The multi-scale roughness of a fault interface is responsible for multiple asperities that establish a complex and discrete set of real contacts. Since asperities control the initiation and evolution of the fault slip, it is important to explore the intrinsic relationships between the collective behavior of local asperities and the frictional stability of the global fault. Here we propose a novel analog experimental approach, which allows us to capture the temporal evolution of the slip of each asperity on a faulting interface. We find that many destabilizing events at the local asperity scale occurred in the frictional strengthening stage which is conventionally considered as the stable regime of a fault. We compute the interseismic coupling to evaluate the slipping behaviors of asperities during the fault-strengthening stage. We evidence that the interseismic coupling can be affected by the elastic interactions between asperities through the embedding soft matrix. Scaling laws of natural slow slip events are reproduced by our setup in particular the moment-duration scaling. We also evidence an unexpected persistency of a disordering of the asperities through the seismic cycles despite the relaxation effects of the large slip events.

Some observations of repeating earthquakes show an unusual, non self-similar scaling between seismic moment and corner frequency, a source property related to rupture size. These observations have been mostly reported in regions at the transition from stable to unstable slip, in geothermal reservoirs and subduction zones. What controls the non self-similarity of these ruptures and how this is linked to the frictional stability of the interface are still open questions. Here we develop seismic cycle simulations of a single unstable slipping patch to investigate the mechanics underlying this behavior. We show that temporal changes of normal stress on a fault can produce ruptures that exhibit the observed anomalous scaling. Our results highlight the role of fault zone fluid pressure in modulating the effective normal stress and contributing to the sliding stability of the fault.

It has long been observed that periods of intense seismic activity in a region alternate with periods of relative quiescence, but establishing whether this is the expected result of purely random fluctuations or is due to some broad-scale physical processes occurring in the Earth is a challenge. We present here compelling observations which show that periods of high seismicity rate and periods of quiescence are synchronized throughout the Anatolian plate. These observations are based on the remarkably similar evolution of the numerous seismic clusters between 2003 and 2017 in Anatolia. Two outside clocks set the timing of these activities, the 2004 M9.2 Sumatra earthquake and the 2008-2011 episode of slab rollback/deformation in the Hellenic subduction. The observed high seismicity rate in the plate which began with the Sumatra earthquake and lasted for about 7 years has been replaced by a relatively uniform quiescence period.