Abstract
Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. However, the origin of this variation of the rupture velocity in nature as well as the physics behind it is still debated. Here, we first highlight how the different types of fault slip observed in nature appear to stem from the same physical mechanism. Second, we reproduce at the scale of the laboratory the complete spectrum of rupture velocities observed in nature. Our results show that the rupture velocity can range from a few millimetres to kilometres per second, depending on the available energy at the onset of slip, in agreement with theoretical predictions. This combined set of observations bring a new explanation of the dominance of slow rupture fronts in the shallow part of the crust or in areas suspected to present large fluid pressure.
Highlights
Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures
Making the hypothesis that slow slip events consist of rupture propagating circularly at a constant rupture velocity, i.e., as most regular earthquakes, we can normalise the seismic moment of each event by their average stress drops and multiply their durations (δ) by their average rupture velocities (Vr)
For each confining pressure tested, the rupture velocity seems to increase with the decrease in the ratio between the average fluid pressure and the average normal stress (λ = Pf/σn) acting on the fault at the onset of propagation (Figs. 5 and 6a)
Summary
Modern geophysics highlights that the slip behaviour response of faults is variable in space and time and can result in slow or fast ruptures. This normalised scaling reveals that the different moment-duration relations could just be related to variations in both stress drop and rupture speed (Fig. 1b), in agreement with recent studies[10] This could imply three important consequences: (i) the stress drop during events is a function of the rupture velocity; (ii) since most SSEs present pulse-like behaviour, the rupture velocity increases during rupture propagation[12]; and (iii) both slow and fast earthquakes are governed by similar physics. The promotion of slow slip events rather than regular earthquakes in areas presenting high fluid pressure was generally explained by an increase in the nucleation length with increasing fluid pressure, as expected by both rate-and-state and slipweakening theories[25,29,30,31,32] Such behaviour has been observed experimentally by the reproduction of a quasi-static rupture mode, such as stable slip[33,34,35,36]. Our results show that when the nucleation length is within the fault length, a b
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