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

Alessandro Tibaldi,John Gierke,Nino Tsereteli,Thomas Oommen,Paolo Oppizzi,Zurab Gogoladze

doi:10.5194/nhess-19-71-2019

Abstract

Abstract. 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 km2. 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±12×106 m3. The opposite, eastern slope of the same mountain ridge is also affected by wide deformation affecting an area of 0.37 km2. 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.

Highlights

GPS data and plate tectonic models indicate that the Greater and Lesser Caucasus are tectonically very active, with ongoing mountain building processes comprising complex deformation with vertical and horizontal strain partitioning (Rebai et al, 1993; Koçyigit et al, 2001; Reilinger et al, 1997, 2006; Tan and Taymaz, 2006; Pasquaré et al, 2011)
North of the Enguri dam, below the carbonatic strata, there are Jurassic deposits made of sandstones, tuffs, tuff-breccia and gypsum layers that locally crop out along the southeastern side of the artificial water reservoir (Fig. 4)
For the first time, the evidence and characteristics of two large landslides located near the Enguri dam and water reservoir, in the southwestern part of the Caucasus (Republic of Georgia)

Summary

Introduction

GPS data and plate tectonic models indicate that the Greater and Lesser Caucasus are tectonically very active, with ongoing mountain building processes comprising complex deformation with vertical and horizontal strain partitioning (Rebai et al, 1993; Koçyigit et al, 2001; Reilinger et al, 1997, 2006; Tan and Taymaz, 2006; Pasquaré et al, 2011). These processes result from the convergence and continent–continent collision that is still developing between the Eurasian and African–Arabian plates (Avagyan et al, 2010; Adamia et al, 2017) (Fig. 1). Are subject to gravity effects that can be enhanced by earthquake shaking (Gutierrez-Santolalla et al, 2005); it has been widely demonstrated that this shaking can cause the generation of shallow landslides and deep-seated gravity slope deformations (DSGSDs) in active seismic areas

Results

Discussion

Conclusion