The gradual transition from stick-slip to stable sliding is studied in lab experiments. The results allow concluding, that the sliding mode and the part of deformation energy spent to the seismic radiation are determined by a ratio of two parameters—the fault stiffness and the stiffness of surrounding rock massif. This conclusion gives new explanation for huge scatter of the values of radiated energy of earthquakes with close seismic moments. Presence of some minerals and water in the fault principal slip zone can essentially reduce the shear stiffness of a fault and the radiation efficiency of a fault slip.
The 2008 workshop on a Long Range Science Plan for Seismology (Lay 2009) considered promising research directions for the next decades and identified 10 Seismological Grand Challenge research questions. The First Grand Challenge was formulated as "How the faults slip?" In the frames of this problem several key questions and issues were formulated. Among these questions was the following: "What physical properties control diverse types of fault sliding?" and "What governs transitions from stick-slip behavior to steady sliding?"