By comparing laboratory earthquakes with numerically simulated ruptures, we find that certain properties inside the rupture front may not always be accessible to direct measurements in the real world, due to a lack of resolution caused by the shrinking size of rupture front zone (Lorentz contraction). Although a variety of friction laws have been proposed based on measurements made in the lab, uncertainty remains regarding to what extent those measurements capture the true rupture properties. When ruptures propagate in the direction of applied shear in the softer material, we demonstrate that cT provides an explanation for how and when slip pulses (new rupture modes characterized by spatially localized slip) are generated.Įarthquake rupture propagation along a fault interface depends on the governing friction law. When the rupture direction opposes the direction of applied shear in the softer material, we show that cT is the subsonic limiting velocity. As rupture velocities increase, we experimentally and theoretically show how bimaterial cracks become unstable at a subsonic critical rupture velocity, cT. At low rupture velocities, bimaterial coupling is not very significant and interface rupture is governed by ‘bimaterial cracks’ that are described well by LEFM. When the elastic properties of the two materials are dissimilar, many new effects take place that result from bimaterial coupling: the normal stress at the interface is elastodynamically coupled to local slip rates. When the materials are similar, recent experimental and theoretical work has shown that shear cracks described by Linear Elastic Fracture Mechanics (LEFM) quantitatively describe the rupture of frictional interfaces. Interface rupture dynamics depend markedly on the mechanical properties of the bulk materials that bound the frictional interface. The rupture of the interface joining two materials under frictional contact controls their macroscopic sliding. This coupling between friction and fracture is critical to our fundamental understanding of frictional motion and related processes, such as earthquake dynamics. In addition, the energy dissipated in the fracture of the contacts remains nearly constant throughout the entire range in which the rupture velocity is less than the Rayleigh wave speed, whereas the size of the dissipative zone undergoes a Lorentz-like contraction as the rupture velocity approaches the Rayleigh wave speed. We find that these singular solutions, originally derived to describe brittle fracture, are in excellent agreement with the experiments for slow propagation, whereas some significant discrepancies arise as the rupture velocity approaches the Rayleigh wave speed. Here we show that the transition from 'static' to 'dynamic' friction is quantitatively described by classical singular solutions for the motion of a rapid shear crack. We investigated the onset of dry frictional motion by performing simultaneous high-speed measurements of the real contact area and the strain fields in the region surrounding propagating rupture tips within the dry (nominally flat) rough interfaces formed by brittle polymer blocks. These range from modelling friction with a single degree of freedom, a 'friction coefficient', to theoretical treatments using dynamic fracture to account for spatial and temporal dynamics along the interface. There are a variety of views on how best to describe the onset of dry frictional motion. Frictional processes entail the rupture of the ensemble of discrete contacts defining a frictional interface.
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