Seismic-Acoustics of a Block Sliding Along a Fault

Frictional instability is the most likely mechanism of shallow earthquakes. For better understanding fault behavior we have conducted field experiments on shear deformation of a model fault. This study has focused on revealing the seismic-acoustic signatures of fault behavior. The entire spectrum of sliding regimes has been realized in the course of 1-m scale experiments—from a stable creep to a regular stick–slip, and their seismic-acoustic characteristics were investigated. It is shown that seismic pulses with characteristic frequencies less than 500 Hz are emitted only during slip events. The acoustic emission (AE) is observed both during slip events and at the stage of their preparation. Statistical analysis has shown that the AE distribution is generally a superposition of a power law distribution for low-energy pulses and a peak-like distribution for the largest pulses. The distribution with a characteristic peak prevails in regular stick–slip, while (quasi)stable creep is characterized by the power law distribution over the entire range of amplitudes. Both distributions—“with peak” and “without peak”—are observed for irregular sliding regime (random slip events with various amplitudes). Applying the nonlinear Grassberger-Procaccia algorithm to the analysis of time-series of AE data has allowed to rank the fault sliding regimes. The calculated correlation dimension characterizes the dynamics of the fault. The highest dimension is typical for stable sliding. A decrease of the correlation dimension indicates an enhanced probability of high-amplitude slip events. Nucleation of largest slip events is observed for the regular stick–slip with the least correlation dimension.