Geological, geophysical and seismogeological studies are now conducted in a more detail and thus provide for de termining seismic sources with higher accuracy, from the first meters to first dozens of meters [Waldhauser, Schaff, 2008]. It is now possible to consider uncertainty ellipses of earthquake hypocenters, that are recorded in the updated Earthquake Cata logue, as surfaces of earthquake focus generators. In our article, it is accepted that a maximum horizontal size of an uncer tainty ellipse corresponds to an area of a focus generator, and seismic events are thus classified into two groups, earthquakes with nonstiff and stiff foci. Criteria of such a classification are two limits of elastic strain and brittle strain in case of uniaxial (3⋅10 -5 ) or omnidirectional (10 -6 ) compression. The criteria are established from results of analyses of parameters of seismic dislocations and earthquake foci with regard to studies of surface parameters and deformation parameters of fault zones. It is recommendable that the uniaxial compression criterion shall be applied to zones of interaction between tectonic plates, and the unilateral compression criterion shall be applied to low active (interplate) areas. Sample cases demonstrate the use of data sets on nonstiff and stiff foci for separate evaluation of magnitude reoccurrence curves, analyses of structured and dis sipated seismicity, review of the physical nature of nonlinearity of recurrence curves and conditions of preparation of strong earthquakes. Changes of parameters of the recurrence curves with changes of data collection square areas are considered. Reviewed are changes of parameters of the recurrence curves during preparation for the Japan major earthquake of 11 March 2011 prior to and after the major shock. It is emphasized that it is important to conduct even more detailed geological and geophysical studies and to improve precision and sensitivity of local seismological monitoring networks in zones of nuclear stations and other hazardous facilities. It is noted that a list of parameters recorded in earthquake catalogues needs to be ex tended. Based on the above, it will be possible to ensure proper monitoring of stability of the seismic process during con struction, operations and decommissioning of nuclear stations.

The article presents the basic principles and an algorithm allowing to arrange a seismological monitoring system for the Yeniseiskiy site selected for deep geological disposal of high-level waste. It describes the seismological monitoring system developed by NO RAO in 2018 also briefly considering the seismotectonic conditions of the area. The paper describes the process that has been followed to select the corresponding sites and equipment layouts in the areas fitted with seismological monitoring stations with relevant instrumental characteristics being provided. It shows that considering the current stage of research, higher sensitivity was provided in the area as compared to the one associated with available regional seismological observations. It demonstrates the efficiency of the built-up monitoring system with its sensitivity assessment provided both based on the calculated model and under real conditions. The long-term safety assessment performed for such a facility relies upon many factors with the seismic hazard level within the area of the monitored facility also taken into consideration. To provide most reliable evaluation of seismic parameters, continuous seismological monitoring should be performed over a several years’ period along with the sensitivity assessment of the selected monitoring system. The seismological monitoring system should focus not only on the general study of the monitored territory, but also on the areas assumed as zones of most probable seismic event occurrence, i.e. areas involving tectonic faults. The relevance of this task has been repeatedly emphasized in the course of multiple discussions on this issue featuring the representatives from SC Rosatom and the Scientific and Engineering Centre for Nuclear and Radiation Safety. The monitoring system fitted within the repository area meets relevant regulatory requirements. In accordance with the existing requirements, to reduce the uncertainties in the seismic hazard assessment of the territory, the implementation of certain measures was recommended during further development of the local seismological monitoring network to identify and assess the potential of hazardous geodynamic zones.

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