HR: 14:55h
AN: S23D-06    [Abstracts]
TI: Crustal structure of the 2004 Great Sumatra Earthquake epicentral zone from wide-angle seismic data.
AU: * Klingelhoefer, F
EM: fklingel@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29280, France
AU: Dessa, J
EM: dessa@geoazur.obs-vlfr.fr
AF: Geosciences Azur, BP 48, Villefranche sur Mer, 06235, France
AU: Graindorge, D
EM: David.Graindorge@univ-brest.fr
AF: University Brest, Place Nicolas Copernic, Plouzane, 29280, France
AU: Gutscher, M
EM: gutscher@univ-brest.fr
AF: University Brest, Place Nicolas Copernic, Plouzane, 29280, France
AU: Permana, H
AF: LIPI, Jl. Sangkuriang, Bandung, 40132, Indonesia
AU: Andre, C
EM: kamilh.andre@wanadoo.fr
AF: University Brest, Place Nicolas Copernic, Plouzane, 29280, France
AU: Dean, S
EM: smd9@noc.soton.ac.uk
AF: NOC, European Way, Southampton, SO14 3ZH, United Kingdom
AU: Singh, S
EM: singh@ipgp.jussieu.fr
AF: IPGP, 4 Place Jussieu, Paris, 75252, France
AU: Chauhan, A
EM: chauhan@ipgp.jussieu.fr
AF: IPGP, 4 Place Jussieu, Paris, 75252, France
AB: The 26th December 2004 great Sumatra earthquake (Mw=9.1) is among the 4 largest earthquakes ever recorded and the largest of the last 40 years. It initiated at a depth of 20-30 km and ruptured about 1300 km of the Indo-Australian/Sunda plate boundary, from the vicinity of Simeulue Island up to the north of Andaman Islands. During the SAGER-OBS cruise 56 ocean-bottom seismometers were deployed on a profile which crosses the margin north of Simeulue Island, in the epicentral area. The profile is 252 km-long, resulting in a 4.6 km instrument interval. A seismic refraction source of 8,300 in3 was used to fire 2170 shots on the profile. Data quality is excellent with useful arrivals to distances up to 180 km from the shot position. A tomographic inversion of 33127 picked first arrivals allows first insights into the deep structure of the zone of origin of the great earthquake. The subducting oceanic slab can be imaged down to a depth of ~25 km, more than 100 km landward from the trench. Based on seismic velocities, there is no evidence of a crystalline backstop up to ~120 km from the trench axis, below the fore arc basin. This implies that a significant part of the seismogenic interplate would consist of a contact between ancient accreted sediments and the downgoing plate. A high velocity zone at the lower landward limit of the ray-covered domain, at ~23 km depth, may indicate a shallow continental Moho. This observation might imply that the 2004 megathrust earthquake nucleated on a portion of the plate contact that lies between the upper surface of the downgoing plate and the fore arc mantle. At the seaward end of the model, 4-5 km of sediments seem to overlie the oceanic crust at the trench, most likely consisting of trench fill and older hemi-pelagic sediments.
DE: 3025 Marine seismics (0935, 7294)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Seismology [S]
MN: 2007 Fall Meeting