Offshore Landward Motion Shortly After a Subduction Earthquake Implies Rapid Relocking of the Shallow Megathrust

Mario D’Acquisto; Rob Govers

doi:10.1029/2022GL101638

Offshore Landward Motion Shortly After a Subduction Earthquake Implies Rapid Relocking of the Shallow Megathrust

Mario D’Acquisto^*, Rob Govers

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Geodetic observations after large subduction earthquakes reflect multiple postseismic processes, including megathrust relocking. The timing of relocking and the observational constraints on it are unclear. Relocking was inferred to explain some observed landward motion that occurs within months. It was also considered unable to explain other, greater landward motion, including that off the coast of Japan beginning weeks after the 2011 Tohoku earthquake, attributed to postseismic relaxation. We use generic, 3D numerical models to show that relocking, particularly of the shallow interface, is needed for postseismic relaxation to produce landward motion on the tip of the overriding plate. We argue that this finding is consistent with previous simulations that implicitly relock the megathrust where afterslip is not included. We conclude that the Tohoku megathrust relocked within less than 2 months of the earthquake. This suggests that the shallow megathrust probably behaves as a true, unstably sliding asperity.

Original language	English
Article number	e2022GL101638
Pages (from-to)	1-10
Number of pages	10
Journal	Geophysical Research Letters
Volume	50
Issue number	1
DOIs	https://doi.org/10.1029/2022GL101638
Publication status	Published - 16 Jan 2023

Bibliographical note

Funding Information:
This work was partly funded by Dutch Research Council (NWO) Grant ALWGO.2017.007. The mesh generator program Gmsh (Geuzaine & Remacle, 2009) was used to make the finite element meshes for the numerical models. The Generic Mapping Tools (Wessel et al., 2019) and Adobe Illustrator were used for visualization.

Funding Information:
This work was partly funded by Dutch Research Council (NWO) Grant ALWGO.2017.007. The mesh generator program Gmsh (Geuzaine & Remacle, 2009 ) was used to make the finite element meshes for the numerical models. The Generic Mapping Tools (Wessel et al., 2019 ) and Adobe Illustrator were used for visualization.

Publisher Copyright:
© 2022. The Authors.

Funding

This work was partly funded by Dutch Research Council (NWO) Grant ALWGO.2017.007. The mesh generator program Gmsh (Geuzaine & Remacle, 2009) was used to make the finite element meshes for the numerical models. The Generic Mapping Tools (Wessel et al., 2019) and Adobe Illustrator were used for visualization. This work was partly funded by Dutch Research Council (NWO) Grant ALWGO.2017.007. The mesh generator program Gmsh (Geuzaine & Remacle, 2009 ) was used to make the finite element meshes for the numerical models. The Generic Mapping Tools (Wessel et al., 2019 ) and Adobe Illustrator were used for visualization.

Keywords

earthquake cycle
megathrust relocking
numerical modeling
offshore displacement
postseismic relaxation
surface velocities

Access to Document

10.1029/2022GL101638Licence: CC BY

Geophysical Research Letters - 2022 - D Acquisto - Offshore Landward Motion Shortly After a Subduction Earthquake ImpliesFinal published version, 3.35 MBLicence: CC BY

Cite this

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title = "Offshore Landward Motion Shortly After a Subduction Earthquake Implies Rapid Relocking of the Shallow Megathrust",

abstract = "Geodetic observations after large subduction earthquakes reflect multiple postseismic processes, including megathrust relocking. The timing of relocking and the observational constraints on it are unclear. Relocking was inferred to explain some observed landward motion that occurs within months. It was also considered unable to explain other, greater landward motion, including that off the coast of Japan beginning weeks after the 2011 Tohoku earthquake, attributed to postseismic relaxation. We use generic, 3D numerical models to show that relocking, particularly of the shallow interface, is needed for postseismic relaxation to produce landward motion on the tip of the overriding plate. We argue that this finding is consistent with previous simulations that implicitly relock the megathrust where afterslip is not included. We conclude that the Tohoku megathrust relocked within less than 2 months of the earthquake. This suggests that the shallow megathrust probably behaves as a true, unstably sliding asperity.",

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author = "Mario D{\textquoteright}Acquisto and Rob Govers",

note = "Funding Information: This work was partly funded by Dutch Research Council (NWO) Grant ALWGO.2017.007. The mesh generator program Gmsh (Geuzaine & Remacle, 2009) was used to make the finite element meshes for the numerical models. The Generic Mapping Tools (Wessel et al., 2019) and Adobe Illustrator were used for visualization. Funding Information: This work was partly funded by Dutch Research Council (NWO) Grant ALWGO.2017.007. The mesh generator program Gmsh (Geuzaine & Remacle, 2009 ) was used to make the finite element meshes for the numerical models. The Generic Mapping Tools (Wessel et al., 2019 ) and Adobe Illustrator were used for visualization. Publisher Copyright: {\textcopyright} 2022. The Authors.",

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N2 - Geodetic observations after large subduction earthquakes reflect multiple postseismic processes, including megathrust relocking. The timing of relocking and the observational constraints on it are unclear. Relocking was inferred to explain some observed landward motion that occurs within months. It was also considered unable to explain other, greater landward motion, including that off the coast of Japan beginning weeks after the 2011 Tohoku earthquake, attributed to postseismic relaxation. We use generic, 3D numerical models to show that relocking, particularly of the shallow interface, is needed for postseismic relaxation to produce landward motion on the tip of the overriding plate. We argue that this finding is consistent with previous simulations that implicitly relock the megathrust where afterslip is not included. We conclude that the Tohoku megathrust relocked within less than 2 months of the earthquake. This suggests that the shallow megathrust probably behaves as a true, unstably sliding asperity.

AB - Geodetic observations after large subduction earthquakes reflect multiple postseismic processes, including megathrust relocking. The timing of relocking and the observational constraints on it are unclear. Relocking was inferred to explain some observed landward motion that occurs within months. It was also considered unable to explain other, greater landward motion, including that off the coast of Japan beginning weeks after the 2011 Tohoku earthquake, attributed to postseismic relaxation. We use generic, 3D numerical models to show that relocking, particularly of the shallow interface, is needed for postseismic relaxation to produce landward motion on the tip of the overriding plate. We argue that this finding is consistent with previous simulations that implicitly relock the megathrust where afterslip is not included. We conclude that the Tohoku megathrust relocked within less than 2 months of the earthquake. This suggests that the shallow megathrust probably behaves as a true, unstably sliding asperity.

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Offshore Landward Motion Shortly After a Subduction Earthquake Implies Rapid Relocking of the Shallow Megathrust

Abstract

Bibliographical note

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Keywords

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