A secondary zone of surface uplift (SZU), located ~300 kilometers from the trench, has been measured after several megathrust earthquakes. The SZU reached a few centimeters hours after the 2011 Mw 9.1 Tohoku (Japan) earthquake. Less than a day after the 2010 Mw 8.8 Maule (Chile) earthquake, it peaked at 12 cm. Published coseismic finite-fault models for these events do not reproduce the measured SZU.
One interpretation is that this SZU is universal, driven by volume deformation around the slab interface (van Dinther et al. 2019). In contrast, with synthetic tests and an investigation of the Maule event, we demonstrate the SZU may instead result from slip on the slab interface. Further, we suggest that slip occurs as rapid postseismic afterslip. We can reproduce the SZU with fault slip if elastic heterogeneities associated with the subducting slab are accounted for, as opposed to assuming homogeneous or layered elastic lithospheric structures.