5:15 PM - 6:45 PM
[SCG40-P44] Spontaneous segmentation of slow slip events on a planar uniform fault -Implication from numerical simulations-
Keywords:segmentation of Slow Slip Events (SSEs), Nankai trough, numerical simulation, rate- and state-dependent friction law
Slow slip events (SSEs) often occur adjacent to megathrust seismogenic zones. Understanding the behavior of SSEs is crucial for predicting the occurrence of megaquakes, because the SSE activities may reflect the stress state of the seismogenic zone.
Along the Nankai Trough in southwest Japan, SSEs occur in the deeper extension of the seismogenic zone. The SSEs occur in the divided segments along the strike direction with different recurrence intervals and slip amounts (e.g., Michel et al. 2019a; Takagi et al., 2019). Some SSEs occur independently within segments, while others interact with other segments. For instance, Takagi et al. (2019) showed that SSEs migrate from the southwest to the northeast; from the segment of Hyuga-nada to western Shikoku in the western Nankai region.
The segmentation of SSEs has been attributed to heterogeneity along the strike, including frictional property, effective normal stress, and fault geometry in simulation studies based on laboratory-derived rate and state friction laws (Liu, 2014; Li et al., 2018). However, a plane fault with a uniform property can also produce spontaneous segmentation of SSEs. Ohata (2023) conducted numerical experiments assuming uniform SSE faults and suggested that segmentation arises from the stress heterogeneity, self-organized as the slip evolves on the fault. He showed that critical nucleation size h* (Ruina, 1983; Rice, 1993) determines the SSE size, resulting in the number of SSE segments on a fault inversely proportional to h*.
In this study, following Ohata (2023), we conduct additional experiments to derive the nature of the segmented SSEs in more detail. We employ a long planar fault in the strike direction that subducts at 6 cm/yr. We set uniform rate-weakening frictional properties on the fault, and systematically vary the frictional parameters. As a result, while the number of segments generally increases inversely proportional to h* as shown by Ohata (2023), it also depends on the ratio of friction parameters, a/b and effective normal stress, σ. The SSE size and the number of segments are not only influenced by the frictional properties but also by the initial values of variables, slip rates and state variables. Specifically, symmetric and asymmetric initial conditions result in different numbers of SSE segments. Furthermore, we found that the observable quantities such as the length, location, and recurrence interval of SSEs and the direction of the SSE migration in the uniform fault model can change in response to external conditions such as the stress state.
The simple model used in this study cannot reproduce the differences in recurrence intervals and slip amounts in each SSE segment. However, this study may suggest fundamental properties of SSE segmentation that do not depend on the along-strike heterogeneity.
Along the Nankai Trough in southwest Japan, SSEs occur in the deeper extension of the seismogenic zone. The SSEs occur in the divided segments along the strike direction with different recurrence intervals and slip amounts (e.g., Michel et al. 2019a; Takagi et al., 2019). Some SSEs occur independently within segments, while others interact with other segments. For instance, Takagi et al. (2019) showed that SSEs migrate from the southwest to the northeast; from the segment of Hyuga-nada to western Shikoku in the western Nankai region.
The segmentation of SSEs has been attributed to heterogeneity along the strike, including frictional property, effective normal stress, and fault geometry in simulation studies based on laboratory-derived rate and state friction laws (Liu, 2014; Li et al., 2018). However, a plane fault with a uniform property can also produce spontaneous segmentation of SSEs. Ohata (2023) conducted numerical experiments assuming uniform SSE faults and suggested that segmentation arises from the stress heterogeneity, self-organized as the slip evolves on the fault. He showed that critical nucleation size h* (Ruina, 1983; Rice, 1993) determines the SSE size, resulting in the number of SSE segments on a fault inversely proportional to h*.
In this study, following Ohata (2023), we conduct additional experiments to derive the nature of the segmented SSEs in more detail. We employ a long planar fault in the strike direction that subducts at 6 cm/yr. We set uniform rate-weakening frictional properties on the fault, and systematically vary the frictional parameters. As a result, while the number of segments generally increases inversely proportional to h* as shown by Ohata (2023), it also depends on the ratio of friction parameters, a/b and effective normal stress, σ. The SSE size and the number of segments are not only influenced by the frictional properties but also by the initial values of variables, slip rates and state variables. Specifically, symmetric and asymmetric initial conditions result in different numbers of SSE segments. Furthermore, we found that the observable quantities such as the length, location, and recurrence interval of SSEs and the direction of the SSE migration in the uniform fault model can change in response to external conditions such as the stress state.
The simple model used in this study cannot reproduce the differences in recurrence intervals and slip amounts in each SSE segment. However, this study may suggest fundamental properties of SSE segmentation that do not depend on the along-strike heterogeneity.