Complex slab subduction beneath northern Sumatra

Abstract

New data provided by the 2004-2005 Sumatra-Andaman great earthquake sequences allow us to image with improved detail the P-wave velocity structure beneath Sumatra and adjacent regions. Below northern Sumatra, we find that the slab is folded at depth, exhibiting geometry similar to that of the volcanic arc and the trench at the surface. We speculate that this fold plays a major role in the segmentation of the Sumatra megathrust, and may impede rapture propagation in the region. North of Sumatra, significant slab material in the mantle transition zone is imaged for the first time, and we infer the presence of a major tear between the upper mantle and transition zone there. Copyright 2008 by the American Geophysical Union.