Evaluating slab-plate coupling in the Indo-Australian plate

Distributed seismicity in the central Indian Ocean affords a unique opportunity to evaluate the extent of slab-plate coupling in the Indo-Australian plate. The mix of reverse-fault and strike-slip mechanisms in this region, with northwest-southeast to north-south maximum horizontal stress, S_Hmax, implies that the effective slab pull is no more than ∼10% of the total negative buoyancy operating on the subducting slab. Numerical models of the intraplate stress field predict a slab-pull component along the Sumatra and Java boundary segments of 2.82 ± 0.82 and 0.89 ± 0.35 × 10¹² N·m^-1, respectively. Mantle tomographic constraints coupled with insights from analogue modeling suggest that the differences relate to variations in the depth extent of the slabs and the degree of slab support provided by the transition zone. These results help resolve apparent contradictions between insights from intraplate stress fields and plate dynamics; i.e., although plate motion is dominated by subduction, slab pull is only poorly expressed in the intraplate stress field because of low slab-plate coupling.