Visibility Graph Analysis of Seismicity around Enguri High Arch Dam, Caucasus

The visibility graph method is applied to the interevent times, interevent distances, and magnitude sequences of the seismicity that occurred around the Enguri dam, Georgia, from 1974 to 1989 and from 2009 to 2016, to calculate the so-called mean connectivity degree. The time variation of the mean connectivity degree of the three seismic series shows the presence of periods in which it is beyond the 95% confidence band, consistent with significant time-clustering behavior (measured by the coefficient of variation of the interevent times). In particular, the anomalous behavior of the mean connectivity degree between 1979 and 1981 is probably linked with the initial filling of the dam that started in 1978 and ended in 1984; whereas most of the anomalous mean connectivity degree identified after 1984 can be considered as co- and preseismic signatures of a few large earthquakes that struck the area.