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.
The failure of frictional interfaces -the process of frictional rupture -is widely assumed to feature crack-like properties, with far-reaching implications for various disciplines, ranging from engineering tribology to earthquake physics. A necessary condition for the emergence of a crack-like behavior is the existence of stress drops in frictional rupture, whose basic physical origin has been recently elucidated. Here we show that for generic and realistic frictional constitutive relations, and once the necessary conditions for the emergence of an effective crack-like behavior are met, frictional rupture dynamics are approximately described by a crack-like, fracture mechanics energy balance equation. This is achieved by independently calculating the intensity of the crack-like singularity along with its associated elastic energy flux into the rupture edge region, and the frictional dissipation in the edge region. We further show that while the fracture mechanics energy balance equation provides an approximate, yet quantitative, description of frictional rupture dynamics, interesting deviations from the ordinary crack-like framework -associated with non-edge-localized dissipation -exist. Together with the recent results about the emergence of stress drops in frictional rupture, this work offers a comprehensive and basic understanding of why, how and to what extent frictional rupture might be viewed as an ordinary fracture process. Various implications are discussed.
The onset of rapid slip along initially quiescent frictional interfaces, the process of "earthquake nucleation", and dissipative spatiotemporal slippage dynamics play important roles in a broad range of physical systems. Here we first show that interfaces described by generic friction laws feature stress-dependent steady-state slip pulse solutions, which are unstable in the quasi-1D approximation of thin elastic bodies. We propose that such unstable slip pulses of linear size L * and characteristic amplitude are "critical nuclei" for rapid slip in a non-equilibrium analogy to equilibrium first-order phase transitions, and quantitatively support this idea by dynamical calculations. We then perform 2D numerical calculations that indicate that the nucleation length L * exists also in 2D, and that the existence of a fracture mechanics Griffith-like length LG < L * gives rise to a richer phase-diagram that features also sustained slip pulses. arXiv:1807.06890v2 [physics.geo-ph]
The failure of frictional interfaces -the process of frictional rupture -is widely assumed to feature crack-like properties, with far-reaching implications for various disciplines, ranging from engineering tribology to earthquake physics. Yet, how the effective crack-like behavior emerges from basic physics and what its range of validity is are not understood. Here we show that for rapid rupture a finite and well-defined stress drop, which is a necessary condition for the existence of a crack-like behavior, is directly related to wave radiation from the frictional interface to the bulks surrounding it (the so-called radiation damping effect) and to long-range bulk elastodynamics, and not exclusively to interfacial physics. Furthermore, we show that the emergence of a stress drop is a finite time effect, mainly limited by the wave travel time in finite systems. The results for rapid rupture are supplemented by predictions for slow rupture. All of the theoretical predictions are supported by available experimental data and by extensive computations. They offer a comprehensive and basic understanding of why, how and to what extent frictional rupture might be viewed as an ordinary fracture process. I. BACKGROUND AND MOTIVATIONRapid slip along interfaces separating bodies in frictional contact is mediated by the spatiotemporal dynamics of frictional rupture [1,2]. Frictional rupture is a fundamental process of prime importance for a broad range of physical systems, e.g. it is responsible for squealing in car brake pads [3], for bowing on a violin string [4], and for earthquakes along geological faults [5][6][7], to name just a few well-known examples. The essence of frictional rupture propagation is that a state of relatively high slip rate (the rate of interfacial shear displacement discontinuity) behind the rupture edge propagates into a low/vanishing slip rate state ahead of it, cf. Fig. 1. As such, frictional rupture appears to be essentially similar to ordinary tensile (opening) cracks, where a finite tensile displacement discontinuity (broken material) state behind the crack edge propagates into a zero tensile displacement discontinuity (intact material) state ahead of it [8].There is, however, an important fundamental difference between frictional rupture and ordinary tensile cracks that manifests itself in the stress states associated with these two processes. A tensile crack is composed of surfaces that cannot support stress, so the stress behind its edge vanishes. Consequently, tensile crack propagation is a process in which far-field driving stresses that characterize the material state far ahead of the crack edge are eliminated altogether behind it. The stress drop that accompanies tensile crack propagation has dramatic implications. Most notably, the loss of stress bearing capac- * eran.bouchbinder@weizmann.ac.il † jean-francois.molinari@epfl.ch ity along the crack surfaces is compensated by large concentration of deformation and stress near the crack edge, oftentimes in a way that mimics a mathematical s...
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