Using two-dimensional finite element modeling, we reproduced the observed postseismic deformation of the 2011 Tohoku-Oki earthquake. Our model, which accounts for the lithosphere-asthenosphere boundary and weak zones beneath volcanoes, was able to reproduce small-scale (<20 km) perturbations in postseismic deformation observed by the dense geodetic network, such as local subsidence around Quaternary volcanoes. The inverted afterslip has a peak at the downdip limit of the main rupture region on the subducting plate interface, consistent with physical predictions. The combination of afterslip and viscoelastic relaxation in a heterogeneous rheology model explains the observations well, even on small scales.