Overturning Nature of the Subducting Slab in the Andaman and Sumatra Subduction Zone: A Numerical Study using ASPECT

The Andaman and Sumatra subduction zone exhibits unique tectonic behavior, notably characterized by the overturning nature of the subducting slab, setting it apart from other subduction zones. This study investigates the complexities of this phenomenon using high-resolution numerical simulations conducted with the Advanced Solver for Problems in Earth's ConvecTion (ASPECT) software. The simulations, spanning a geological timescale of 15 million years, reveal intricate details about the dynamics of the subducting Indo-Australian plate. The relatively dense subducting slab, with a density of 3300 kg/m³, interacts with the curved and segmented geometry of the subduction zone, leading to distinct stress distributions and unique slab dynamics. The thermal structure, influenced by a serpentinized mantle wedge in the overriding plate with a lower density of 2950 kg/m³ and thermal conductivity of 1 W/m·K, further modifies the subduction process by altering the thermal gradient and buoyancy forces. The trench rollback rate of 5 cm/year, coupled with hydration, serpentinization, and viscosity variations (ranging from 1e20 to 1e22 Pa·s), plays a significant role in driving slab deformation and overturning. Ambient mantle flow, modeled with a gravitational force of 9.81 m/s², interacts with the subducting slab, generating torques and forces that contribute to its overturning behavior. The high-resolution capabilities of ASPECT enabled the capture of fine-scale features and long-term dynamics, offering valuable insights into the region's tectonic mechanisms. This study not only advances our understanding of the Andaman and Sumatra subduction zone but also holds significant implications for seismic hazard assessment and geodynamic research. Future work will incorporate three-dimensional models and explore additional factors such as fluid migration and mantle flow heterogeneities to further elucidate subduction dynamics.