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Seaward-concave subduction forearcs are controversial settings that exhibit remarkable along-strike variations of surface uplift and rock exhumation, the causes of which are still a matter of debate. While short-term (10-10^2 a) forearc uplift relates to locking of the megathrust, it is unclear which mechanism produces long-term (10^4-10^6 a) permanent surface uplift. In this work we use Coulomb-wedge solutions and background forearc seismicity (not megathrust) in order to investigate permanent deformation of the overriding plate in Peru-Chile and northern Japan. According to the Coulomb-wedge theory, the observed along-strike variations of long-term forearc uplift may reflect changes of (i) slab dip angle, (ii) wedge material strength and/or (iii) plate interface friction. Here, we explore the latter hypothesis through a comparison of the spatial distribution of basal friction (inferred from the taper geometry) and the pattern of background forearc seismicity (obtained from the International Seismological Center global earthquake catalog).In Peru-Chile, concordant patterns of cumulative seismic moment and inferred basal strength suggest that (i) at the curvature apex, low interplate friction is needed to explain the forearc morphology; (ii) permanent vertical displacement of the proximal wedge is likely accomplished through repeated non-megathrust seismic events; (iii) the wedge is largely in equilibrium. Conversely, in northern Japan a complex relationship between long-term deformation and plate-interface processes is deduced. [ABSTRACT FROM AUTHOR]