Andaman-Nicobar-Sumatra subduction zone: Morphological and mechanical segmentation from high-resolution multibeam bathymetry

The Andaman-Nicobar-Sumatra subduction zone displays exceptional along-strike variability in forearc morphology and deformation style linked to changes in plate convergence, sediment input, and subducting-plate relief. This study presents the first contiguous, high-resolution multibeam bathymetry compilation of the Andaman-Nicobar-Sumatra accretionary prism (~197,500 km²), integrated with multichannel seismic reflection data to resolve along-strike morphotectonic segmentation at hazard-relevant scales. The dataset encompasses the rupture zone of the 2004 Sumatra megathrust earthquake, enabling a segment-scale morphotectonic synthesis, correlation between surface morphology, and rupture behaviour. The accretionary prism is segmented into four along-strike domains based on distinct structural characteristics. Each domain exhibits systematic variations in wedge geometry, ridge continuity, the dominant wavelength of the imbricate thrust fold, and the vergence of the frontal-thrust. Toward north, the Andaman frontal wedge is narrow and steep, and is characterized by seaward-vergent faulting, short-wavelength folding, and segmented ridge patterns, indicative of strong basal coupling and localized deformation consistent with a near-critical wedge state. The Andaman-Nicobar transition zone shows alternating seaward and landward-vergent structures and pop-up geometries, and disrupted ridge continuity with comparatively short-wavelength, interpreted as a kinematic pivot influenced by the subducting Ninety-East Ridge, marking a transition to a near-critical state. Southward, Nicobar frontal wedge is broader and characterized by arcuate outer ridges and landward-vergent frontal thrusts, long wavelength folding, and continuous ridge-trough systems, reflecting enhanced internal deformation and an undercritical state. The Sumatra segment culminates in a wide, low-relief outer wedge with continuous ridge-trough trains and sustained frontal accretion over a shallow decollement, consistent with a subcritical to undercritical state. Together, these segment-specific structural, morphologic and mechanical variations along the Andaman-Nicobar-Sumatra subduction front highlight how forearc morphology and wedge architecture modulate rupture propagation characteristics during 2004 great megathrust earthquake.