ИСТИНА

The results of the laboratory experiment on the initiation of acoustic emission in a loaded specimen by wetting a part of its surface without a considerable increase in the pore pressure are analyzed. The experiment was conducted on the lever press in the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. Infusion of water into the surface of the specimen initiated the swarm acoustic emission, which, after having migrated to the area with higher stresses, culminated in the formation of a macrofracture. The analysis revealed the regularities in the excitation and relaxation of the acoustic activity in response to the different types of the initiation: - the “forced” excitation by stepwise increasing the load at the initial stage of the experiment; - excitation resulting from fluid diffusion, which can be associated with the reduction in the material strength due to wetting; - excitation that reflects the preparation for the emergence of a macrofracture in the area with the highest Coulomb stresses; - spontaneous excitation of swarm activity at the stage of relaxation of the acoustic emission after the formation of macrofracture. The features revealed in the acoustic time series at the stages of excitation and decay of the emission are qualitatively similar to the trends identified in the variations of seismic parameters during the natural swarms, preparation of the sources of the strong earthquakes, and relaxation of the aftershocks. In particular, the obtained results support the hypothesis of fluid initiation of non-volcanic seismic swarms.