Impact of lower plate structure on upper plate deformation at the NW Sumatran convergent margin from seafloor morphology

Graindorge, David and Klingelhoefer, Frauke and Sibuet, Jean-Claude and McNeill, Lisa and Henstock, Timothy J. and Dean, Simon and Gutscher, Marc-André and Dessa, Jean Xaver and Permana, Haryadi and Singh, Satish C. and Leau, Hélène and White, N. J. and Carton, Hélène and Malod, Jacques André and Rangin, Claude and Aryawan, Ketut G. and Chaubey, Anil Kumar and Chauhan, Ajay and Galih, Dodi R. and Greenroyd, Christopher James and Laesanpura, Agus and Prihantono, Joko and Royle, Gillian and Shankar, Uma (2008) Impact of lower plate structure on upper plate deformation at the NW Sumatran convergent margin from seafloor morphology. Earth and Planetary Science Letters, 275 (3-4). pp. 201-210. ISSN 0012-821X DOI

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We present results from multibeam bathymetric data acquired during 2005 and 2006, in the region of maximum slip of the 26 Dec. 2004 earthquake (Mw 9.2). These data provide high-resolution images of seafloor morphology of the entire NW Sumatra forearc from the Sunda trench to the submarine volcanic arc just north of Sumatra. A slope gradient analysis of the combined dataset accurately highlights those portions of the seafloor shaped by active tectonic, depositional and/or erosional processes. The greatest slope gradients are located in the frontal 30 km of the forearc, at the toe of the accretionary wedge. This suggests that long-term deformation rates are highest here and that probably only minor amounts of slip are accommodated by other thrust faults further landward. Obvious N-S oriented lineaments observed on the incoming oceanic plate are aligned sub-parallel to the fracture zones associated with the Wharton fossil spreading center. Active strike-slip motion is suggested by recent deformation with up to 20-30 m of vertical offset. The intersection of these N-S elongated bathymetric scarps with the accretionary wedge partly controls the geometry of thrust anticlines and the location of erosional features (e.g. slide scars, canyons) at the wedge toe. Our interpretation suggests that these N-S lineaments have a significant impact on the oceanic plate, the toe of the wedge and further landward in the wedge. Finally, the bathymetric data indicate that folding at the front of the accretionary wedge occurs primarily along landward-vergent (seaward-dipping) thrusts, an unusual style in accretionary wedges worldwide. The N-S elongated lineaments locally act as boundaries between zones with predominant seaward versus landward vergence.

Item Type: Article
Uncontrolled Keywords: 08AREP; IA57;
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 275
Page Range: pp. 201-210
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 02 Jun 2009 16:19
Last Modified: 23 Jul 2013 09:55

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