Landward flow in the upper mantle: effects of the heat sink and viscous coupling of the sinking slab

Regional studies landward of the trench show that gravity anomalies are low compared with those expected from the cold sinking slab and that residual depth anomalies are strongly negative at distances up to 1200 km from the trench. It is shown that flow models taking simultaneously account of the viscous coupling and of the cooling effect of the sinking slab are able to explain these facts: the viscous coupling being related only to observed data down to 400 km from the trench, while the cooling effect mainly explains data at larger distances from the subduction zone.