16:45 〜 17:00
[S08-07] Multi-Scale Rate- and Roughness-Dependent Friction Realizes a Variety of Seismic-Aseismic Transitions
We applied a rate- and state-dependent friction law, which accounted for multi-scale roughness evolution, to a spring-slider model and found a variety of seismic-aseismic transitions for a single set of frictional parameters. By adding the direct effect, we modernized the previously proposed law for frictional strength (Aochi & Matsu’ura, 2002). This law considers the statistically self-Affine fault topography as a "state", and each Fourier amplitude of the corresponding angular wave number evolves as a function of the slip rate (V) and itself.The modernized law realizes the rate-weakening property only in a restricted range of V. The evolution of the state for a small wavenumber requires a much longer slip than that for a single stick-slip event, resulting in a gradual change in event characteristics. As the property of the limit cycles, the maximum V changes gradually from aseismic to seismic values as a function of spring stiffness. This is not the case for standard rate-and-state friction laws with a single state variable. It also showed loading-rate dependence of bifurcation behavior at the stability transition. Faster loading produces a supercritical Hopf bifurcation, and a single stable limit cycle attracts the trajectories starting from everywhere in the phase space, as long as being simulated. On the other hand, slower loading produces a subcritical Hopf bifurcation, and a conditionally stable fixed point coexists with a large-amplitude stable limit cycle. The conditional stability leads to a timing-dependent response to perturbations of the loading rate. Specifically, for the same negative velocity steps, the fault behavior changes to either seismic or aseismic depending on the timing of the perturbation. Our result indicates potential complexity in the change in a fault's seismic/aseismic property on a perturbation of loading condition, which has significant implications for the real seismic cycles. As an ongoing study, we applied the modernized law to a continuum model and simulated a sequence of earthquakes with an adaptive time stepper (Romanet & Ozawa, 2022) to investigate the scaling of the source parameters.