Bathymetric survey images structure off Sumatra



Fault rupture models and aftershock activities of both the 26 December 2004 Mw 9.3 and the 28 March 2005 Mw 8.7 earthquakes postulate a strong structural segmentation of the Sumatra fore arc, or the region between a subduction trench and the volcanic arc. The 2004 earthquake rupture propagated some 1200–1400 kilometers to the northwest from the epicenter along the plate boundary Yet the rupture ended abruptly at a southern boundary crosscutting the upper plate from the trench to the island of Simeulue. Similarly, the rupture plane and aftershock distribution of the 2005 earthquake are confined to a zone some 300–400 kilometers around the epicenter off Nias Island, clearly distinguishable from the northern rupture zone.