Can Plate Bending Explain the Observed Faster Landward Motion of Lateral Regions of the Subduction Zone After Major Megathrust Earthquakes?

M. D’Acquisto*, M. W. Herman, R.E.M. Riva, R. Govers

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

Greater landward velocities were recorded after six 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. This conclusion does not significantly change when varying mantle viscosity, plate elasticity, maximum afterslip depth, earthquake size, megathrust locking outside of the rupture, or nature and location of relevant model boundaries. The observed ELM consequently appears to reflect faster slip deficit accumulation, implying a greater seismic hazard in lateral segments of the subduction zone.

Original languageEnglish
Article numbere2022JB025431
Number of pages21
JournalJournal of Geophysical Research: Solid Earth
Volume128
Issue number3
DOIs
Publication statusPublished - 2023

Keywords

  • earthquake cycle
  • enhanced landward motion
  • in-plane bending
  • megathrust
  • postseismic relaxation
  • surface velocities

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