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[SCG40-P42] An attempt to express various types of slip using a simple friction law
Keywords:friction law, seismic slip, slow slip
We are trying to model various types of fault slip using as few variables and parameters as possible in order to understand the current situation and forecast the transition of locking and sliding at plate boundaries. Specifically, the friction law does not consider direct effects, and the strength evolution law only considers slip weakening and strength recovery. We investigated the response of a one-degree-of-freedom spring block system, which does not take into account inertial effects and includes radiation damping, when subjected to spontaneous slip and changes in external force. In conclusion, the diversity of spontaneous slips is reproduced to some extent by differences in slip weakening rates, but the duration of SSE and the response duration to external forces are only short due to the effect of radiation damping. It can be said that effects such as direct effect or viscoelasticity are necessary to obtain longer duration that is close to the actual phenomenon.
Diversity of spontaneous slips: When the slip weakening distance is increased, the maximum slip velocity, stress drop amount, slip amount, and recurrence interval in repeated spontaneous stick-slip events decrease by an order of magnitude after reaching a critical value. These are similar to SSE. On the other hand, although the duration increases by an order of magnitude, it is an order of magnitude shorter than that of SSE with the same recurrence interval.
Response when external force (10% of strength) is applied: When external force is applied during steady slip, it accelerates all at once to Vmax, then gradually decelerates and returns to steady slip at Vo. As Vmax decreases according to Dc, the duration until returning to steady slip becomes longer, but it reaches a plateau. Also, if it applied during SSE or when it is locked, it will accelerate and decelerate to Vmax and become locked, and once the stress increases and strength is reached again, then SSE will be repeated again. The duration during both acceleration and deceleration is shorter than during SSE.
As a future issue, in order for the duration to be close to reality, the damping needs to be larger, and it is necessary to introduce direct effects or viscoelasticity. In addition, when responding to external forces, when decelerating after accelerating, there are cases where the speed does not decelerate below the loading speed and becomes a steady slip. And three are other cases where it decelerates further and becomes locked, and then a spontaneous slip will occur later. In the future, we will verify whether the behavior corresponding to these is observed in real afterslip, and particularly investigate the latter case, in order to understand the mechanism by which the transition to the occurrence of earthquakes and SSEs occurs after afterslip
Diversity of spontaneous slips: When the slip weakening distance is increased, the maximum slip velocity, stress drop amount, slip amount, and recurrence interval in repeated spontaneous stick-slip events decrease by an order of magnitude after reaching a critical value. These are similar to SSE. On the other hand, although the duration increases by an order of magnitude, it is an order of magnitude shorter than that of SSE with the same recurrence interval.
Response when external force (10% of strength) is applied: When external force is applied during steady slip, it accelerates all at once to Vmax, then gradually decelerates and returns to steady slip at Vo. As Vmax decreases according to Dc, the duration until returning to steady slip becomes longer, but it reaches a plateau. Also, if it applied during SSE or when it is locked, it will accelerate and decelerate to Vmax and become locked, and once the stress increases and strength is reached again, then SSE will be repeated again. The duration during both acceleration and deceleration is shorter than during SSE.
As a future issue, in order for the duration to be close to reality, the damping needs to be larger, and it is necessary to introduce direct effects or viscoelasticity. In addition, when responding to external forces, when decelerating after accelerating, there are cases where the speed does not decelerate below the loading speed and becomes a steady slip. And three are other cases where it decelerates further and becomes locked, and then a spontaneous slip will occur later. In the future, we will verify whether the behavior corresponding to these is observed in real afterslip, and particularly investigate the latter case, in order to understand the mechanism by which the transition to the occurrence of earthquakes and SSEs occurs after afterslip