Letter abstract
Nature Geoscience 1, 777 - 781 (2008)
Published online: 26 October 2008 | doi:10.1038/ngeo336
Subject Categories: Seismology | Structural geology, tectonics and geodynamics
Seismic evidence for broken oceanic crust in the 2004 Sumatra earthquake epicentral region
Satish C. Singh1, Hélène Carton1, Paul Tapponnier2, Nugroho D. Hananto1, Ajay P. S. Chauhan1, Djoko Hartoyo3, Martin Bayly4, Soelistijani Moeljopranoto5, Tim Bunting6, Phil Christie7, Hasbi Lubis8 & James Martin8
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 
1,300 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.
- Equipe de Géosciences Marines, Institut de Physique du Globe de Paris, 4 place Jussieu, 75252 Paris Cedex 05, France
- Equipe de Tectonique et Mécanique de la lithosphère, Institut de Physique du Globe de Paris, 4 place Jussieu, 75252 Paris Cedex 05, France
- Agency for the Assessment and Application of Technology (BPPT), Jl. MH Thamrin 8, Jakarta 10340, Indonesia
- WesternGeco ASA Region, Capital Centre, No. 256 St George Terrace, Perth, WA 6000, Australia
- WesternGeco, Sentra Mulia, Jl. H.R. Rasuna Said Kav. X-6 No.8, Jakarta 12940, Indonesia
- WesternGeco, Rohas Perkasa No. 8 Jalan Perak, Kuala-Lumpur 50450, Malaysia
- Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 OEL, UK
- WesternGeco, Gatwick Airport, RH6 0NZ, UK
Correspondence to: Satish C. Singh1 e-mail: singh@ipgp.jussieu.fr
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