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Frictional heterogeneities can promote disordered slip evolution on faults

We consider that a slip instability nucleates an earthquake. Past studies found blow-up solutions for diverging slip velocities. Prior stability analyses, considering heterogeneous frictional properties revealed that stable blow-up solutions can predictably dictate earthquake-nucleating instabilities. In this prior analysis, the focus remained mainly on the attraction to stable blow-up solutions. Here, we shift the focus of discussion towards unstable blow-up solutions, in particular, we seek frictional heterogeneities that can make all blowup solutions to lose stability. (We consider variations in direct and evolution effect parameters, a(x) and b(x), and pressume that Dc and σ are uniform). We find that faults that include rate-strengthening regions can lack attractive blow-up solutions. In such scenarios, a rate-weakening fault that includes appropriate ratestrengthening regions can significantly delay the development of an instability compared to a fault that is entirely rate-weakening. That delay can be attributed to the loss of stability of the blow-up solutions. Owed to the non-existence of attractive blow-up solutions, the developing slip velocity fails to converge to a specific distribution at a single location. The near-chaotic transient dynamics may give rise to tremor-like activities.