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TitleNew megathrust locking model for the southern Kurile Subduction Zone incorporating viscoelastic relaxation and non-uniform compliance of upper plate
AuthorItoh, YORCID logo; Nishimura, TORCID logo; Wang, KORCID logo; He, J
SourceJournal of Geophysical Research, Solid Earth vol. 126, issue 5, e2020JB019981, 2021 p. 1-16,
Alt SeriesNatural Resources Canada, Contribution Series 20200526
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf; html
AreaHokkaido; Tohoku; Pacific Ocean; Japan
Lat/Long WENS 139.0000 149.0000 46.0000 38.0000
Subjectstectonics; structural geology; geophysics; Nature and Environment; Science and Technology; Health and Safety; earthquakes; tectonic models; tectonic interpretations; subduction zones; plate margins; deformation; creep; crustal structure; mantle; satellite geodesy; navigation satellites; modelling; stress analyses; stress patterns; rheology; trenches; Kurile Subduction Zone; global navigation satellite systems (GNSS)
Illustrationslocation maps; geoscientific sketch maps; models; schematic cross-sections; tables; profiles
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2021 04 21
AbstractDense Global Navigation Satellite System (GNSS) observations enable the development of megathrust interseismic locking models for the southern Kurile subduction zone where many great earthquakes have occurred. Inversion of these data assuming uniform elastic Earth has yielded slip deficit rates that are unreasonably high and/or full locking depth that is unreasonably large. Using the finite element method, here we construct a new Kurile locking model that includes interseismic viscoelastic stress relaxation and non-uniform compliance of the elastic upper plate. Inverting the same geodetic data using the new subduction zone model alleviates the previously seen unreasonable features in inferred megathrust locking state. In the new model, full locking extends to shallower depths than the downdip limit of some large megathrust earthquakes including the 2003 Mw 8.0 Tokachi-oki earthquake, supporting the notion of the shrinking of the locked area before the earthquakes and/or propagation of seismic rupture into creeping areas as previously predicted by friction or dynamic rupture models. By modeling the effects of a few recent M 8 earthquakes, we show that postseismic transients of recent earthquakes, although second-order, should be addressed in deriving megathrust locking models. The locking state near the trench cannot be resolved by the land-based GNSS data regardless of the improved model rheology and structure, although independent observations, such as slow earthquakes, may be used to speculate on the near-trench locking state in various part of the margin in the absence of seafloor geodetic observations.
Summary(Plain Language Summary, not published)
Accurately estimating the locking state of a subduction megathrust from contemporary geodetic observations is important to understanding the risk of earthquakes and tsunamis faced by the coastal population. But the estimates are hampered by other processes that affect the geodetic data. In this paper, we explain how a better understanding of the upper plate structure can improve these estimates. In particular, the volcanic arc area and the back arc area are more compliant and exhibit faster shortening in response to megathrust locking. Knowledge of the greater compliance of these areas, together with the use of an Earth model that accounts for the viscous behaviour of the mantle as opposed to a purely elastic model, has enabled an improved megathrust locking model for the Kuril subduction zone in Japan. This case study has implication to other subduction zones such as Cascadia in North America.

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