The Emergence of Four Types of Slow Slip Cycles on Dilatant, Fluid Saturated Faults

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 (k(c)) and frequency (w(c)) as a function of normalized dilatancy (E/E-c) and diffusivity (U) factors. The theoretical results are similar to those derived from the previous friction laws, except that a positive 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 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 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.

Automated summary

In this study, the slip stability of a fluid-infiltrated fault is analyzed using a microphysical friction model. The results show the possibility of four different modes of slow slips without invoking inertia, suggesting that the microphysical model is favorable for generating slow slips.