Outer-rise stress regime post 2004 mega-thrust rupture: Constraints from source process of selected Sumatra – Andaman outer-rise earthquakes.

Abstract:

The outer-rise region of a subducting margin will be in a compressional state prior to a megathrust event and in a tensional state afterwards due to the large co-seismic displacements. In coupled subduction zones, tensional earthquakes are occasionally observed post a megathrust rupture, as tensional stress from slab pull is temporarily transmitted to the outer-rise. In this study we analyze some of the significant outer-rise events along the Sumatra-Andaman margin post 26 December 2004 Sumatra-Andaman earthquake, like those occurred on January 2005 (Mw=6.5), July 2005 (Mw=7.1), August 2009 (Mw=7.5 ), March 2010 (Mw=6.6) and June 2010 (Mw=7.5). We will be discussing the source parameters,kinematic rupture process, directivity and the average stress drop of these events which are derived using seismic body wave inversion. We adopted teleseismic body wave inversion methodology of Kikuchi and Kanamori (1982, 1986 and 1991). We will be discussing the stress drop patterns and a possible asperity model for this margin and compare with other major outer-rise events post Tohoku-Oki (2011) and Maule (2010) events. The stress regimes inferred from the P & T axis orientations and its temporal evolution from inter-seismic to post-seismic phase also will be discussed.