Weaddresstheroleoftheconcaveandconvexarcs(asobservedfromthesubductingplate)onthedeformationoccurringalongtheMyanmar-Andaman-Sumatramargin.Wecategorizethepre-andpost-seismicdeformationsofthelithosphereusingearthquakedatabaseoccurringeitherpriorto26thDecember2004M_w9.3off-Sumatramega-eventoraftertheincidence.Analysisunderpre-seismicdomainshowsthatareanearSumatrarecordshighestseismicity,whichlargelydropsintheareapasttheNorthAndaman,andfurtherincreasestowardsnorth.Shallowestdepthandminimumdipofthesubductinglithosphereisrecordedatthecentralsegmentwherethearctransformedintoconcaveshape.TheannualmomentenergyreleaseduringearthquakedecreasestomorethantwoordersofmagnitudepasttheNorthAndamantowardsnorthunderpost-seismicdeformationphase.HigherdepthsofcontinuityofeventsarepresumablyassociatedwithmoredippingBenioffzonesinboththeIndo-MyanmarandAndaman-Nicobarconvexarcs.Theseobservationsobviouslyaccountfortectonicsubpisionofthemarginnearconcaveshapearcaroundthecentralpart.Absenceofvolcanism,presenceofsplayfaultsintheback-arc,sharpreductioninseismicitynearcentralsegmentareinterpretedtobecausedbymajortectonicimpactoftheNNE-wardconvergingbuoyantNinety-eastRidgeagainsttheAsianPlate.Shallowestdip,smallelasticthickness,weakconvergingIndianlithosphere,andevidencesofseriesofen-echelonblocksofftheeasternsideofthebrokennorthernNinetyeastRidgemightbeincapableofgeneratinggreatearthquakeinthisarea.
