Lithospheric Framework of Sumatra–Andaman Subduction Zone—A Review

Abstract

Sumatra–Andaman subduction zone, where the Indo-Australian plate subducts obliquely beneath Burmese–Sumatra plate, is one of the most seismically active zones and produced two great megathrust earthquakes (Mw 9.1, 2004 Sumatra and Mw 8.6, 2005 Nicobar) in the recent past. Our understanding of this subduction system is considerably advanced due to several studies carried out after the 2004 great Sumatra earthquake. This article presents an overview of the prominent results on lithospheric structure obtained from the analyses of seismological, gravity, geoid and other data sets. The geometry of subduction zone, structure of accretionary prism and Benioff zone show extensive diversity along the subduction axis viz: broad accretionary prism area in the central region (~ 0–10° N) compared to its north and south; variations in lithospheric thickness of Indo-Australian plate; steeper subducting slab in the Andaman region compared to the Sumatra; missing subducting slab in the northern Andaman region; trench parallel seismic anisotropy in Andaman-Nicobar in contrast to trench perpendicular in Sumatra region and deeper Moho under the Ninety-degree east (NER), Alcock Rise (AR) and Sewell Rise (SR). These observations suggest along axis variations in the subduction geometry, dynamics and their relations with earthquake rupture dynamics.