STRONG INDUCED EARTHQUAKES IN MINING AREAS

Strong induced earthquakes remain one of the most sensitive information issues for society, causing people’s concern. In addition, the study of induced earthquakes provides chances to identify cause-and- effect relationships in the process of preparation and origin of the seismic event, to establish parameters that can be used to control the ongoing processes. The article summarizes the results of recent years working on the occurrence of strong induced earthquakes in the mining areas in the conditions for initiating dynamic slip-type events (type II) are described. Changes in Coulomb stresses on the fault plane are analyzed, as well as various factors that can cause such changes. It is shown that if the Coulomb stress changes reach several tenths of MPa on the fault plane of a significant size, significantly exceeding the area of the earthquake nucleation zone, then even a small value of one percent of the natural stress level may be sufficient to initiate seismogenerating movements along the stressed fault. Calculations performed for large quarries occupying about 20 km2 (like the Bachatsky quarry in Kuzbass) have demonstrated that the extraction and movement of rock masses in such an area can bring closer the moment of occurrence of an earthquake with a magnitude of M ~ 6, already prepared by the natural evolution of the mountain massif. At the same time, the formation of large rock dumps during the development of such large quarries does not contribute to the initiation of large seismic events. An extensive network of underground workings in the vicinity of a tectonic fault has a noticeable effect on the effective rigidity of the massif and on the possibility of fault slip. However, the practice of laying chambers with destroyed rock significantly reduces the likelihood of such a negative scenario. The issue of discrimination of natural and man-made events is also considered, since it is important not only for public opinion, but also for the separation of the area of responsibility of state structures and insurance companies, on the one hand, and companies exploiting the subsoil, on the other. The identified types and parameters of anthropogenic impacts will help to reasonably determine restrictions on certain types of work, which, in turn, will reduce the likelihood of catastrophic earthquakes in mining areas. In addition, the potential of induced earthquakes should be taken into account when assessing seismic hazards, especially in areas where responsible energy and engineering facilities are located.