On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake

Poster (2022)

Authors

Mario D'Acquisto Universiteit Utrecht
Matthew Herman Universiteit Utrecht, California State University
R.E.M. Riva Physical and Space Geodesy - CEG
Rob Govers Universiteit Utrecht
Research Group
Atmospheric Remote Sensing (CEG) (TU Delft)
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Published Date

2022

Language

English

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Faculty

Civil Engineering & Geosciences

Department

Geoscience and Remote Sensing

Research Group

Atmospheric Remote Sensing

Abstract

Greater landward velocities were recorded after 6 megathrust earthquakes
in subduction zone regions adjacent to the ruptured portion. Previous
explanations invoked either increased slip deficit accumulation or plate
bending during postseismic relaxation, with different implications for
seismic hazard. We investigate whether bending can be expected to
reproduce this observed enhanced landward motion (ELM). We use 3D
quasi-dynamic finite element models with periodic earthquakes. We find
that afterslip downdip of the brittle megathrust exclusively produces
enhanced trenchward surface motion in the overriding plate. Viscous
relaxation produces ELM when a depth limit is imposed on afterslip. This
landward motion results primarily from in-plane elastic bending of the
overriding plate due to trenchward viscous flow in the mantle wedge near
the rupture. Modeled ELM is, however, incompatible with the
observations, which are an order of magnitude greater and last longer
after the earthquake. Varying mantle viscosity, plate elasticity,
maximum afterslip depth, earthquake size, and megathrust locking outside
of the rupture does not significantly change this conclusion. The
observed ELM consequently appears to reflect faster slip deficit
accumulation, implying a greater seismic hazard in lateral segments of
the subduction zone.