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Megathrust earthquakes can nucleate in the forearc mantle: Evidence from the 2004 Sumatra event

J.-X. Dessa 1 F. Klingelhoefer 2 David Graindorge 3, 4 Camille André 3, 4 H. Permana 5 Marc-André Gutscher 3, 4 A. Chauhan 6 S. C. Singh 6 The Sumatra-Obs Scieic Team
1 GEOAZUR 6526 - Géoazur
2 IFREMER Centre de Bretagne - Institut Français de Recherche pour l'Exploitation de la Mer - Brest
3 LDO - Domaines Océaniques
4 UEB - Université européenne de Bretagne - European University of Brittany
5 LIPI - Research Center for Geotechnology
6 IPGP - Institut de Physique du Globe de Paris
Abstract : Current models predict that the seismogenic zone along subduction thrusts, where the largest earthquakes nucleate and propagate, does not extend to the forearc mantle below the crust of the upper plate. Stable sliding conditions have been shown to prevail there, particularly along several circum-Pacific margins that underwent great megathrust earthquakes (Mw > 8.5) during the twentieth century. Based on geophysical investigation, we show that the great 2004 Sumatra-Andaman earthquake (Mw = 9–9.3) contradicts these models: not only did it propagate downdip along the interface between the forearc mantle and the subducting plate, but it actually nucleated along this reportedly aseismic part of the interplate contact. Petrological models can therefore underestimate the downdip extent of rupture zones to be expected in megathrust earthquakes, and need to be revised to account for this observation, albeit unusual.
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Submitted on : Friday, July 17, 2009 - 10:11:03 AM
Last modification on : Wednesday, June 30, 2021 - 9:40:06 PM

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INSU | UNICE | CNRS | UNIV-PARIS7 | IPGP | UNIV-BREST | OCA | GEOAZUR | UPMC | USPC | LGO | CMM | UNIV-COTEDAZUR | SORBONNE-UNIVERSITE | UNIV-PARIS | AFRIQ

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J.-X. Dessa, F. Klingelhoefer, David Graindorge, Camille André, H. Permana, et al.. Megathrust earthquakes can nucleate in the forearc mantle: Evidence from the 2004 Sumatra event. Geology, Geological Society of America, 2009, 37 (7), pp.659-662. ⟨10.1130/G25653A.1⟩. ⟨insu-00404745⟩

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