Determination of initial seismicity score and seismic microzoning of infrastructure area of Kolyma Hydro Power Plant

Earthquakes’ nature was studied and detailed seismic zoning (DSZ) and seismic micro-zoning (SMZ) were carried out for the Kolyma hydro power plant (KHPP) region, considering new geological, geophysical and seismological data. DSZ was based on tectonic zoning maps of Magadan region and seismological monitoring data in the vicinity KHPP facilities, carried out by Magadan Branch of Geophysical Survey of Russian Academy of Sciences. Eight source zones and 10 faults generating earthquakes were identified. Hypocenters of potential maximum earthquakes were determined. They are associated with the largest deep faults: Debinsky, Chay-Yuryinsky and Ulakhan and can cause ground shake in the area of main structures with intensities I= 8.8, 8.5 and 8.4 scores, which is consistent with OSR-2015-C map, selected as the main one for objects with increased level of responsibility. According to the DSR results, the initial seismicity of KHPP area on OSR-2015-С map was 8.8 scores. With repeatability of ~ 5000 years, the magnitude of the most dangerous earthquake for KHPP facilities will be M=6.5, with epicentral distance of 10 km. The obtained results of the DSZ were the initial estimates of seismic impacts for SMZ. The basis of SMZ is the nature of soils of the upper part of the section of the structures zone. The rock outcropping area was chosen as a reference, where the initial seismicity, taking into account DSZ, was 7.8 scores. The calculated increment of the score and the calculated intensity of the seismic impact on the areas of the main structures of KHPP were calculated. Moreover, in areas characterized by different engineering and geological conditions of the soils of the upper part of the section, both the method of direct registration of earthquakes and explosions, and the method of acoustic stiffness were used. According to both methods, the maximum shaking of the area of the main KHPP facilities amounted to 8 points, which is 1 point lower than the OSR-2015-C map