Landslides near Enguri dam (Caucasus, Georgia) and possible seismotectonic effects

摘要

The Enguri dam and water reservoir, nested in the southwestern Caucasus (Republic of Georgia), are surrounded by steep mountain slopes. At a distance of 2.5 km from the dam, a mountain ridge along the reservoir is affected by active deformations with a double vergence. The western slope, directly facing the reservoir, has deformations that affect a subaerial area of 1.2 km(2). The head scarp affects the Jvari-Khaishi-Mestia main road with offsets of man-made features that indicate slip rates of 2-9 cm yr(-1). Static, pseudostatic and Newmark analyses, based on field and seismological data, suggest different unstable rock volumes based on the environmental conditions. An important effect of variation of the water table is shown, as well as the possible destabilization of the slope following seismic shaking, compatible with the expected local peak ground acceleration. This worst-case scenario corresponds to an unstable volume on the order of up to 48 +/- 12 x 10(6 )m(3). The opposite, eastern slope of the same mountain ridge is also affected by wide deformation affecting an area of 0.37 km(2). Here, field data indicate 2-5 cm yr(-1) of slip rates. All this evidence is interpreted as resulting from two similar landslides, whose possible causes are discussed, comprising seismic triggering, mountain rapid uplift, river erosion and lake variations.