Contribution of background seismicity to forearc uplift

Rock exhumation and surface uplift over subduction zones require part of the stresses to cause crustal thickening within the wedge and/or through basal accretion. Although accumulated elastic strain around subduction zones is released through megathrust earthquakes and related aftershocks, these large events often result in no permanent forearc surface uplift. Nevertheless, energy is also released by more frequent and dispersed background seismicity, a signal that is often overlooked. Here we investigate the variability of this energy along the Peru–Chile and Japan margins. We find that the pattern of background seismicity correlates with the margin-parallel long-wavelength wedge geometry and with published estimates of geologic-timescale coastal uplift. Furthermore, the orientation of the principal stresses related to these background events is consistent with contractional seismicity, predominantly located at the deep (30–60 km) plate interface depth. Taken together, these results indicate that background seismicity is associated with crustal thickening during the megathrust interseismic period. This mechanism may contribute substantially to the surface uplift of subduction margins over geologic timescales. Frequent and dispersed small earthquakes may contribute substantially to uplift of subduction margins, according to an analysis of such seismicity in the Peru–Chile and Japan margins.