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[SCG40-23] Multi-scale circular patch model in quasi-dynamic numerical simulation of earthquake generation cycle along the Japan Trench
In subduction zones, magnitude range of fast interplate earthquakes is generally continuous and followed by the power law in seismically active areas. We have approximated spatial heterogeneity of M~7 and M~9 earthquakes as circular or rectangular patches and treated them as one- or two-hierarchical structure along the Japan Trench (Nakata et al., 2016; 2021; 2023). However, it is important to explain various phenomena in a model by including hierarchical characteristics.
To reproduce as much seismic activity for over a long period as possible in a simple model, we conducted quasi-dynamic numerical simulations of earthquake generation cycles based on the rate- and state-dependent friction law by adopting a multiscale circular patch model (Ide and Aochi, 2013) for off Sanriku region, northern segment of the Japan Trench. The multiscale patch model was used by Ide & Aochi (2013) to document the complex dynamic rupture process of the 2011 Tohoku-Oki earthquake. To determine the spatial heterogeneity of seismic events, historical earthquakes with magnitude more than 5.6 recorded since 1896 within the targeted area were referred. We divided them into four groups according to magnitude. The characteristic slip distance was set to be constant within each group and proportional to the patch radius. We assumed uniform A-B and velocity weakening regardless of the magnitude of the earthquake.
As a result, the magnitude-frequency distribution of simulated earthquakes partly followed the power law with magnitude range of smaller than the characteristic earthquake. Large to moderate earthquakes ruptured simultaneously with closely spaced and partially overlapping patches, showing the complex earthquake cycles with a wide range of magnitudes. It is suggested that historical earthquakes may have occurred repeatedly at the same location, in a combination of multiple patches. In models without the smallest patches in various combinations of four groups of patches, there did not seem to be a significant effect on the characteristics of larger earthquakes except for the rupture initiation. On the other hand, the absence of the largest patch will affect the slip distribution and recurrence intervals for small to moderate earthquakes. Our results suggest that a hierarchical structure is fundamentally important in simulating not only the dynamic rupture process, but also physical processes of long-term earthquake cycles.
To reproduce as much seismic activity for over a long period as possible in a simple model, we conducted quasi-dynamic numerical simulations of earthquake generation cycles based on the rate- and state-dependent friction law by adopting a multiscale circular patch model (Ide and Aochi, 2013) for off Sanriku region, northern segment of the Japan Trench. The multiscale patch model was used by Ide & Aochi (2013) to document the complex dynamic rupture process of the 2011 Tohoku-Oki earthquake. To determine the spatial heterogeneity of seismic events, historical earthquakes with magnitude more than 5.6 recorded since 1896 within the targeted area were referred. We divided them into four groups according to magnitude. The characteristic slip distance was set to be constant within each group and proportional to the patch radius. We assumed uniform A-B and velocity weakening regardless of the magnitude of the earthquake.
As a result, the magnitude-frequency distribution of simulated earthquakes partly followed the power law with magnitude range of smaller than the characteristic earthquake. Large to moderate earthquakes ruptured simultaneously with closely spaced and partially overlapping patches, showing the complex earthquake cycles with a wide range of magnitudes. It is suggested that historical earthquakes may have occurred repeatedly at the same location, in a combination of multiple patches. In models without the smallest patches in various combinations of four groups of patches, there did not seem to be a significant effect on the characteristics of larger earthquakes except for the rupture initiation. On the other hand, the absence of the largest patch will affect the slip distribution and recurrence intervals for small to moderate earthquakes. Our results suggest that a hierarchical structure is fundamentally important in simulating not only the dynamic rupture process, but also physical processes of long-term earthquake cycles.