ИСТИНА

Comparative analysis was conducted for the dynamics of reservoir induced seismicity (RIS) in the seismic area of Koyna-Warna (Western India) and for annual variations of the water level in reservoirs during the period of 1968-2012. The cyclic variations of water levels cause a cyclic response of seismicity in the seismic area between the Koyna and Warna reservoirs. The spring peak of RIS corresponds to the beginning of annual reservoir unloading after six months of approximately constant high levels. This maximum is present at not all times and increases after Warna reservoir filling. It can be assumed that the maximum is of kinetic origin, linked with fluid pressure diffusion, long-term rock strength and stress-corrosion. The autumn peak corresponds to the final stage of reservoir loading and rising of maximum water level. It can be assumed that it is of dynamic origin, induced by direct impact of additional water pressure and the rate of its variations. An additional winter peak appears during loading of the Warna reservoir and coincides with the interval of maximal water level. Temporal changes of amplitudes of annual peaks of seismicity found to be not correlated with the water level variations. It is assumed that triggered seismicity in this region is caused by a combination of dynamic and kinetic factors, i.e. accumulation of stresses and water diffusion into the massive. Modern laboratory equipment and technique allow to model natural triggered seismicity by the initiation of acoustic activity in the loaded sample. The penetration of water from the surface of the sample into the inner part initiates acoustic emission swarms, which migrate to the area of increased stress and results in forming a macrocrack. The revealed features of temporal variations of parameters of the acoustic regime at the stages of excitation and decay of acoustic activity are qualitatively similar to those in the seismic regime. Changes of stress field after stick-slips result in the destruction of the acoustic response to the periodical axial loading modulation. The study was carried out under a project supported by the RSF, grant 16-47-02003.