| Abstrakt: |
A variety of mechanisms have been proposed to explain how a fault might deform relatively slowly, rather than manifesting as earthquakes. Several rely on the frictional properties of the fault interface. In this study I analyze the slip stability of a fluid‐infiltrated fault in the framework of a microphysically‐based friction model, which has shear zone porosity as its state variable. Linear stability analysis of the model, incorporating the evolution of fluid pressure, gives the critical stiffness (kc ${k}_{c}$) and frequency (wc ${w}_{c}$) as a function of normalized dilatancy (E/Ec $E/{E}_{c}$) and diffusivity (U $U$) factors. The theoretical results are similar to those derived from the previous friction laws, except that a positive kc ${k}_{c}$ always exists, even for a highly‐dilatant, impermeable fault where the value is proportional to the diffusivity. This implies that dilatant faults in impermeable media are potentially seismogenic, while the previous models predict negative kc ${k}_{c}$, implying a stable fault regardless of loading stiffness (k). Adopting a spring‐slider fault analogue, the analytical results are verified numerically under a wide span of spring stiffness, dilatancy, and diffusivity factors. The numerical results further reveal that four different modes of periodic slow slips can emerge in the model, without invoking inertia, which is distinct from previous friction models. Translating kc ${k}_{c}$ into the scenario of an elastically‐deformable medium, the critical wavelength on a dilatant fault can be as long as tens of kilometers. Gaining insights from all these features, I posit that the microphysical model is inherently favorable for generating slow slips. Plain Language Summary: As stress accumulates, a frictional interface can move either suddenly or slowly. The same phenomenon also occurs in natural fault zones. Until very recently, the slow motion of the fault interface (so‐called "slow slips") was observed in the subduction zones such as those in Japan. For the purpose of modeling these slow fault motion processes, a useful result would be a physically‐based constitutive relation that well characterizes the relevant observations and underlying mechanisms. This study analyzes the motion behavior of a fluid‐infiltrated fault zone in the framework of a microphysically‐based friction model, that is, slow and continuous sliding versus episodic acceleration of slip, like earthquakes. Interestingly, four mechanisms that have been previously proposed and widely used in the simulations to damp an accelerated fault emerge naturally from the analyzed model. The theoretical analysis further tells that the microphysical model is inherently favorable for the generation of slow fault slips. Key Points: Various damping regimes emerge as slip accelerates in a fluid‐infiltrated faultEven highly dilatant and low‐permeability faults are potentially unstableFour distinct types of slow slip events are predicted by the microphysical friction model [ABSTRACT FROM AUTHOR] |
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