5:15 PM - 7:15 PM
[SSS10-P02] Investigation of the Physical Mechanism of Adjacent Slow and Repeating Earthquakes Using a Wavy Frictional Heterogeneity Model
Keywords:Frictional heterogeneity, Rate- and state-dependent friction (RSF) law, Spectral boundary integral equation method, Slow earthquakes, Repeating earthquakes, Tremors
Seismological and geological approaches suggest that friction is heterogeneously distributed on the fault plane. As an example, Yabe and Ide (2018) investigated the effects of frictional heterogeneity on seismicity by setting velocity-strengthening and velocity-weakening patches based on the a-b values of the rate- and state-dependent friction (RSF) law. They configured frictional heterogeneity by alternately placing these patches and conducted earthquake cycle simulations. Their results demonstrated that varying the degree of frictional heterogeneity could reproduce diverse seismicity, indicating that regional differences in seismicity may depend on the characteristics of frictional heterogeneity.
This study assumes frictional heterogeneity and attempts to model the phenomenon in which slow earthquakes and (repeating) earthquakes occur in nearly the same location due to the influence of aseismic slip (e.g., Todd et al., 2018; Takahashi et al., 2022). In addition to the conventional bimodal frictional properties, where the a-b value within each patch is constant, we also examine a wavy frictional property, where the a-b distribution is given by a sine function. This wavy frictional property is a model that accounts for the transient variation of frictional properties due to factors such as pore fluid pressure and mineral composition changes. Furthermore, to clarify the impact of aseismic slip occurring in the velocity-strengthening regions between velocity-weakening patches, the individual velocity-weakening patches were set to be smaller than the critical nucleation size (the minimum patch size required for spontaneous seismic fast slip).
Under these conditions, we performed two-dimensional in-plane earthquake cycle simulations, including dynamic terms, following the methodology of Lapusta et al. (2000). When the interaction between velocity-weakening patches was weak, spontaneous events (tentatively referred to as slow earthquakes) frequently occurred, which did not lead to seismic fast slip, as expected from the critical nucleation size setting. However, when the interaction between velocity-weakening patches was strong, particularly in the wavy frictional heterogeneity model, aseismic slip in the velocity-strengthening regions between velocity-weakening patches often led to stress accumulation on the velocity-weakening patches. In such cases, local acceleration occurred on the velocity-weakening patches where slow earthquakes typically occur, leading to the triggering of seismic fast slip.
In our model, the distinction between slow and seismic fast slip events occurring within the same velocity-weakening patch arises from aseismic slip in adjacent velocity-strengthening regions, highlighting the essential role of frictional heterogeneity. This study proposes a physical mechanism that may explain the closely located tremor and (repeating) earthquake occurrences reported in the shallow subduction zones offshore of New Zealand and Northeastern Japan.
This study assumes frictional heterogeneity and attempts to model the phenomenon in which slow earthquakes and (repeating) earthquakes occur in nearly the same location due to the influence of aseismic slip (e.g., Todd et al., 2018; Takahashi et al., 2022). In addition to the conventional bimodal frictional properties, where the a-b value within each patch is constant, we also examine a wavy frictional property, where the a-b distribution is given by a sine function. This wavy frictional property is a model that accounts for the transient variation of frictional properties due to factors such as pore fluid pressure and mineral composition changes. Furthermore, to clarify the impact of aseismic slip occurring in the velocity-strengthening regions between velocity-weakening patches, the individual velocity-weakening patches were set to be smaller than the critical nucleation size (the minimum patch size required for spontaneous seismic fast slip).
Under these conditions, we performed two-dimensional in-plane earthquake cycle simulations, including dynamic terms, following the methodology of Lapusta et al. (2000). When the interaction between velocity-weakening patches was weak, spontaneous events (tentatively referred to as slow earthquakes) frequently occurred, which did not lead to seismic fast slip, as expected from the critical nucleation size setting. However, when the interaction between velocity-weakening patches was strong, particularly in the wavy frictional heterogeneity model, aseismic slip in the velocity-strengthening regions between velocity-weakening patches often led to stress accumulation on the velocity-weakening patches. In such cases, local acceleration occurred on the velocity-weakening patches where slow earthquakes typically occur, leading to the triggering of seismic fast slip.
In our model, the distinction between slow and seismic fast slip events occurring within the same velocity-weakening patch arises from aseismic slip in adjacent velocity-strengthening regions, highlighting the essential role of frictional heterogeneity. This study proposes a physical mechanism that may explain the closely located tremor and (repeating) earthquake occurrences reported in the shallow subduction zones offshore of New Zealand and Northeastern Japan.