Gravitational Seismodislocations in Mountainous regions of Southeastern Kazakhstan

Abstract

Data on rock falls and landslides caused by strong earthquakes in the Zhetysu Alatau, Ile Alatau, Kungei Alatau and Teriskei Alatau mountain ranges on the territory of Southeastern Kazakhstan are presented. The study revealed more than 60 large seismogenic rock falls and landslides, the volume of 25 of them varies from 10 to 100 mil. m3, and the volume of the four largest exceeds 100 mil. m3. The volume of the largest rock fall in the valley of the Ulken Almaty river in the Ile Alatau mountain range is estimated at 380 mil. m3. The highest density of seismogenic landslides was recorded in the low-mountain zone of the northern slope of the Ile Alatau range where the magnitude 9 earthquake of 1887 caused a massive formation of landslides with the volume totaling more than 400 mil. m3 and a density of 1/5 km2. The proportion of landslide-affected areas is estimated at 5% of the area of their occurrence. In the mid- and high-mountain zones of Zhetysu, Ile and Kungei Alatau, the density of seismogenic rock falls varies from 1/100 to 1/50 km2, and the proportion of rock fall-affected areas varies from 1 to 1.5%. It is found that seismogenic rock falls have dammed 26 lakes, and the volume of nine such lakes exceeds 10 mil. m3. The largest rock fall-affected lakes is Upper Zhasylkol in the valley of the Aganakty river in Zhetysu Alatau with the volume of 44 mil. m3. Data from earthquake catalog were used to compile the map for the recurrence frequency of earthquakes of magnitude higher than 6, capable of causing seismogenic rock falls and landslides. It is found that during the last 130 years, in Ile and Kungei Alatau such earthquakes recurred four times. It is established that earthquakes with maximum magnitude 9 are possible in the mountainous regions of Southeastern Kazakhstan.