HR: 0800h
AN: S31C-0563    [Abstracts]
TI: Seismic Evidence for a Mantle Megathrust Producing the Giant Sumatra-Andaman Earthquake
AU: Bayly, M
EM: mbayly@perth.westerngeco.sl.com
AF: WesternGeco, St George terrace, Perth, WA 6000, Austria
AU: * Singh, S C
EM: singh@ipgp.jussieu.fr
AF: Institut de Physique du Globe de paris, 4 place Jussieu, Paris cedex 05, 75252, France
AU: Carton, H
EM: carton@ipgp.jussieu.fr
AF: Institut de Physique du Globe de paris, 4 place Jussieu, Paris cedex 05, 75252, France
AU: Tapponnier, P
EM: tappon@ipgp.jussieu.fr
AF: Institut de Physique du Globe de paris, 4 place Jussieu, Paris cedex 05, 75252, France
AU: Hananto, N
EM: hananto@ipgp.jussieu.fr
AF: Institut de Physique du Globe de paris, 4 place Jussieu, Paris cedex 05, 75252, France
AU: Chauhan, A
EM: chauhan@ipgp.jussiu.fr
AF: Institut de Physique du Globe de paris, 4 place Jussieu, Paris cedex 05, 75252, France
AU: Hartoyo, D
EM: djoko@webmail.bppt.go.id
AF: BPPT, Thamrin 8, Jakarta, 10340, Indonesia
AU: Moeljopranoto, S
EM: lies@jakarta.westerngeco.slb.com
AF: Westerngeco, Rasuna Said Kav, Jakarta, 12940, Indonesia
AU: Bunting, T
EM: TBunting@kuala-lumpur.westerngeco.slb.com
AF: WesternGeco, Jalan Perak, Kuala Lumpur, 50450, Malaysia
AB: The great (M = 9.3) Sumatra-Andaman earthquake of 26 December 2004 was the third largest subduction event in the last 50 years. The rupture initiated at 30-40 km depth northwest of Simeulue Island and propagated as far as the northern Andaman Islands, breaking a total area of about 1300 x 150 km2. The earthquake was caused by a sudden slip -up to 30 m - releasing stress accumulated for many hundreds of years on an interface (megathrust) along which the Indo-Australian plate subducts beneath Sunda and Burma plates. Using high- resolution deep seismic reflection imaging, we show that the subducting oceanic crust and Moho are sliced by at least six NE dipping thrust faults that may have their roots in the oceanic mantle, requiring the presence of a megathrust in the mantle. Near the subduction front, these deep-rooted faults continue in the overlying sediments and are associated with seafloor scarps and steep slopes, suggesting that these faults are active and extend to the seafloor. The presence of steeply dipping thrust earthquakes near the subduction front, some of which are in the down-going plate, further corroborates these observations. Beneath the forearc basin, aftershocks lie below the imaged basalt-sediment interface, confirming the presence of active thrust in the down-going plate. We also observed a reflective zone just above the plate interface, which might be a slice of unerplatted oceanic crust. Taken together, these results imply that very strong coupling, appropriate for brittle failure of mantle rocks, accounts for the initiation of such an unusually powerful tsunamigenic event. A megathrust in the mantle would increase the width of seismogenic zone both towards up dip and down dip. Perhaps the 2004 Sumatran event should be considered an example of a novel class of exceptionally large and infrequent megathrust earthquakes ("Mantle Megaquakes": Mw: 9-10), typical of subduction zones and great collision ranges such as the Himalayas, rupturing deep mantle interfaces with a mechanical strength much greater than that of thrusts in the crust.
DE: 1209 Tectonic deformation (6924)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting