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Taking advantage of the increased ray coverage due to seismicity following the 2004 December and 2005 March great earthquakes, an improved iterative regional–global tomographic method was applied to the Sumatra–Andaman and adjacent regions to better constrain the 3-D mantle velocity heterogeneity in the region. Velocity and hypocentral parameters were iteratively perturbed to sharpen the image of the subducted slab. Several iterations were performed, and the effects of source mislocation were considered in the iterative process, an issue usually neglected in global tomography. We find that source relocation between iterations increases the amplitudes of slab anomalies and sharpens the definition of slab geometry beyond what can be achieved by a fixed-source iterative inversion alone. In addition, extensive restoration tests of synthetic data were conducted that emphasize enhancements obtained by our iterative process. These tests show significant increases in amplitude and decreased smearing of synthetic slab features. Thus, when applied to the real data, similar enhancements are inferred in the resulting model, which better illustrates the complex slab geometry in the upper-mantle and transition zone regions along the Sumatra, Andaman and Burma subduction zones. [ABSTRACT FROM AUTHOR]