PALEOSEISMICITY OF THE SOUTHERN ISSYK-KUL LAKE REGION AND GEOECOLOGICAL PROBLEMS OF THE KADZHI-SAI URANIUM TAILING FACILITY (KYRGYZ REPUBLIC)

Korzhenkova L.A.¹,  Korzhenkov A.M.², Makeev V.M.¹ 

¹Sergeev Institute of Environmental Geoscience RAS (IEG RAS) Ulansky per. 13, bld. 2, Moscow, 101000
² Sсhmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia

The research is aimed at studying rare and strong paleoseismicity in the southern Issyk-Kul Lake region using the methods of paleo- and archeoseismology. In the Middle Ages, this region was under the recurrent impact of earthquakes, which could have led to catastrophic consequences, i.e., the destruction of medieval civilizations. These disastrous processes are not excluded now. The research region includes the southern coastal zones of Lake Issyk-Kul with their industrial, residential, economic and other infrastructure. For its safe functioning, knowledge about the mode of earthquakes in the past and in the present is necessary. Paleoseismological studies in the southern Issyk-Kul Lake region permitted us for the first time to identify the centers of strong ancient earthquakes in relief, i.e., the seismic scarps in the immediate vicinity of the Kadzhi-Sai tailing dump. In the isoseismic earthquake areas, significant rock failures were registered: landslides, disruptions and landslides. Based on the radiocarbon dating of samples, the age of these seismic events were determined. Their recurrence as once every several hundred years was calculated, with the magnitude Ms ≥ 7 and the seismic intensity Io ≥ IX. Structurally, the earthquakes, with their sources being localized in the upper part of the earth’s crust, are associated with neotectonic and modern deformation zones. These are deep thrusts of a southern dip and piedmont uplifts-adyrs of a reverse-dip type and a northern dip. The latter are localized in the frontal part of large uplifts moving towards the troughs. The formation of these zones with an opposite type of development is associated with the subhorizontal contraction of the Tien Shan Earth’s crust and its orogeny. Matter and structural movements lead to the redistribution of the Earth’s crust thickness and the formation of high mountains. Due to counter deformations, stress and strain concentrate in faults to form potential seismic centers, including catastrophic. The territory of the Kadzhi-Sai uranium-tailing dump is under the threat of destruction due to seismic hazard and secondary intense exogenous processes, i.e., landslides and mudflows. Earthquakes, as a rule, cause landslides in semi-hard Neogene rock of the Issyk-Kul suite, on which loose radioactive waste is stored. It has been found that atmospheric precipitation eroding the tailing dump flows not only into the mudflow trap, but also passes it towards Lake Issyk-Kul. The water that has been accumulated behind natural dams on the slopes of ridges may once break through the obstacles holding them and turn into a powerful debris flow. The constructed mudflow traps are not currently adequate to the existing threat in terms of their volume and location. To arrange engineering protection of radioactive waste sites from hazardous processes, it is proposed to conduct additional studies for assessing seismic, landslide and mudflow hazards.

Key words: paleoseismology, archeoseismology, faults, seismic scarps, landslides and taluses, rockslides, uranium tailings, tortkuls, adyrs, caravanserais

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