2008 Little Andaman aftershock: genetic linkages with the subducting 90°E ridge and 2004 Sumatra–Andaman earthquake

Abstract

We analyse the June 27, 2008 Little Andaman aftershock (Mw 6.6) of December 26, 2004 Sumatra–Andaman earthquake (Mw 9.2) that occurred near the trench in the subducting India plate beneath the Sunda Plate. Unlike majority of the other aftershocks in the frontal arc, the Little Andaman aftershock and its own aftershocks occurred through normal slip on the north–south oriented steep planes. We use the coseismic and ongoing postseismic deformation due to the 2004 Sumatra–Andaman earthquake at a GPS site nearest to the Little Andaman aftershock and compute changes in the Coulomb stresses due to the coseismic slip and postseismic afterslip. The Coulomb stress on the Little Andaman aftershock fault plane progressively increased since the 2004 Sumatra–Andaman earthquake which probably led to the occurrence of the Little Andaman aftershock on the pre-existing N–S oriented strike-slip steep planes of the subducting 90°E ridge that were reactivated through normal slip.