A Secondary Zone of Uplift Measured After Megathrust Earthquakes: Caused by Early Downdip Afterslip?

Abstract

A secondary zone of surface uplift (SZU), located from 200 to 400 km landward of the trench, has been measured after several megathrust earthquakes. The SZU reached a few centimeters hours to days after the 2011 Mw 9.1 Tohoku (Japan) and 2010 Mw 8.8 Maule (Chile) earthquakes. 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, https://doi.org/10.1007/s00024-019-02250-z). In contrast, we demonstrate the SZU may instead result from slip on the slab interface, and suggest it might be caused by rapid 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.