** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its society members.
Gallery View of PEPS Articles
Review
Solid earth sciences
202307202307
Progress in modeling the Tohoku-oki megathrust earthquake cycle and associated crustal deformation processes
Bunichiro Shibazaki
2011 Tohoku-oki earthquake, Numerical modeling, Megathrust earthquake cycle, Hierarchical asperity model, Dynamic weakening, Postseismic deformation, Viscoelastic relaxation, Postseismic slip, Long-term vertical deformation
Examples of modeling of megathrust earthquake cycles and postseismic deformation for the 2011 Tohoku-oki earthquake and long-term vertical crustal deformation prior to the Tohoku-oki earthquake presented in this paper. (Left) Distribution of friction parameters used in the earthquake cycle model (Shibazaki et al. 2019), considering shallow fault friction properties obtained from JFAST. Regions, where a-b is negative, indicate asperities of velocity weakening. (Right top) Modeling of postseismic deformation (Agata et al. 2019). Total displacement of the crust and mantle and viscosity of the mantle 2.8 years after the Tohoku-oki earthquake. The Tohoku-oki earthquake caused large stress fluctuations, resulting in a sudden viscosity decrease and rapid flow in the asthenosphere below the oceanic lithosphere. (Right bottom) Modeling of vertical crustal deformation rates and motions in the island arc crust and mantle prior to the Tohoku-oki earthquake (Sasajima et al. 2019). The model reproduced the subsidence of the Pacific coast of northeast Japan observed for about 100 years prior to the Tohoku-oki earthquake.
This paper summarizes the results of 10 years of research on models of the megathrust earthquake cycles and crustal deformation associated with the 2011 Tohoku-oki earthquake. Several earthquake cycle models have been proposed for the northeast Japan subduction zone to elucidate why megathrust earthquakes occur at intervals of approximately 600 years and why large slips occurred in the shallow subduction zone. A model that considers a strong asperity in the shallow plate interface, and a hierarchical asperity model that considers the scale dependence of the critical displacement of the rate- and state-dependent friction law have been proposed. Modeling with dynamic weakening of faults has also been proposed. In the model using the shallow friction characteristics obtained by the Japan Trench Fast Drilling Project, rupture from depth can propagate to the trench, resulting in shallow large slips. Submarine crustal deformation has been observed for the first time in addition to dense observations of the inland crustal deformation. The observation of the seafloor deformation near the trench showed that viscoelastic relaxation played an important role in short-term postseismic deformation near the trench. The effects of the low-viscosity region at the oceanic lithosphere and asthenosphere boundary, and the cold forearc mantle wedge (cold nose) have been discussed. Simulations using the nonlinear flow law of rock in the mantle, where a power–law relationship holds between stress and strain rate, and the fault friction law at the plate boundary, show that the Tohoku-oki earthquake caused large stress fluctuations, resulting in a sudden viscosity decrease and rapid flow in the asthenosphere below the oceanic lithosphere. The simulations of the crustal deformation associated with the Tohoku-oki earthquake cycle also indicate that in the later stage of the earthquake cycle, the Pacific coastal region begins to subside due to the increasing slip deficit rate on the deeper parts of the plate interface. These results explain the subsidence of the Pacific coast of northeast Japan observed for about 100 years prior to the Tohoku-oki earthquake. In the future, a model that explains the long-term crust and mantle deformation during the entire Tohoku-oki earthquake cycle must be constructed.
