by Anil Earnest, T. C. Sunilkumar and K. Silpa
Differing views on the north-eastern Indian plate subduction and its seismic potential place the subduction process as relict, ceased, creeping, or fully locked, challenging the seismic hazard uncertainty estimates of Indo-Burmese Arc (IBA) at either extreme. To clear some of these contentions, we re-examine the state of the IBA stress field using available earthquake faulting mechanism solutions. Our stress inversion results underline the tectonic complexity and emphasize that the stress of this subduction is primarily driven by the northward oblique motion of the Indian Plate. Models highlight the presence of the least compressive stresses as the margin-normal component, all along the shallow sinking slab. Furthermore, solutions link the shallow strike-slip earthquakes with the lateral slab shear due to oblique slip-partitioning. Spatial variations in the Indian slab stress field indicate higher margin parallel compression at the Naga versus the Chin and Rakhine-Arakan segments, implying resistance to the northward motion of India, illuminating the buttressing effects on the IBA. Models also depict active shortening across the Kabaw Fault. Inversion solutions bring out a higher compressional environment toward the south, along the Sagaing Fault. Finally, based on the overall stress field variations, we speculate that the Rakhine-Bangladesh Megathrust could be a low-stress forearc, as across the arc interacting stress fields are weak, capable of generating megathrust ruptures. Being weak, the stress replenishment times could be longer than the mechanically strong subduction zones. Due to the spatial stress field variations and buttressing effects, the interface may exhibit a variable rupture mode.