Evolution of Sliding Along a Heterogeneous Fault. A Large-Scale Laboratory Experiment

—A laboratory setup was constructed in IDG RAS to investigate the process of shearing the contact of rock blocks of one-meter scale. It was used to investigate deformation processes in a fault with a heterogeneous structure of the sliding interface, which contained strong contact patches—analogs of the asperity in the well-known model of Hiroo Kanamori (Kanamori and Stewart, 1978). It is shown that when a large slip occurs, the rupture, which starts in the zone of maximal deficit of interblock displacement, cuts the segments of the fault with lower effective strength, the latter being decreased in previous deformation events. Those previous events may be “slow” slips with low seismic efficiency. In nature the events that “prepare” the fault interface for a large slip may be smaller earthquakes—foreshocks, or they can be either low frequency earthquakes or slow slip events, both can hardly be detected in seismic records. Thereupon a promising diagnostic indication is the shift of the spectrum of ambient seismic noise to lower frequencies caused by the decrease of fault stiffness.