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 ∼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.
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Acknowledgements
We thank Schlumberger for its overall support and contribution to this project, and in particular, we recognize the efforts made by the captain and crew of the WesternGeco Q-Marine vessel, Geco Searcher. J.-P. Montagner and J. Ludden provided constant support for the Sumatra–Andaman Great Earthquake Research (SAGER) initiative. Agence National de la Recherche (France) and IPG Paris financially supported the participation of scientists in the survey. This is a collaborative project between the Government of Indonesia (BPPT & LIPI), Schlumberger (WesternGeco) and the Institut de Physique du Globe (IPG) de Paris. We thank R. Engdahl for providing aftershock relocations. Comments by D. Scholl helped improve the manuscript. This is IPGP contribution number 2432.
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Singh, S., Carton, H., Tapponnier, P. et al. Seismic evidence for broken oceanic crust in the 2004 Sumatra earthquake epicentral region. Nature Geosci 1, 777–781 (2008). https://doi.org/10.1038/ngeo336
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DOI: https://doi.org/10.1038/ngeo336
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