Range: pp. 777-781
Identification Number: 10.1038/ngeo336
Depositing User: Sarah Humbert
Date Deposited: 15 Dec 2011 17:24
Last Modified: 23 Jul 2013 10:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/2282

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