A secondary zone of uplift measured after megathrust earthquakes: caused
by early downdip afterslip?
Abstract
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.