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

Mario D'Acquisto , Matthew W Herman, R.E.M. Riva, Rob Govers

Research output: Contribution to conferencePosterScientific


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.
Original languageEnglish
Number of pages1
Publication statusPublished - 2022
EventAGU Fall Meeting 2022 - Chicago, United States
Duration: 12 Dec 202216 Dec 2022


ConferenceAGU Fall Meeting 2022
Abbreviated titleAGU 2022
Country/TerritoryUnited States


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