Paleoseismicity along Adyr faults (on example of Kokonadyr-Tegerek fault in South-Western Issyk-Kul lake region, Tien Shan)

Abstract

We have studied paleoseismicity along a zone of the Kokonadyr-Tegerek adyr (foothill) fault in SW Issyk-Kul Lake region. It was shown that, although seismic movements continue along a zone of the tectonic contact of Paleozoic rocks of the Kokonadyr-Tegerek uplift and Quaternary deposits of the Alabash-Konurolyong depression, main number of appearance of seismogenic ruptures in the surface shift southward on hundreds of meters from the adyr fault mentioned above. This process leads to a formation of multiple fault scarps and compensation grabens in their back parts. According to data of radiocarbon dating along the Kokonadyr-Tegerek fault zone there were 4 strong Holocene earthquakes occurred during time intervals: 1771–1785 AD, 1440–1515 AD, and also possibly in 2310–745 BC and 640–5300 BC. Judging by parameters of the fault scarps their magnitudes were M ≥ 7, and seismic intensity I0≥ IX. Strong seismic activity along the Kokonadyr-Tegerek fault zone continues at least from Mid-Pleistocene. Evidences of this statement are uplifted and abandoned river valley of that time in the uplift with the same name as well as significant accumulation of the lacustrine sediments in northern part of the Alabash-Konurolyong depression. Large thickness of the sediments is tied with glaciers melting in the northern slope of the Terskey Ala-Too Range, and abandoned valleys testify on significant tectonic damming. Most proper model explaining formation of the adyrs (foothills) in the southern part of the Issyk-Kul Depression is a model of a gently dipping main fault flattening out northward, which is complicated by the underthrusts. All obtained data can be used at compilation of a new Map of Seismic Hazard of Kyrgyz Republic.