5:15 PM - 6:30 PM
[SCG39-P09] Modeling slow earthquakes by competing time scale of rupture propagation, stress loading and strength healing
Keywords:Cellular automata models, Tremor, Low-frequency earthquakes, Slow Slip Event
Slow earthquakes, which have been actively studied in recent years, are phenomena with a wide range of propagation velocities on the order of 0.1 m/s (SSE) to 10 m/s (LFE) and a duration of several years (SSE) to 0.1 s (LFE) with a wide range of time constants [Ide et al., 2007]. The purpose of this study is to investigate the possibility of using cellular automaton models to comprehensively model the behavior of a wide range of slow earthquakes using the widely varying propagation time constant as a parameter.
Conventional studies of cellular automata models have aimed at modeling regular earthquakes, and have assumed that the time constant of stress accumulation is negligible compared to the time constant of rupture propagation [Carlson and Langer,1989:Olami et al.,1992]. However, in slow earthquakes with slow rupture propagation, these two time constants may be in competition. In order to discuss how this effect affects the statistical properties, the Dynamic OFC model is an extension of the Olami_Feder_Christensen model that reproduces the GR law well. This model is incorporating a finite rupture chain time constant and a loading time constant. In the Dynamic OFC model, the competition between these two time constants is known to produce continuous events, and this behavior reproduces the point that the tremor is swarms of low-frequency earthquakes.
The Dynamic OFC model discussed so far incorporates the assumption that the rupture threshold (corresponding to the strength) does not change even at the end of one rupture step, which implies that the strength recovery is very fast in relation to the rupture chain (i.e., the rupture chain is slow). In this study, the model was extended to include a new parameter, the ratio of the time constant of loading and strength recovery to the time constant of the fracture chain. This model is capable of discussing slow phenomena (slow fracture propagation) and fast phenomena (fast fracture propagation) in a unified manner, using the competition between the two time constants of (1) fracture and stress accumulation, and (2) fracture and strength recovery as parameters.
In the parameter range of the slow phenomenon (slow fracture propagation) of the present model, a transition from continuous behavior such as the tremor to periodic behavior such as that seen in SSE was observed depending on the combination of the two parameters. We will also discuss whether such a model can comprehensively explain the characteristics of slow earthquakes with various time constants. The results of this model in the parameter range of fast phenomena (fast rupture propagation) will be presented in the S-SS06 session.
Conventional studies of cellular automata models have aimed at modeling regular earthquakes, and have assumed that the time constant of stress accumulation is negligible compared to the time constant of rupture propagation [Carlson and Langer,1989:Olami et al.,1992]. However, in slow earthquakes with slow rupture propagation, these two time constants may be in competition. In order to discuss how this effect affects the statistical properties, the Dynamic OFC model is an extension of the Olami_Feder_Christensen model that reproduces the GR law well. This model is incorporating a finite rupture chain time constant and a loading time constant. In the Dynamic OFC model, the competition between these two time constants is known to produce continuous events, and this behavior reproduces the point that the tremor is swarms of low-frequency earthquakes.
The Dynamic OFC model discussed so far incorporates the assumption that the rupture threshold (corresponding to the strength) does not change even at the end of one rupture step, which implies that the strength recovery is very fast in relation to the rupture chain (i.e., the rupture chain is slow). In this study, the model was extended to include a new parameter, the ratio of the time constant of loading and strength recovery to the time constant of the fracture chain. This model is capable of discussing slow phenomena (slow fracture propagation) and fast phenomena (fast fracture propagation) in a unified manner, using the competition between the two time constants of (1) fracture and stress accumulation, and (2) fracture and strength recovery as parameters.
In the parameter range of the slow phenomenon (slow fracture propagation) of the present model, a transition from continuous behavior such as the tremor to periodic behavior such as that seen in SSE was observed depending on the combination of the two parameters. We will also discuss whether such a model can comprehensively explain the characteristics of slow earthquakes with various time constants. The results of this model in the parameter range of fast phenomena (fast rupture propagation) will be presented in the S-SS06 session.